Lecture 09: The Innate Immune System

Lecture 09 : THE INNATE IMMUNE SYSTEM • Introduce and define the immune system. • • The body’s defense system against: – Pathogens – Cancers – Organ transplants Functions to: – Keep microorganisms out – Remove microorganisms that get in – Combat microorganisms that remain inside – Fight cancer (mutated/transformed cells) Well-balanced immune system should be able to distinguish between SELF and NON-SELF (à pathogen) • List the major components of the innate 1st line of defense. Skin (the physical barrier) ● Functions to stop organisms before they get in ● No adherence 🡪 no invasion Mucous membranes (form thin and permeable barriers) • Mucous membranes line the: • Gastrointestinal (GI) tract • Respiratory tract • Genitourinary tract Mechanical removal ● Goblet cells produce mucous ● Mucous/ other secretions flush away microorganisms ● Ciliated cells in the respiratory tract 🡪 ciliary escalator Mucociliary escalator • A major defence mechanisms which protect the lungs • Involves ciliated cells in the respiratory tract • Goblet cells produce mucus • Prevent pathogen binding to host cells Secretions (provide protection) Tears, saliva • Lysozyme (breaks down peptidoglycan) Crevicular fluid ● Fluid that flows into the gingival crevice between the teeth ● Similar composition to blood serum (liquid part) and contains immune cells and molecules Gastric juice ● pH 1-2 Urine/vaginal secretions ● Flushing action, pH, etc. Normal flora (competition for space and nutrients) ● Normal flora takes up the receptors in the body for example in the intestines. ● This means that pathogens have a hard time being able to attach / adhere and take up receptors. ● Only way receptors can lose normal flora is through use of antibiotics ● E.g. Vitamin K plays a key role in helping the blood clot, preventing excessive bleeding and binding of calcium to bones • List and define the cell types involved in the 2nd line of defense. Neutrophils • Target bacteria & make up 60 – 70% of total WBC in blood • First to arrive and initiate phagocytosis at the infected site • Fast moving, short life span ~ < 1 day (no mitochondria) • Neutrophils form “NETs” when they die • NETs are sticky DNA that traps bacteria • Have vacuoles containing granules with anti-microbial proteins and inflammatory mediators e.g. myeloperoxidase (turns pus greenish-yellow); superoxide radicals Eosinophils • Major role in defense against parasitic infection • Secretes cytolytic enzymes upon contact with pathogens • Cells circulate in blood until recruited to inflamed tissue Mast cells • Most abundant in submucosal tissues • Cell surface receptor for immunoglobulin E (IgE) • Important role in allergic reactions • Release histamine once IgE receptor is activated Basophils • Found in blood • Similar function to mast cells • Release histamine from granules Macrophages • 3 – 8% of total WBC • Professional phagocyte (very efficient) • Also eats damaged host cells (e.g. dead neutrophils & other cells) • In blood circulation à called monocyte • In tissue à called macrophage (many types) • Can break down the infectious pathogen and present the ‘pieces’ (antigen) on receptors located on their cell surface • Antigen presenting cell à more about this later Granuloma (macrophage instigated) • Seen in M. tuberculosis infections and many fungal infections Dendritic Cell • Professional antigen presenting cell; phagocytic • Important role in activation of adaptive immunity • Carries antigen from tissues to the lymph glands where the T and B lymphocytes reside • Presents antigen to T helper lymphocytes to initiate an adaptive immune response Granules • Leukocyte granules contain chemicals and enzymes to break down pathogens and stimulate other immune cells • Two types of granules: 1. Lytic granules • 2. Contain digestive enzymes (e.g. lysozyme) to breakdown endocytosed pathogens Secretory granules • Function to kill pathogens that are too big to eat • Contain chemical messenger substances that attract other immune cells to the site (chemokines) Some have inflammatory mediators (like histamine) Natural Killer (NK) Cells • Lymphocytes without immunological memory • First line of defense against intracellular pathogens • Virally infected cells • Intracellular bacteria/protozoa • Cancer cells • Release cytolytic granules = targeted cell destruction Which cells are destroyed? The inflammatory response • Infected cells: microbial antigen presented on MHC I • Virally infected cells which have lost surface expression of MHC I • Cancer cells that have lost MHC I Inflammation ● The localized tissue response to infection or injury The inflammatory response ● Cuts lead to an inflammatory response o o o o o Swelling Heat Altered function Redness Pain ● If the cut is infected, WBC counts increase (mediate the immune response) ● Swollen lymph nodes 🡪 lymph nodes are where the immune cells (T and B lymphocytes) multiple, preparing for an effective immune response. Pus 🡪 mixture of dead cells, neutrophils and body fluid Abscess 🡪 accumulation of pus (pustules and boils) Examples of pyogenic (pus producing) bacteria • Describe the mechanisms involved in diapedesis, chemotaxis and phagocytosis. ● Streptococcus pyogenes ● Staphylococcus aureus Phagocytosis ● When a cell engulfs a solid particle Phagocytosis by APC 1. Bacterium binds to receptor on phagocyte 2. Phagocytosis – bacterium is engulfed by cell membrane 3. Bacterium inside the cell vesicle (phagosome) 4. Fusion of lytic granule and phagosome (phagolysosomes) 5. Digestion of bacterium by enzymes 6. Transport of bacterial fragments to cell surface 7. Release of waste materials Diapedesis: • The migration of cells from inside blood vessels across endothelium through cell junctions Chemotaxis ● Cytokines The directed movement of cells in a concentration gradient Cytokines ● Small proteins made by host cells ● Function to change the behaviour or communicate with other cells Types of cytokines: 1. • Discuss complement activation. Chemokines: • Cytokines that are used for attracting other cells to site of infection • Interleukins: • Cytokines that alter the function of other cells Complement system ● A group of serum proteins in the circulation (made in liver) which function to enhance the immune functioning and defend against pathogens ● Reaction occurs on the surface of a cell ● Pathogens can sometimes get into the blood circulation o E.g. meningococcal sepsis caused by N.meningitidis Complement pathways • Three activation pathways: 1. Classical Pathway (antigen dependent) • 2. Activated by antibody – antigen (Ab-Ag) complexes Alternative Pathway • Activated by cell surface molecules on pathogens • Cell wall materials (i.e.: polysaccharides) Activated complement • Membrane attack complex Complement is activated by one of three pathways – Once activated, a cascade of molecules function to amplify many aspects of inflammation – All pathways converge at formation of the C5 convertase, followed by the complement proteins C5 à C9 – Form the membrane attack complex (MAC) – MAC inserts into the bacterial cell membrane causing lysis Membrane Attack Complex (MAC) ● C5 initiates the generation of the MAC o ● • Membrane attack complex is the result of the deposition of C5b, C6, C7,C8 and C9 in target cell membranes This pore structure disrupts osmotic integrity, resulting in cell death Identify the most important activated complement products and their biological activity including neutralization and opsonization. Functions of Complement ● Opsonization ● Inflammation ● Lysis • Differentiate between MHC I and MHC II. Major Histocompatibility Complex MHC Class I • Receptor on surface of all normal nucleated cells • Healthy cells: “self” protein is bound in the MHC I • Sick cells (virus infected or cancer): may have a foreign peptide (non-self) bound in the MHC I • Provides a way for cytotoxic T cells to scan & detect intracellular infection (more on this in section 10) • NK cells detect cells that are not showing self-peptides and kill them • In humans MHC = Human Leukocyte Antigen (HLA) • Usually just called MHC MHC II ● Found only on macrophages, dendritic cells and B lymphocytes (antigen-presenting cells or APCs) ● Bind and present peptides to T-helper cells on MHC II in order to initiate the adaptive immune response Toll like receptors Pattern recognition receptors (PRR) Triggering TLRs leads to Summary ● Chemokine release 🡪 calls in help from circulation ● Proinflammatory cytokine release 🡪 activates neighbouring cells ● Increased microbiocidal activity 🡪 destroys ingested pathogens Antimicrobial substances ● Interferons (IFN) o o ● Antimicrobial peptides (AMPs) o o o Lecture 10 : THE ACQUIRRED IMMUNE SYSTEM Outline the elements of the adaptive (or acquired) immune system ● Produced by virally infected cells Defense molecule against virus Production is triggered by activation of TLRs Broad spectrum Examples Dermcidin 🡪 produced by sweat glands ▪ Defensins 🡪 produced by neutrophils and macrophages ▪ Thrombocidin 🡪 produced by platelets Adaptive immunity 🡪 specific defense o o o Specialized immune cells that have a specific response Can recognize self and non-self (important for vaccines) Have memory regeneration ▪ ● ▪ The specificity is based on antigen recognition Antigen 🡪 a foreign molecule recognized by the adaptive immune cells o o Elicit / cause an immune response Most immunogenic antigens are proteins Describe the functions of the adaptive response ● Takes time to develop (5-7 days) ● Highly diverse and specific ● Generates memory ● Mediated by: B lymphocytes (humoral 🡪 in the blood) o o B lymphocytes ▪ Produce antibodies in response to specific antigens ▪ Make cytokines (chemical signals that change other cells behaviours) ▪ APC that activates immune cells to combat infection by cellular mechanisms T lymphocytes (cell mediated) ● First antibody to be formed in response 🡪 IgM and then in 2nd exposure is IgG which lasts longer ● Antigen dependent 🡪 why memory cells are needed ● Have a lag response ● Produced in the bone marrow ● Antigen dependent ● Activated in peripheral lymphoid organs (e.g. lymph glands) o ● B cell activation depends on the antigen ▪ Thymus dependent (TD) antigens 🡪 proteins ▪ Thymus independent (TI) antigens 🡪 other molecules Differentiate into plasma cells or memory B cells also in peripheral lymphoid organs o Differentiate through clonal expansion (all proliferating cells will have the same B ell receptor (BCR) and specificity for antigen Antigen 🡪 a foreign molecule that can be recognized by adaptive immune cells and cause an immune response Epitope 🡪 is a specific site on an antigen recognized by immune cells or antibodies Antibody 🡪 is a protein produced by B cells that recognizes a specific epitope on an antigen Cytokines 🡪 ● soluble proteins secreted by immune cells ● Chemical signals that can change behaviour of other cells ● Can cause B cell proliferation (clonal expansion) and class switching Class switching 🡪 Basic antibody structure and functions ● Changing Ig produced by B cell (e.g. Igm 🡪 IgG) with no loss of antigen specificity ● Fab region o o o ● Variable region Antigen binding sites Different combinations at the variable givers rise to a large repertoire of different antigen specificity Fc region o o Constant region Recognized by other immune cells that have a Fc receptor (binding site) ▪ ● The part recognized by macrophages. Functions of antibodies o o o o o Opsonization 🡪 proteins / antibodies coat microorganisms to make it easier for macrophages to eat Complement activation 🡪 antibodies and antigen form immune complex 🡪 classical pathway and forms split products to help immune system fight Agglutination 🡪 Fab region can bind different antibodies at once so they are all clumped together and lead to more effective phagocytosis Neutralization 🡪 e.g. vaccines that have similar toxoids can lead to negating / neutralizing the effect of poison Antibody- dependent cell-mediated cytotoxicity 🡪 antibodies help NK cells and cytotoxic cells List the 5 types of antibodies and their functions. ● Immunoglobulin G (IgG) o o o o ● Most abundant antibody in serum (80%) Transferred from mother to unborn child via placenta (child has immunity for about 6 months) Highly efficient to activate complement. Really likes Fc receptors on phagocytic cell membranes and readily start process of opsonization Immunoglobulin M (IgM) o o o o o o 5-10% of serum antibody 1st antibody produced in initial primary response. 1st antibody to be synthesized by neonates When in membrane bound form (monomeric) is forms the BCR (B cell receptor) Plasma cells secrete soluble IgM as a pentamer (5 molecules connected by a joining chain) IgM is more efficient to activate complement ● Immunoglobulin A (IgA ) o o 10-15% of antibody in serum Predominant antibody in external secretions ▪ o o o ● ● Extremely low concentrations in serum (0.0002% of serum antibodies) Responsible for allergies Binds Fc receptors on mast cells and eosinophils Plays an important role in neutralization of parasites Immunoglobulin D (IgD) o o o Define serum and plasma Exists as a monomer, but dimer can form and these are held by J-chain (used for easy transport across mucosal surfaces) Prevents attachment of bacteria or viruses to mucosal surfaces, thus prevents colonization IgA secretd in breast milk and protects the new born during the first few months of life Immunoglobulin E (IgE) o o o o ● 0.2% of serum antibodies Expressed at the cell surface of mature B cells along with IgM Biological function not well established but may be involved in mucosal immunity Serum o o o o Yellow liquid separated from coagulated blood after is is centrifuged and fibrin removal Rich in proteins Mostly used for lab testing Contains active blood clotting proteins. ▪ ● Used to check glucose levels or electrolytes Plasma o o o o Yellow fluid obtained by treating blood with an anticoagulant. RBC’s are removed by centrifugation Sometimes used for lab tests. Contains intact blood clotting proteins that have been activated. ▪ Explain how a defect in T cells can cause immunodeficiency Breast milk, saliva, tears and mucus in the bronchial, digestive and genitourinary systems Used for blood clotting disorders. T lymphocytes Cytotoxic T Lymphocytes (CTLs): CD8+ • target and directly kill virus-infected cells, tumour cells, or cells from a tissue graft Helper T Lymphocytes: CD4+ • produce cytokines that support inflammation and activates other immune cells • activate B cells which leads to antibody production • Activate T cytotoxin cells Regulatory T Lymphocytes: • can suppress other immune cells Development • Immature T cells travel to the thymus from the bone marrow • In the thymus, development is dependent on self MHC molecules and antigen • Cells are programmed so they don’t auto-react to self Activation • In peripheral lymphoid organs (e.g. glands) • MHC and antigen-dependent Differentiation • Become effector cells (Th or Tc) or memory cells Partial Immunodeficiency • Loss of function or numbers • Patients highly prone to infections Auto-Immunity • T cells unable to differentiate self from non-self • Hyper-immune responses Severe Immunodeficiency • Severe Combined Immunodeficiency (SCID) • Fatal if untreated by bone marrow transplant Acquired Immune Deficiency Syndrome • HIV hijack Th cells Differentiate between necrosis and apoptosis Apoptosis: programmed cell death • death of cells that occurs as a normal part of development or as a targeted event • does not trigger inflammation since “clean up” of apoptotic bodies is done by phagocytic cells Necrosis: caused by cell injury or infection/toxins Summary • death cell that is triggered by extrinsic factors • detrimental to host and accompanied by an inflammatory response • We need both the innate and adaptive immune systems to maintain health • The adaptive immune system is composed of humoral immunity (B cells and antibodies) and cell-mediated immunity (cytotoxic T cells/T helper cells) • The two arms of the immune system will interact with each other (cross-talk) and do not work completely independent of each other Lecture 11: HYPERSENSITIVITY AND VACCINES Describe the 4 types of hypersensitivity and give an example of each ❑ Four major types: o o Type 1: “Allergy”: Immediate IgE mediated (anaphylactic) o Localized (hives, hay fever, asthma o General anaphylaxis 🡪 Type 2: “Cytotoxic” (cell bound antigens) o o Transfusion reactions, Hemolytic Disease of the Newborn (HDN) Type 3: “Immune complex-mediated” (soluble antigens) o o SHOCK Serum sickness, Arthus reaction, SLE Type 4: “Delayed cell-mediated” (no antibodies involved) o Tuberculin test, contact hypersensitivity ❑ Immune reactions that can cause tissue damage ❑ All “Hypersensitivity” reactions require previous exposure to the antigen ( here called allergen) Type 1 Reactions ❑ Localized • Hives, “urticaria”, allergic rhinitis, hay fever ❑ Systemic • Result: shock • Need to carry Epi-pen e.g. peanut allergies ❑ sensitization, activation, and effector phases 1. Sensitization: result of classical antigen presentation with T helper cell involvement and B cell activation. 