MCS - Microbes and Disease

- Pathogen? - An organism that causes disease - Pathogenicity? - The ability to cause disease - Virulence? - A relative measure of the disease causing potential of a pathogenic organic - Virulence factor ? - A pathogen derived substance or structure contributing to virulence or damage causing ability - Antibiotic? - A substance produced by microorganisms, which at low concentrations can kill or inhibit the growth of other microorganisms - The respiratory route - through lungs - The faecal oral route- ingestion of faecal - What are the 3 transmission strategies derived organisms in humans ? - The venereal route- Acquisition through sexual practices - Adherence mechanisms through use of microbial adhesions - Active interference with removal mechanisms such as the muco-cilliary escala- Give examples of evolutionary adaptator- often achieved by producing chemitions in the body ? cals such as toxins - Resistance to immune attack and destruction- coverings and cell wall adaptations achieve this in many cases - What comes first, non specific responses of the innate immune system or activated adaptive immunity? - Innate immune system - Features of viruses? - The genome = genetic information as double or single strand - The capsid= Protective protein cost made up of protein sub units called capsomers - Gives the virus it's shape which can be icosahederal (sphere), helical/ rod shaped and complex (mix of both) 1 / 10 - The envelope= Not present in all viruses and derived from host cell membranes - The envelope also has viral proteins or spikes 1) Attachment= to a cell permitting replication 2) Penetration= Can be via cell membrane or by endocytosis 3) Un coating= release or genome from capsid 4) Subversion= Where the viral genes - Describe the states of virus replication take over the host cell machinery to make new virus 5) Expression= Viral genes are expressed 6) Assembly= Often at sites of release under the cell surface on the cytoplasmic side 7) Release= of virus particles - What are the 2 types of antibiotic resistance ? - Natural/innate resistance - Acquired resistance - Why don't viruses affect cells in the same way bacteria does ? - Viruses can't produce proteins independently and therefore can't produce proteins toxic to cells that can be secreted directly in the same way bacteria can - Describe the spread of pathogens through the circulatory system - The circulatory system has an extensive network of arteries and veins which carry blood to all parts of the body so a pathogen entering the circulatory system could spread to any part of the human body - As the circulatory system and lymphatic system are interconnected, any pathogen can gain entry to the lymphatic system through the circulatory system 2 / 10 - Malaria - Describe a disease that can spread via - Caused by different species of the parthe circulatory system asitic protozoan Plasmodium - The female Anpoheles mosquito bites an individual with malaria - The male and female gametocytes in human blood enter the gut of the vector where they fuse to form the zygote - The zygote is deposited on the gut wall of the mosquito - Describe the life cycle of Plasmodium - The zygote -> oocyst-> thousands of falciparum in mosquitos sporozytes are formed in oocyst which eventually ruptures to release them - Some of the sporozytes migrate to salivary glands of the mosquitos - When the mosquito bites a healthy person, the sporozytes are transmitted into the bloodstream - The sporozytes from the blood reach the hepatocytes of the liver and each sporozyte then produces daughter cells called merozoites - Describe the life cycle of Plasmodium - The infected hepatocytes rupture to refalciparum in a man lease merozoites which enter RBC's and destroy them - Some of these merozoites develop into gametocytes which can be sucked up when bitten by a mosquito - The plague - Caused by yesrini pestis - The bacteria secretes a virulence factor - Another disease which can spread via called F1 protein which forms a protective gel like capsule around the bacterithe circulatory system? um and helps it escape phagocytosis - It reaches the lymph nodes and multiplies rapidly to produce the buboe - What is bacteraemia ? - The transient appearance of bacteria in blood 3 / 10 - What is septicaemia? - The chronic high level f bacterial growth in blood - What does Neisseria meningitidis cause? - Sudden abrupt and fatal form of fulminating septicaemia - What are the causes of antibiotic resistance? - Over-prescribing - non compliance - Indiscriminate use of antibiotics - Describe the different ways bacteria develop resistance - Gram-negative bacteria exclude antibiotics such as penicillin due to their impervious outer membrane (no fluid can pass through) - Some bacteria have efflux pumps which can excrete antibiotics - Some bacteria alter targets such as the structure of ribosomes or polymerases to alter binding affinity of antibiotics - Bacteria secrete enzymes such as b-lactamases which open the B-lactam ring and destroy the antibiotic - Other bacteria modify antibiotics by phosphorylation - Antiviral drug classification? - Nucleoside analogues which are toxic to the host - Protease inhibitors= Prevent viral replication by binding and inhibiting viral proteases that process large viral proteins into their individual components and therefore prevent virus maturation - Polymerase inhibitors= Replication of viruses is blocked selectively by blocking nucleic acid from being produced - Anthrax - Caused by inhaling Bacillus anthracis - Another disease which can spread via spores in soil of pastures - The spores germinate in human tissue the circulatory system ? to form bacilli - The bacilli are protected from phago4 / 10 cytes by a secreted capsule allowing it to survive and multiply - Leptospirosis - Caused by the spirochete leptospira interrogans - Another disease that can spread via the - Infects mammals such as rats and dogs circulatory system ? - Transmission to humans is through contaminated food and drink and entry through skin (as the bacteria is motile) - Cold sores+Herpes simplex virus (HSVI) - Herpes simplex virus multiplies in the oral mucousal cells and causes lesions which eventually ulcerate - Describe a disease that can