2. Activation: Cross linking of at least two IgE molecules bound to Fc receptors on mast cell - triggers mast cell/basophil degranulation 3. Effector: 2 phases ❑ Primary mediators released: histamine, eosinophil chemotactic factor, neutrophil chemotactic factor, proteases ❑ Secondary mediators released: leukotrienes and prostaglandins Type 1 systemic reactions ❑ Immediate reaction (minutes) ❑ life-threatening impaired breathing due to swelling of the airways. ❑ Uterine cramps, involuntary urination/defecation = due to smooth muscle contraction. ❑ Edema from fluid leaking into tissue spaces. ❑ Blood pressure drops dramatically, leading to life-threatening anaphylactic shock. Type 2 (Cytotoxic) HDN (hemolytic disease of the newborn) RhD- mother and RhD+ babies ● Involves complement, cell bound antigen and IgG or IgM antibodies ● Prevention of Rh sensitization o ● Rhogam (anti-Rh antibodies) given before and after delivery (to mom), rapidly eliminating fetal red blood cells from maternal circulation before B cell activation can occur Other transfusion reactions: o ABO incompatibilities ▪ . Type A blood – RBC have A antigen on them and individuals produce anti-B antibodies. If Type A blood type is transfused with B or AB blood then there will be an antigen- antibody reaction which with the aid of complement leads to lysis of the red cells Type 3 (Immune complex mediated) ● Immune complex (AB+AG) circulate in blood circulation (this is called soluble) ● Immune complex deposition is typically in skin, joints and kidney (glomerular basement membrane) ● Generalized type 🡪 systemic dissemination of AG-AB (IC) o E.g. poststreptococcal glomerulonephritis or SLE Bottom line 🡪 immune complex binds to endothelium, then activates complement which generates chemoattractant for neutrophils 🡪 these arrive, then release their granules and enzymes to damage tissue Type 4 (delayed cell mediated reaction) ● Slow response (2-3 days), had previous exposure and has T memory cells ● Activated macrophages are the principal effector cell in Type 4 ● Lytic enzymes that leak from activated macrophages cause local tissue destruction. CTL induced by Th1 cells may also participate in tissue destruction ● DTH responses can cause allergies responses such as contact dermatitis e.g. skin reaction tom poison oak and poison ivy where an oil from the plant complexes with skin proteins (haptens) that are then presented by ski dendritic cells to T1 cells o Treatment 🡪 corticosteroids for contact dermatitis, immunosuppressive drugs including cortisone for transplant rejection ● Describe the different vaccine formulations List a use for each vaccine formulation Other types of type 4 reactions (tuberculin test, transplant rejection) Types of vaccines: 1. Attenuated whole-agent 2. Inactivated whole-agent and Sub-unit 3. Toxoids 4. Conjugated 5. Nucleic Acid 1. a. DNA b. RNA Attenuated whole agent vaccines a. Living but changed (weakened) microbes b. Antigens intact but virulence diminished c. Closely mimics real life infection (get a CTL response) i. The vaccine strain replicates in host cells d. 95% effectiveness, often life-long immunity i. Stimulates both humoral and cell mediated immunity (memory cells are created) 1. e.g. Sabin (polio), MMRV (measles, mumps, rubella, varicella) Disadvantage 🡪 microbe can mutate back to their virulent form and may cause disease, cannot be used for people with compromised immunity or pregnant women Inactivated and subunit vaccines a. Use the whole microbes that have been killed, usually by formalin or phenol, or use parts of the organism (e.g. glycoproteins) i. e.g. rabies, Salk (polio), one of the Influenza vaccines, Gardasil, HepB b. No replication in host cell so it is safe for the immunocompromised, but due to no replication there are less antigens to stimulate an immune response and in the case of viruses there will be no presentation of proteins on MHC I and no CD8+ (cell mediated response) c. Strain will not revery to wild type d. Pregnant women can also be vaccinated with this e. Immunity does not last long so boosters will have to be given, some memory cells can be made but only B cell memory Toxoids a. Toxin isolated and chemically treated to preserve the antigenicity but to make the toxin non-functional b. Toxoid then used as vaccine to produce antibodies to toxin, not the microbe (only humoral immunity) c. Requires boosters for full immunity 🡪 e.g. diphtheria and tetanus e. 2. 3. 4. Conjugated vaccines ● Used for organisms that have polysaccharide capsules (poor antigens) ● The best antigens are proteins ● Children under 2 cannot respond well to polysaccharide antigens only protein ones ● Sometimes conjugated vaccines 🡪 polysaccharides from capsules are combined with a protein which is highly immunogenic o E.g. diphteria toxoid fools the immune system to react to the protein and at the same time get immunity to the carbohydrate ▪ Haemophilus influenzae type b ▪ Neisseria meningitidis ▪ Streptococcus pneumoniae Nucleic Acid Vaccines 5. 6. 7. DNA vaccines a. Introduce a gene for an organism into human host cells in hopes of staying there and getting transcribed b. Induce cells to produce organism specific proteins that stay and keep the immune system activate to the organism RNA vaccines a. Developed during the pandemic b. Based on mRNA from Covid-19 which has had a uridine base changed, so when injected does not get identified as an invading virus c. This change to mRNA is put into a lipid nanoparticle which will be taken up by our cells, then mRNA can go to the ribosomes and produce protein that stimulates our usual adaptive immune system. d. mRNA leaves the cells within 2-3 weeks Tuberculin Skin Test 🡪 diagnostic test using the Type 4 hypersensitivity reaction to gauge patient exposure a. Test to determine previous exposure to tuberculosis antigens (indicated by detection of memory cells) b. Small amount of PDD (purifies protein derivative) proteins from M.tuberculosis are injected into the skin of the forearm i. Positive test results in reddening and thickening of skin 48-72 hours after inoculation c. Cell-mediated reaction (Type IV) d. Disadvantages 🡪 i. cannot be used on unresponsive patients or those that are immunosuppressed as they do not react predictably, ii. this test does not test specifically for Tuberculosis 🡪 other mycobacteria species can also give a positive test. iii. People who have had the BCG vaccine will test positive and this can cause increased cost to determine if it is the vaccine effect or real exposure QuantiFERON – TB Gold Test ● New blood test for TB (tests for memory cells and activated T lymphocytes via production of interferon) ● Can be used to help confirm or rule out a latent or active tuberculosis infection or previous BCG vaccination ● Does not require the patient to return in 48 to 72 hours ● Requires a blood sample be collected from the patient and processes in the lab within 12 hours of collection, which complicated the clinical utility and the availability of the test in many situations Identify function of immunoglobulin in passive immunity ● Advantage 🡪 different antigens used than in the BCG vaccine ● Depending on the type of antibody can be passed onto the infant and give partial immunity • Discriminate between the four types of immunity Naturally acquired active immunity o individual exposed to antigens in course of daily life where clinical or sub-clinical infections can confer immunity e.g. unimmunized child gets chickenpox and develops immunity after the infection • Naturally acquired passive immunity o The natural transfer of antibodies o Maternal transfer of IgG antibodies over placenta o IgA antibodies in mother’s breast milk. e.g. baby is protected from Haemophilus influenzae until ~6 mo of life by mothers IgG antibodies • Artificially acquired active immunity – Result of vaccination, where specially prepared antigens (vaccines) are introduced into the body. – These substances are altered so that they can no longer cause disease, but can stimulate an immune response e.g. immunity after a mumps vaccine • – Artificially acquired passive immunity Involves the introduction of antibodies from an animal or person who is already immune to the disease e.g. varicella immunoglobulin given after exposure of unimmunized person to varicella (antibodies pooled from blood donor sera) Lecture 12: MECHANISMS OF PATHOGENECITY Define pathogenicity and virulence Distinguish between primary and opportunistic pathogens ● Pathogenicity: ● Virulence: the extent to which the microorganism is pathogenic ability to cause disease by evading or overcoming the host defenses Primary pathogens: always cause disease even in healthy immuno- competent individuals e.g. Bacillus anthracis Opportunistic pathogen: a microorganism that may cause disease if given the right circumstances e.g. Candida albicans – immunosuppression Mucor species – diabetics Pseudomonas aeruginosa – burns, CF, HIV, and neutropenic cancer patients Define virulence factor ● molecules/structures produced by pathogens that contribute to their “pathogenicity “or ability to cause disease e.g. Streptococcus pneumoniae is a pathogen, but only when it produces a capsule - a virulence factor Describe at least 3 virulence factors used by bacteria to evade the immune system 1. Capsules 2. Cell Wall Components 3. Biofilms 4. Enzymes 5. Invasins 6. Superantigens 7. Toxins 8. Secretion systems 9. Antigenic variation 10. Intra/extracellular growth Capsules ❖ Cell wall components Glycocalyx (= capsule, slime layer etc) -initially prevents the phagocyte from recognizing and ingesting the bacteria • many bacteria can produce capsules in the right environmental conditions M protein ● Streptococcus pyogenes o Heat and acid resistant protein in the cell wall that allows attachment o the bacteria to epithelial cells and inhibits phagocytosis Mycolic acids ● Mycobacterium tuberculosis o Biofilms Waxy substances in cell walls make the bacterium resistant to digestion inside the phagocyte . Exoenzymes: released from bacterial cells “united we stand” for bacteria o o Community of bacteria (single or mixed species), often surrounded by shared glycocalyx Reduces antibiotic effectiveness, WBC ● ● Leucocidin Collagenase: breaks down collagen (connective tissue) ● ● destroys WBC e.g. produced by S. aureus, Actinobacillus species) e.g. Clostridium perfringens penetration o e.g. Porphyromonas gingivalis in oral cavity, ● ● membranes o e.g. Clostridium perfringens o Proteases: inactivate antibodies and other body proteins, like IgA protease o e.g. Neisseria gonorrhoeae Kinase: ( e.g. Streptococcus pyogenes) Pseudomonas aeruginosa in lungs, on medical implants o break down fibrin and dissolve clots formed by the body to ● isolate the infection (important for spread) ● Hemolysin (Staph, Strep, Listeria, Lecithinase: destroy plasma Clostridium) o Secretion systems ● Some bacteria especially G- have genes ● Coagulase test Coagulase: Clots: converts fibrinogen to fibrin (protein strands), clot can wall the bacteria off from the host defenses encoded on their chromosome that code for pathogenic characteristics e.g. coding for a type 3 secretion apparatus ● Break down red blood cells, (Streptolysin S and O in S. pyogenes) Chromosomal region is where the genes are clustered (pathogenicity island) o E.g. Type 3 secretion apparatus enables a bacterial cell to inject proteins into a host cell killing or altering it **** Staphylococcus aureus (not epidermidis) Invasins • • • surface proteins on some bacteria which activate actin , the cytoskeleton of eukaryotic cells rearranges and facilitates bacterial engulfment into the host cell e.g. pedestal formation with Salmonella and pathogenic E. coli, Listeria rearrangement of actin to use as propellent Antigenic Variation ● Escaping the immune system o ● Intracellular growth Some pathogens can change their makeup The immune system will then see them as new pathogens o E.g. Neisseria gonorrhoeae and Trypanosoma species ● Some bacteria use their invasins to move from one host cell to another e.g. Shigella and Listeria ● Obligate intracellular growth: can only grow inside of host cells often in protected vacuole o E.g. Chlamydia, Rickettsia Pathogens have antigens on their surface to which B cells produce antibodies of their antigens as they replicate (mutate) ● ● ● Facultative intracellular bacteria: bacteria that can multiply outside of host cells, but often use intracellular growth as a means of evading the host defenses o Bordetella, Mycobacterium, Salmonella These bacteria infect intestinal epithelial cells laterally as well as from the outside in Describe at least 3 virulence factors used to enter host cells ● Mucous membranes ● Skin ● Parenteral route via the mouth ● Surgical sites and implants can provide a route to bypass these o Some microorganisms have preferred portal of entry and are only capable of causing disease via a specific route Tropism 🡪 the ability of a specific pathogen to infect a particular area ● Determinants of tropism o o o o o o o Define superantigens and provide an ❑ Distribution of cell receptors for microbes Accessibility of correct host cell types Other competing microbes Appropriate nutrients for growth Physical and innate defenses at the site of infection Age, etc plays into this! Permissive environmental condition – e.g. pH Also called Type 1 exotoxins example ❑ ❑ Protein antigens that stimulate a very large immune response o Normally <1% of Th cells are activated by an infection, but with a superantigen as activator, then the response can be measured in up to 20% of all Th lymphocytes o Unspecific binding to MHC II and TCR Results in excessive release of cytokines o This will result in nausea, fever, diarrhea, shock, death e.g. Staphylococcus aureus TSST-1 toxin which causes toxic shock syndrome Define toxins and provide at least 2 examples Some pathogens can remain at the site of infection and do not have to spread through the system to cause disease ● These pathogens may produce toxins that get into cells and cause the disease process o Examples of exotoxin producing bacteria ▪ Corynebacterium diphtheriae ▪ Vibrio cholerae ▪ Clostridium tetani, botulinum, perfringens ▪ Bordetella pertussis Toxins ● Often primary virulence factor ● Usually proteins that can produce fever, cause hear failure, diarrhea, edema or shock ● Can destroy cells 🡪 some inhibit protein synthesis leading to cell death 2 major types 1. 2. Endotoxin like LPS, Lipid A portion a. Molecule that contributes to the structure of the bacteria Exotoxins including superantigens a. An extra protein that is made by bacterium to affect cells other than itself Exotoxin Endotoxin ❑ ❑ outer cell wall Gram-neg bacteria - lipopolysaccharide (LPS) ❑ LPS is made of polysaccharide and a lipid A portion ❑ the lipid A is the endotoxin, heat stable ❑ causes chills, fever, weakness, aches, even shock and death produced by certain types of bacteria and released into the tissues (can be G+ or G- bacteria) ❑ genes for exotoxins are carried by bacteriophages or plasmids -e.g. diphtheria toxin, tetanus toxin 3 types of exotoxins ❑ activates the blood clotting system (DIC) (disseminated intravascular coagulation) ❑ 1. 