spread via - The virus particles enter the sensory the CNS nerves and are transported to the dorsal root ganglion where they lay latent -Different factors such as stress/ illness/sunlight cause reactivation - Disease 2 which can spread through the CNS ? - Genital herpes - Caused by Herpes Simplex virus (HSVII) - infects genital mucosa and causes lesions - Transmitted through genital secretions - Disease 3 which can spread through the CNS ? -Chicken pox and Shingles - Chicken Pox is caused by Varicella zoster virus in children - Shingles is caused by the varicella zoster virus in adults - Travels in sensory nerves - Rabies - Caused by bullet shaped virus called - Disease 4 which spread via the CNS ? Rhabdovirus - It rapidly multiplies in the grey matter of the CNS 5 / 10 - Protozoan Parasites - Caused by amoeba such as Naegleria fowleri - Disease 5 which spreads via the CNS - it's found in natural springs and enters ? the nose of swimmers - Spreads through the olfactory nerve to the olfactory centre in the brain - Direct interactions such as production and utilisation of offensive virulence fac- Damage in the human host is produced tors as a part of the host pathogen interac- - Indirect interactions= Interactions with tion. What 2 ways is this mediated ? the host immune response that causes damage. For e.g, inflammation of blockages in organs such as the kidneys - The exotoxins- secreted from the cell to cause effects - What are the 2 main categories of mi- The endotoxins- structural components crobial toxins ? of the cell wall that interact with the immune system to cause severe diseases - Give examples of endotoxins - Give examples of exotoxins - Lipopolysachharides - Lipotechoic acids- gram positive - Zymozan ( a component of yeast membranes) - Multi component toxins. They consist of an active or toxic portion and moiety that helps to translocation the toxic part into thr cytoplasm of a host cell. They can also be called A-B toxins where A is the toxic part - Multi component toxins are site specific and exert their action on specific structures of the body 6 / 10 - The neurotoxins produced by clostridium botulinum and clostridium tetani at the nerve synapse - Examples of site specific toxins ? - Explain the mode of action of the Cholera toxin -Botulinum toxin blocks release of excitatory neurotransmitters, resulting in flaccid paralysis and respiratory collapse - Tetanus toxin blocks inhibitory neurotransmitters, resulting in continuous contraction of muscles causing spastic paralysis - The toxin interacts with G-coupled proteins to induce adenylate cyclase enzymes to make huge amounts of cAMP - This leads to electrolyte imbalance which induces massive water loss - Super antigens or super antigenic exotoxins exert their effects through interaction with the immune response - FOR EXAMPLE TOXIC SHOCK SYNDROME - What are super antigenic exotoxins? - Staph Aureus causes it - It activates a set of T helper cells which produce cytokines that communicate instructions to other parts of the immune system - It happens in an unregulated way leading to a massive release of cytokines - Define morbidity rate - The number of new cases of a disease during a specified period - Define Endemic - A disease or agent that maintains a slow but regular level in a given population or area - What is sterilisation? - A process of complete destruction or elimination of all viable microorganisms in or on a substance being sterilised 7 / 10 - Define disinfection - A process of removing pathogens from the surface of inanimate objects - Name different methods of sterilisation - Filteration - Heat - Moist heat sterilisation - Dry heat - Thermal death of bacteria - Gaseous sterilisation - Irradiation - Chemicals - Disinfection - Filtration summary - Removes viable and non viable particles - Mechanisms for removing microbes: sieving,adsorbtion and entrapment - Describe dry filteration - Purifies gases for sterile air - Uses depth filters for e.g, HEPA (High Efficiency Particulate Air Filters) - The cells are adsorbed for entrapped in the fibrous matrix - 0.2-0.22 um - Clarifies liquids employs thin sieve like - Wet filteration nominal pore diameter ? membrane filters made of cellulose esters or paper - Moist heat sterilisation? - The standard conditions for moist heat sterilisation in an autoclave are 15 psi, 121.6 degrees for 15 minutes - The time depends on the volume of the solutions - Dry heat sterilisation? - Hot air ovens use heat at 160-180 degrees for 2 hours - Glassware, metallic surgical instruments and non aqueous thermos table liquids are used with this method 8 / 10 - Moist heat= boiling water/ pressurised steam, 60-135 degrees, thermal death time is in minutes, hydrolytic damage by steam, used for sterilisation of surgical - Differences between moist heat and dry instruments heat sterilisation? - Dry heat sterilisation= hot air ovens, 150-180 degrees, thermal death time is in hours, oxidative processes, used for glassware and metallic instruments - Antiseptics= The destruction or inhibition of microorganisms on living tissues - They prevent or limit infection and are milder than disinfectants - Define antiseptics ? - Bactericidal= Antibiotics that kill or lyse - What is the difference between bacteri- bacterial cells cidal and bacteriostatic? - Bacteriostatic= Antibiotics that limit growth - What are the most common targets of antibiotics? - Metabolic reactions taking place in a cell or cell wall or cell membrane - What is the difference between folate -Bacteria synthesise folic acid whereas metabolism between bacteria and mamhumans obtain Folin acid from diet malian cells ? - Why are Quinolones important? - They inhibit DNA gyrase or topoisomerase and prevent super coiling of bacterial DNA - Minimum inhibitory concentration= MIC is the minimum concentration of a mi- Describe an assay for evaluation of microbial agent that can inhibit the visible crobial activity growth of the microorganism under given test conditions - Minimum Bactericidal Concentration (MBC) or Minimum Lethal Concentration - Describe another assay for evaluation (MLC) of microbial activity - MBC and MLC is the lowest concentration of antimicrobial that completely sup9 / 10 presses growth or kills microorganisms completely 10 / 10