2. 3. Cytotoxins – affect the cell Neurotoxins – affect brain and nervous system Enterotoxins – affect guts / intestines ❑ very potent proteins, but most are heat labile (sensitive) ❑ body produces antibodies called antitoxins for neutralization ❑ common structure is A-B toxins where A is toxic part and B Shock: life-threatening loss of blood pressure (if caused by bacteria called septic shock and if caused by Gram negatives called endotoxic shock) binds to cells Describe multiple ways bacteria use to share virulence factors between them Bacteria can share or acquire new DNA. Three methods of horizontal gene transmission: ❑ conjugation: transferral of plasmids containing genes for virulence attributes or antibiotic resistance ❑ transduction: acquisition of genes for toxin production e.g. C. diphtheriae bacteria via transferral by a bacteriophage ❑ transformation: acquiring gene for toxin, capsule production, etc by absorbing naked DNA from the environment around the bacterium Plasmids ● ● Small circular DNA molecules separated from the main bacterial chromosome Plasmids may encode antimicrobial resistance or virulence factors e.g. toxins, like tetanus toxin, staphylococcal enterotoxin and heat liable oximes of E.coli Bacteriophage ● Viruses which infect specific bacteria 🡪 transfer of genes by transduction ● E.g. Corynebacterium diphteriae Not pathogenic unless it is lysogenized by a phage and then produces toxin List some effects viruses can exert on host cells to cause disease Cytopathic effects (CPE) : ❑ Killing or damaging of the host cell ❑ Different strains of virus cause different CPE Syncytium formation ● Infected cells fuse to form a giant cell with many nuclei ● This giant cell dies when viruses use up all building material and cause necrosis of tissue ● Permits viral multiplication without exposing virus to antibodies o RSV, measles Lecture 13 : FLORA Describe the differences between normal and transient flora Normal flora 🡪 microbiota ● Animals and humans are free of microbes in utero, in healthy situation acquire bacteria at and after birth ● Newborns first contact with bacteria is usually lactobacilli from mother’s vagina ● With breast feeding and exposure to the environment, foods and other people these type of organisms are able to colonize their skin and intestinal tracts Normal flora in terms of region 1. 2. 3. 4. Respiratory – streptococcus species (mainly alpha hemolysis) GI – Bacteroides fragilis Vagina – Lactobacilli Skin – staphylococcus epidermidis Transient flora ● Microorganisms that may be present on body surfaces ● temporarily (days, weeks or months), then disappear ● Removed by handwashing (soap and mechanical scrubbing) ● Can be either pathogenic (disease causing) or nonpathogenic ● Do not necessarily cause disease unless special conditions prevail Anthrax caused by Bacillus anthracis ● principle pathogen of (Primary pathogen) ● Bacillus species ● large aerobic Gram positive bacillus with spores ● disease of herbivores ● found in soil and on vegetation ● spores very hardy - >50 yrs ● NO human to human Treatment 🡪 must be started early Penicillin is he drug of choice but ciprofloxacin used if resistance suspected 3 routes of infection for humans Susceptible to many antibiotics ● Pen, cipro, tetra, macrolides, clinda, chloro Inoculation (most common) - Usually acquired by contact with animals or animal hides Inhalation (e.g bioterror event in US 2002) - Not common in present time, historically wool sorters disease Ingestion - Common in carnivorous animals, also found in outbreaks in Africa usually due to ingestion of contaminated meat ● Plasmids responsible for acquisition of virulence factors: ● o ● polypeptide capsule (glutamic acid) - antiphagocytic ● Inert nonmetabolizing spores germinate to growing ● “vegetative”bacteria when conditions are right ● growth of bacteria leads to production of toxin ● 3 components of toxin: ● PA (protective antigen) LF (lethal factor) EF(edema factor) ● must have PA and either LF or EF for toxicity pX01 for toxins and pX02 for capsule Immunity and vaccines Smallpox (Poxviridae) ● Some animal species are naturally resistant to anthrax ● Vaccines are based on the capsule, poor antigenicity (no good vaccination for humans) ● Animal vaccines good for controlling disease in animals Ortho poxvirus, variola virus 🡪 small ● Enveloped DNA virus ● Other members of the orthopoxvirus family are: o Vaccinia, Monkeypox, Cowpox… ● Vaccinia and Variola virus differ in only one antigen and ● cross react. ● Immunity to smallpox = immunity to monkeypox ● Vaccinia used in smallpox vaccines (safe) ● Smallpox: two forms o o ● Variola major presents in different ways: o o o ● Define terms used to describe disease Variola major ~30% mortality Variola minor ~1% mortality Ordinary (discrete, semi-confluent, confluent) Modified/mild Flat and hemorrhagic Infectious, but not nearly as infectious as flu Zoonosis ● Disease transmitted to humans from an animal ● Animal may be healthy carrier or may be diseased ● Human 🡪 accidental host o Describe how diseases are transmitted Anthrax, Rabies, Tularemia, Chylamydia psittaci, west nile virus ● Incubation period 🡪 slight increase in organisms ● Prodrome phase 🡪 where we start to see slight symptoms (runny nose, sore throat, feel stuffy) ● Illness 🡪 most busy phase of bacterial replication (exponential) ● Death 🡪 if there is no immune response ● Period of decline 🡪 organisms decrease and immune system starts to get activated ● Convalescence 🡪 at the very end, recovering but still able to make other sick ❑ Horizontal transmission: o Transmission from one person to another through contact, ingestion, vectors, etc e.g. Chickenpox, Strep throat ❑ o Vertical transmission: transfer of a pathogen from a pregnant woman to her fetus e.g. Streptococcus group B or rubella virus Contact transmission 1. 2. 3. Direct contact 🡪 person to person (kissing, touching, sexual intercourse Indirect contact 🡪 agent transferred from reservoir to susceptible host by a non-living object (fomites, towels, cups and etc) Droplet transmission 🡪 microbes spread in droplet nuclei Vehicle transmission ● Transmission of infection by a medium 🡪 food, water, air, blood, IV fluids e.g. Hepatitis B by blood transfusion, M. tuberculosis by airborne route Vectors 🡪 arthropods (bugs) Define epidemiological terms ● Mechanical transmission 🡪 passive transport on the vector’s body e.g spread of shigella infection on house fly-feet ● Biological transmission 🡪 part of the life cycle of the microorganism is in the arthropods body e.g. Malaria and Anopheles mosquitoes Study 🡪 when and where disease occur Purpose 🡪 to control disease transmission Notifiable diseases 🡪 disease which physicians and laboratories are required to report to Public Health Incidence 🡪 number of diseases occurring within a specified time period Prevalence 🡪 number of diseases in a population at the particular point in time Morbidity 🡪 incidence of specific diseases Mortality 🡪 number of deaths from diseases Describe different types of infections including nosocomial infections ● Local infection: infection limited to one site ● Systemic infection: disseminated or generalized infection spread through body ● Focal infection: after spread of a systemic infection through the body, the organisms stay in specific areas (e.g. the liver for hepatitis) ● Primary infection: acute initial infection ● Secondary infection: appears as a complication of a primary infection Consequences of hospital infection ● Serious illness or death ● Prolonged hospital stay ● Expensive antimicrobials may be needed ● Patient may become a carrier or source and spread the infection in the community Spread of multi-resistant organisms List hazards you face as a health care professional ● Growing problem in health care institutions ● MRSA (methicillin resistant Staphylococcus aureus), VRE (vancomycin resistant enterococci), MRTB (multi-resistant M. tuberculosis), etc. ● Hand washing and adherence to hygienic routines is the only way to curb the epidemic ● Diseases: infectious, pose a risk for healthcare workers involved in ● the primary care of patients ● some of the more serious of these diseases are: o o o o HIV Hepatitis A,B,C Norovirus TB and other respiratory pathogens Plague SARS Sources of infection for healthcare workers ● infected patients ● soiled bedding, towels, dressings, other fomites ● contaminated needles ● surgical equipment (incl. N. meningitidis) Hemorrhagic fever viruses (e.g. Lassa fever, Ebola) Tularemia, How to avoid getting infected Acute vs Chronic Disease ● Hand washing: ● gloves, gowns, masks, goggles ● proper handling of used needles ● disinfection of the environment ● Acute disease: characterized by acute inflammatory responses where the neutrophil is the predominant cell type in the infiltrate ● o ● e.g. Boil caused by Staphylococcus aureus ● Chronic disease: characterized by chronic inflammatory responses where the predominant cell responders are mononuclear cells ● Slower type of infection ● Characterized by development of granulomas ● e.g. tuberculosis ● Sub-acute disease: intermediate between acute and chronic, usually a disease process that takes a long time to develop fully the number one preventative measure Pus production o o e.g. BSE or vCJD in humans ● Latent disease: causative organism may lie dormant for long ● periods of time before “reactivating” o e.g Herpes simplex or varicella Lecture 14 : SKIN AND EYE INFECTIONS Describe why the skin is a good barrier to infection ● Poor environment for microbial growth o o ● Microbial inhabitants often Gram positive ● Washing reduces numbers but does not eliminate normal flora o Identify the normal flora of the skin and give reasons why they survive on skin High moisture areas have larger microbial ● populations ● Both aerobic and some anaerobic bacteria grow on the skin o Staphylococcus epidermidis (dominant flora in skin) Mucous membranes o o o o o o Conjunctiva Quickly re-establishes from hair follicles, sweat glands etc ● ● Identify common eye infections, their causes and the results of disease (i.e. styes, blepharitis, conjunctivitis, keratitis, trachoma, inclusion conjunctivitis, ophthalmia neonatorum etc) Dry, high salt, sebum Lysozyme, antimicrobial peptides Line the body cavities Internal skin Sheets of epithelial cells attached to a basement membrane Goblet cells in skin secrete mucus to protect mucosal surface Cilia on some cells Acidic pH, normal flora must like to live at lower pHs ▪ E.g. respiratory tract: alpha streptococci ▪ Vaginal canal 🡪 lactobacillus ● outer surface of eye is exposed to the external environment and infectious organisms ● eyelid serves as a mechanical barrier to organisms ● tears with lysozyme and IgA: chemical barrier ● conjunctiva: especially susceptible to infection ● -vulnerable epithelial surface ● -covered by eyelid, creates warm, moist conditions ● Viral conjunctivitis Thin layer of mucous membrane lining the eyelids and covering the surface of the eye Bacterial conjunctivitis Keratitis Inflammation of the cornea 1. 2. Staphylococcus aureus eye infections Bacterial keratitis a. Characterized by pus Viral keratitis a. Less pus Blepharitis 🡪 inflammation of lid margins (infection) Stye 🡪 involvement of eyelid glands and follicles C.trachomatis Ocular Genital ● Types A-C ● ● Staphlycoccus sp. Types D-K, LGV Define terms used to describe rash lesions (i.e. macular, vesicular…) Identify characteristics of Staphylococcus aureus and Streptococcus pyogenes that make them major skin pathogens o o ● Gram positive cocci in clusters Non-motile, non spore forming, can and cannot have capsules 3 main species to know o o o S. aureus (primary pathogen) S. epidermidis (opportunistic) S. saphrophyticus (primary pathogen in the urinary tract, young women) S.aureus ● produce coagulase (differentiating characteristic from other staph species) ● - converts fibrinogen (sol) to fibrin (insol): 🡪 “coagulase positive staphylococci” ● -often yellowish colonies on BAP ● “yellow or golden staphylococci” ● MSSA (methicillin susceptible S. aureus) ● MRSA (methicillin resistant S. aureus) S.aureus virulence factors ● Coagulase ● Adhesion molecules ● Exotoxins and superantigens ● DNase ● Membrane damaging toxins (e.g. leucocidin) ● Capsule (sometimes) ● Protein A (Fc receptor) Impetigo ● Often in newborns and young children caused by staphylococci and streptococci ● Infection of epidermal layer ● Treatment 🡪 remove crusts, wash lesions and apply topical antibiotics ● Oral antibiotics if the infection spreads Toxic Shock Syndrome life threatening, multi-system effects -fever, vomiting, sunburn-like rash -effect of a “superantigen” -often the exotoxin causing this is TSST-1 (toxic shock syndrome toxin-1) in S. aureus -first identified in association with tampon use, now most common in patients following surgery, and intravenous drug abusers -most often caused by S. aureus, but can also be caused by GAS (group A streptococcus = S. pyogenes Treatment: IV antibiotic (usually semisynthetic penicillin like oxacillin) Scalded skin syndrome neonatal or 2° to toxic shock syndrome - due to S. aureus exfoliative toxin -often begins as skin lesion -exfoliative toxin affects the junctions of epidermal cells and causes loosening of cells Treatment: IV antibiotic Streptococcus sp facultative Gram positive cocci in chains -divided into three groups on the basis of their hemolytic reactions on blood agar: Beta hemolysis Streptococcus pyogenes ● Group A 🡪 S. pyogenes ● Group B 🡪 S. agalaciate ● Beta-hemolytic Important pathogen in skin infections, M protein 🡪 important “Group A”or “GAS” -pharyngitis, tonsillitis -impetigo -cellulitis, erysipelas -”childbed fever” -necrotizing fasciitis Post-infectious disease: acute glomerulonephritis rheumatic fever Streptococcal toxins and enzymes ● -streptokinase (dissolves blood clots - fibrin) ● -hyaluronidase (breaks down connective tissue) ● -deoxyribonucleases (degrade DNA) ● -proteases (e.g. IgA protease) ● -erythrogenic toxin (rash of Scarlet Fever) (superantigen) ● -Spe toxins (superantigens sometimes present in NF strains, are exotoxins that cause massive tissue damage and inflammation, like Flesh Eating Disease) ● Describe common skin diseases and their causes ETC. Erysipelas ● Infection of the dermal layer of skin ● Can progress to septicemia and fatal outcome ● Can begin as pharyngitis ● Treatment 🡪 antibiotics Streptococcal impetigo ● Treatment 🡪 removal of crusts, gentle washing and topical antibiotics Necrotizing fasciitis (flesh eating disease) 🡪 S.pyogenes or GAS ● Massive tissue damage found, cultures and Gram smears done, finding of ● Gram positive cocci in chains and growth of beta- hemolytic streptococci on blood agar plates. ● SpeA toxin detected in bacterial isolate. (superAg) Diagnostic symptom is disproportionate pain to injury!!!! Herpesviruses (DNA viruses) ● Extremely rapid progressive infection ● Streptococci invade deep and destroy the fascia (muscle ● sheath) liquifying the tissues as it progresses ● Mortality >40% even with timely treatment ● Very important with quick diagnosis, debridement of necrotic tissue and antibiotics ● HSV-1 o Causes cold sores ● very common, > 90% infected, ● most in childhood ● transmitted by oral route or direct contact ● causes “cold sores” ● remains latent in nerve endings (trigeminal nerve ganglia) and flares up with stress Herpes glaitortium 🡪 wrestlers on body Herpes whitlow 🡪 occupational hazard of healthcare workers Describe the diseases caused by measles virus and 5th disease (B-19) Measles (Rubeola ) ● Maculopapular viral disease caused by rubeola virus, an enveloped paramyxovirus (RNA) ● Extremely infectious (airborne) ● 90% attack rate in susceptible households ● Systemic disease with rash ● Other closely related viruses are canine distemper and rinderpest ● One serotype, humans only natural host ● No latent or persistent infection ● Often complicated by secondary bacterial infections like Staphylococcus aureus pneumonia and ear infections ● Blindness in children with vitamin A deficiency ● Rare fatal complication 🡪 subacute sclerosing panencephalitis (SSPE several years later) Classic measles ● Rarely subclinical ● Symptoms are respiratory: fever, malaise, anorexia, conjunctivitis, photophobia, myalgia ● Koplik’s spots (appear on buccal mucosa: red white and ● blue spots diagnostic of measles prior to rash) ● Maculopapular rash, starts behind ears, and spreads to face, upper arms and trunk, then legs ● Intense inflammation of lymphoid tissue and mucosa of the ● respiratory tract ● Tracheobronchitis and pneumonia common Measles causes immunosuppression ● Dendritic cells and monocytes are infected, antigen presenting activity compromised ● Circulating T lymphocytes are decreased by 50% ● Abberrant cytokine responses o o ● IL-4 and IL-10 increased, skews TH1 (cell) to Th2 (AB) Reduced macrophage activity Lecture 15 : UPPER RESPIRATORY TRACT INFECTIONS ▪ ▪ Bacterial infection ▪ Strep throat & complications ▪ Diphtheria ▪ Otitis Media ▪ Whooping cough (borderline URT/LRT) Viral infection ▪ Common cold ▪ Infectious mononucleosis (kissing disease) Identify some common causes of pharyngitis including the common cold The common cold ● >100-200 different viruses can cause a cold, so immunity ● not usually protective factor, no vaccines ● ~30-50% of colds caused by rhinoviruses (hosts are primates) ● 15-20% caused by coronaviruses o Infection easily spreads to sinuses, lower respiratory tract and middle ear Rhinovirus ● >50% of common colds caused by rhinovirus ● Small virus, RNA genome, non-enveloped ● > 100 subtypes, classed into 3 classes based on the receptor they bind to o 90% bind to ICAM-1 ● Transmitted mostly by direct contact (e.g shaking hands very efficient transmission), some by droplet ● Does not grow at 37°C, optimal at 33°C; therefore grows only in upper respiratory tract ● 10-12 hours incubation period ● Self-limiting infection: no antivirals, no vaccine Identify the cause and discuss the disease “Infectious Mononucleosis” Major cause: ● EBV: Epstein Barr virus (HHV 4) DNA, Herpesviridae, enveloped, latent in B cells ● Infectious Mononucleosis (IM) (“kissing disease”) ● Most people have the infection when very young and have mild or sub-clinical infection ● More severe disease when older (teenagers, college students) ● Systemic effects on cardiovascular and lymphatic systems ● Virus shed intermittently from saliva through life Symptoms of IM: EBV related cancer Discuss S. pyogenes pathogenicity in the respiratory tract ● -fever, sore throat, swollen lymph glands in neck, general weakness, fatigue, enlarged spleen ● Production of heterophile antibodies (weird antibodies that agglutinate other mammals RBC) ● -no function known for these antibodies but they are used for lab tests (e.g. Monospot) ● Ampicillin rash a complication (not just a rash!) if you have mono and are given beta-lactams. This is like a superantigen effect! EBV related cancer ● Associated with Burkitt’’s lymphoma and other B cell lymphomas ● Most common type of childhood cancer in Africa ● Association with malaria endemic areas Streptococcal pharyngitis (Strep throat) ● Streptococcus pyogenes (Strep group A) - beta hemolytic streptococci ● on inspection, strep throat cannot be differentiated from ● any other type of infection - laboratory tests necessary!!! ● rapid tests are available but if the test is negative and the suspicion continues send a swab to the lab! ● Need to treat all cases of Streptococcus pyogenes pharyngitis with antibiotics to prevent sequalae (complications coming after an infection) Scarlet fever ● S. pyogenes can produce an erythrogenic toxin o Rheumatic Fever ▪ Pinkish-red sandpaper like skin rash ▪ High fever ▪ Strawberry tongue (loses upper membrane and becomes inflamed) ▪ Scarlet fever varies in severity, may progress to glomerulonephritis or rheumatic fever ● Non-infectious complication of a S.pyogenes infection occurring after an infection has disappeare ● Cross reactivity of bacterial antigens with tissue antigens. o Explain how C. diphtheriae causes disease The first time you get strep throat with one of these strains producing this superantigen can get scarlet fever Some evidence of T lymphocyte invasion in addition to neutrophil damage ● Most often mitral valve damage ● caused by Corynebacterium diphtheriae, an aerobic Gram positive bacillus (non- spore forming) ● bacteria do not invade tissues - they produce an exotoxin (inhibits protein synthesis in host cells - tropism for nerve cells) ● once leading cause of mortality in children (9,000 ● cases in children 1-5 yrs in the early 1920’s ● Toxoid vaccine introduced in 1924 toxin you ● Vaccination has drastically reduced the incidence of disease in ● North America and Europe – now it is a rare disease here o Symptoms: ▪ sore throat, fever, malaise ▪ neck swelling (“bull neck”) ▪ nerve paralysis ▪ white-gray membrane across back of throat (fibrin, dead tissue, bacterial cells, toxin and neutrophils) Pathogenic strains of C. diphtheriae produce exotoxins that diffuse through tissues, cause death of epithelial cells in the throat and affect nerves (e.g. in heart and face). Typical thick gray membrane (pseudomembrane): -covers back of throat – very hard to remove, grows out of the tissue and bleeds if you try to dislodge it - can prevent breathing, obstructs air passage ● C.diptheriae 🡪 apathogenic unless transduction occurs by a bacteriophage which transfers the exotoxin gene o ● All isolates of this bacteria have to be tested for the toxin first ▪ Effects of toxin: myocarditis, cardiac failure, polyneuritis, death (toxin has an affinity for nerve cells) ▪ bacteria do not invade tissues, just expel exotoxin which can diffuse into other areas Treatment: antibiotics and antitoxin o o effective, but older people in population may only have effective protection in 20% of cases due to lack of boosters -tetanus toxoid is usually combined with diphtheria toxoid and pertussis DTaP Identify the causes of otitis media Discuss pathogenic mechanisms of Bordetella pertussis causing whooping cough Bordetella pertussis ● Small aerobic Gram neg coccobacillus ● Produces many exotoxins ● Does not invade tissues, colonizes ciliated respiratory epithelium and kills cells with tracheal cytotoxin ● Transmission: droplet ● Three stages of disease: o o o ● Catarrhal: cold like Paroxysmal: gasping cough Convalescence: healing Infants most at risk for: o o o Broken ribs Pertussis pneumonia Oxygen deprivation to brain Pathogenicity ● FTA filamentous hemagglutinin (for adherence) ● Pertussis toxin 🡪 systemic effects ● Tracheal cytotoxin 🡪 damages ciliated cells ● Lethal toxin 🡪 tissue necrosis ● Adenylate cyclase 🡪 reduces phagocytic activity ● LPS Treatment ● Treatment usually not effective for disease but reduces infectivity o Erythromycin Vaccine ● New acellular vaccine (against toxins) ● Combined with tetanus and diphtheria DTaP o 5 doses, new recommendations for re-vaccinating in early teens Lecture 16 : LOWER RESPIRATORY TRACT INFECTIONS Describe M. tuberculosis pathogenicity, latent infection and active disease Tuberculosis (Mycobacterium tuberculosis) • Leading cause of death world wide from bacterial disease • Capable of intracellular survival & growth in macrophages (facultatively intracellular) • No toxin produced. Inflammation- major pathogenic mechanism • Transmission: airborne • Bacillus, non-motile, acid fast Strict aerobe • Mycolic acid forms an impermeable barrier to entry of molecules into the bacillus. • Survive long period on dry surfaces. • Not visible in Gram stain (mycolic acid prevents Gram stain from entering the cell wall) • Stained with Ziehl-Neelsen (acid fast) stain. • Production of cord factor (causes bacteria to clump together and inhibits phagocytosis): this chemical is also toxic to host cells. After TB exposure Three things could happen: 1. Latent infection where few TB organisms enter macrophages and remain latent there 2. Primary tubercle forms but the immune system – can stop replication 3. Spread of active infection – this happens in immunocompromised individuals Primary infection: often in lung ● Host walls off the infection in a tubercule (a granuloma) o Tubercule ▪ Macrophage B and T cell collection with central caseation, TB cannot replicate because of low Ph and low oxygen concentration ● Disseminated infection 🡪 occurs if tubercule does not even form for bursts allowing bacteria to spread o This is then disseminated infection called miliary tuberculosis Ghon complex ● A calcified granuloma that shows on an x-ray Second dtage infection ● Miliary infecton ● Directly spread from first infection or a reactivation of a latent infection ● Characterized by spread of tubercles (granulomas ) ● You can get TB anywhere In the body ● Symptoms o weight loss, fever, night sweats, chronic cough, coughing up blood, lethargia (consumption) Mantoux Test 🡪 quantitative tuberculin test Tuberculosis Vaccine ● BCG: Bacillus Calmette-Guerin ● Live culture of Mycobacterium bovis ● In North America only given to children at high risk ● Effectivity of the vaccine is not very good and it doesn’t last ● very long! Therefore…. ● Adults – almost no effect, children some effect Treatment and antibiotic resistance ▪ Multiple drug regimens used to prevent development of drug resistance ▪ Treatment 6 mo – 1 yr because of slow growth of the bacterium ▪ MDR-TB and XDR-TB is a growing problem ▪ MDR-TB resistant to isoniazid and rifampicin (first line drugs) ▪ XDR-TB resistant to first and second line drugs Isolation and Quarantine Describe pneumonia caused by S. pneumoniae and the major virulence factor for the organism Typical: classically caused by S. pneumoniae, responds to penicillin treatment Atypical: caused by other organisms, penicillin resistant, includes virus, bacteria and fungi - most common cause of infection-related death globally - causes of pneumonia in adults and children different: Adults: Mainly bacterial Children: Mainly viral Pneumococcal (Pneumonia (Typical) • Encapsulated facultatively anaerobic Gram positive diplococci – Streptococcus pneumoniae (nickname: pneumococcus) • Most common cause of pneumonia, involves alveoli and bronchi • Symptoms: fever, rust coloured sputum (blood), breathing problems and chest pain • Often spreads to the blood • (bacteremia - septicemia - sepsis) • Vaccines • Conjugate (13 types) polysaccharide (23 types) S. pneumoniae Pathogenicity Many virulence factors • Capsule: >90 antigenic types - main virulence factor • Cell wall: lipoteichoic acids and peptidoglycan • Choline binding proteins for host cell attachment. • Autolysins : self-destruction, release other chemicals. • Pneumolysins: damage pneumocytes in lungs. Production of hydrogen peroxide, neuraminidase and IgA protease Pneumonia Risk Factors Identify and discuss characteristics of some viral causes of LRTI: RSV, Parainfluenza, Influenza ● Asthma ● Cystic Fibrosis ● Chronic Obstructive Pulmonary Disease (COPD) ● Weakened immune system (HIV, cancer…) ● Young children and elderly Bronchiolitis in infants • Usually after an upper respiratory tract infection • Disease restricted to children usually < 2 years • Bronchioles of children very small (diameter) - if the cells lining them are inflamed and swollen the passage of air to and from alveoli is reduced • Necrosis of epithelial cells (spread to the lung →interstitial pneumonia) RSV **RSV (Respiratory Syncytial Virus) • Enveloped, RNA, spread mainly by direct contact and occasionally droplet • Infants and children < 5 yrs ; elderly in nursing homes • Epidemics and seasonal : late winter and early spring • Life-threatening pneumonia and bronchiolitis in infants • Symptoms : coughing and wheezing • Premature babies highest risk for serious disease Treatment –no effective antiviral , new mRNA vaccine Prophylaxis: Synagis monoclonal antibody, (passive immunization), given only to premature babies with other risk factors (very expensive! 15mg/kg,, $260 US $/kg monthly) Croup (children): • Parainfluenza virus (PIV) (enveloped RNA) is a common cause of “croup”in small children • Swelling of mucous membranes in the respiratory tract • Larynx and trachea have non-expandable rings of cartilage and since children have narrow tubes, obstruction can occur Typical seal-like barking cough Influenza A • Influenza A,B,C are enveloped orthomyxoviridae, segmented RNA viruses • Influenza A + B have 8 RNA segments, C has 7 Only Influenza A has subtypes ● Hemagglutinin 🡪 glycoprotein used for attachment to the host cell ● Neuraminidase 🡪 helps newly formed viruses in the host cell to escape o Need these 2 for a disease to happen ● M2 ion channel 🡪 allows for acidification of the vacuole that the virus will be enclosed in Symptoms ● Malaise ● Fever ● Headache ● Myalgia ● Cough ● Sore throat Incubation period and infectious dose Identify the major cause of epiglottis, a life-threatening infection Define antigenic shift and antigenic drift for Influenza A virus ● Small infectious dose ● Incubation 1-5 days ● Virus viable on hard surfaces 24-48 hours ● Droplet transmission ● Most often seen in young children,usually due to H. influenzae type b ● Typical sign → children lean forward to breathe and drool ● Bacteria spread from nasopharynx to epiglottis, cause severe inflammation, and the epiglottis will swell shut → closing airways ● Life threatening, call for help to intubate! Antigenic Drift: ▪ Point mutations in the viral genome encoding for H or N antigens ▪ These strains cause the yearly infections (some cross- immunity from year before) Antigenic Shift: ▪ Recombination of the viral RNA segments with those from another human or an animal Describe Covid-19 and mechanism of pathogenicity ▪ Significant changes in the H and N surface antigens ▪ Leads to pandemics, no immunity to “new” viruses Covid-19 • New enveloped RNA virus belonging to the coronavirus family emerges in China late 2019, probably from a bat reservoir • Able to establish infection in humans globally • Four subtypes: alpha, beta, (human pathogens) gamma and theta (animal) • ß : SARS-CoV, Mers-CoV &“Covid-19 (Sars- CoV2)” • Heterogeneous: symptoms may vary and include: – Fever, conjunctivitis, pharyngitis, coryza, headache, dizziness, generalized weakness, vomiting, diarrhea, dry cough, shortness of breath – Lack of taste and smell, fatigue Severe disease usually presents after 9 days of infection How does this corona virus affect humans? • Glycoprotein spikes: responsible for tropism and attachment to host cell • Spikes have two functional units: S1 (used to bind to receptors on host cells) and S2 (used to fuse host cell and virus envelope) • Main receptor for Covid-19: Angiotensin converting enzyme 2 (ACE2) • ACE2 is highly expressed in lung, heart, ileum, kidney and bladder, on epithelial cells and some endothelial cells. New vaccines developed, antivirals are being developed What does ACE2 do? Risk factors for severe disease (ARDS or acute respiratory disease syndrome) • Vaccine development is a major push around the world • Few antiviral substances found that can shorten the duration of disease (not prevent) • A common cortisone derivative dexamethazone has been found to improve survival • This is angiotensin-converting enzyme 2. Normally it breaks down proteins ( especially angiotensin II) which can increase inflammation and the death of cells in the alveoli (critical for oxygenation of blood). • These harmful effects of ANG II are reduced by ACE2 • When COVID-19 is bound to ACE2 then it cannot prevent the damaging effects of ANG II • Age: immunosenescence – Most cases were at first in elderly patients – Many died due to multi-organ failure • Immunocompromise • Co-morbid conditions – • E.g. pre-existing lung or heart conditions Critically ill patients found to have: – Fungal Diseases lymphopenia, especially in the peripheral blood T cells – Increased plasma concentration of inflammatory cytokines (IL-6, IL-10), chemokines like IL-8, TNF alpha – Elevated D-dimer and fibrinogen = increased clotting (hypercoagulable) • Histoplasmosis • Coccidioidomycosis • Aspergillosis • Pneumocystis jiroveci (especially in AIDS and other immune-suppressed individuals like transplant patients)