Lecture 14: Skin and Eye Infections

(Skin and Eye Infections) Lecture 14 Skin · poor environment for microbial growth ↳ dry, high salt, sebum, lysozyme, antimicrobial peptides · Microbial inhabitants often G+ (more osmotically stable b/c of peptidoglycan layer) · Washing reduces numbers but does not eliminate normal flora ↳ quickly re-establishes from hair follicles, sweat glands, etc. · High moisture areas have larger microbial populations (armpits, groin) · normal flora of the skin can be anaerobic or aerobic ↳ dominating flora is Staphylococcus epidermidis** ↳ other micrococci sp ↳ diphtheroids: -corynbacterium sp: acrobes, on surface -propionibacterium sp: anaerobes, live under surface in follicles and glands ↳ yeasts: Malessezia furfur Mucous Membranes · line body cavities · "internal Skin" · sheets of epithelial cells attached to a basement membrane · goblet cells in skin secrete mucous to protect mucosal surface · cilia on some cells (respiratory, GI tract) · acidic pH, normal flora must like to live at lower pHs eg. respiratory tract: alpha streptococci vaginal canal: lactobacillus Normal Flora of the Eye Surface Eye Infections · Micrococcus sp. (eg. S. epidermidis) in small numbers external environment and infections organisms Normal flora of conjunctival surface: · alpha-hemolytic Streptococci in small numbers · diphtheriods (Corynebacterium sp.) in small numbers The interior of the eye is a sterile field Viral Conjunctivitis · mild infection and inflammation of the conjunctival membrane (pink eye) · outer surface of eye is exposed to the · eyelid is 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 and moist conditions · conjuctiva is a thin layer of mucous membrane lining the eyelids and covering the surface of the eye Keratitis · inflammation of the cornea · bacterial Keratitis - characterized by pus · viral Keratitis - less pus Eyelids Infected with Staphylococcus aureus · blepharitis: inflammation of lid margins +/- infection · Stye: involvement of eyelid glands and follices · Acanthamoeba Keratitis · Trachoma: Chylamidia trachomatis A-C ↳ ocular = types A-C ↳ genital = types D-K, LGV -note: you can infect your eye with a genital chlamydia, but then it is called “inclusion conjunctivitis” NOT trachoma ↳ genital doesnt cause eye, eye doesn't cause genital Ophthalmia neonatorum: gonorrhea in the newborn eye Skin Lesions · vesicle, bulla, macule, pustule (papule) Staphylococcus sp. · G+ cocci in clusters ↳ non-motile, non-spore forming (may have capsules) · 3 important species to know: ↳ S. aureus (primary pathogens) ↳ S. epidermidis (opportunistic) → normal flora ↳ S. saphrophyticus (primary pathogen in urinary tract of young women) · produces coagulase (differentiating characteristic S. aureus Virulence Factors · coagulase · converts fibrinogen (sol) to fibrin (insol) · exotoxins and superantigens · often yellowish colonies on BAP "yellow or golden · membrane damaging toxins (eg. Ieucocidin) · MSSA (methicillin susceptible S. aureus) · protein A (Fc receptors) → prevent bacteria S. aureus from other staph species) ↳ "coagulase positive Staphylococci" · adhesion molecules · DNase staphylococci" · capsule (sometimes) · MRSA (methicillin resistant S. aureus) from being opsonized Impetigo · infectious in daycares and elementary schools · often in newborns and young children, caused by: ↳ Staphylococci and Streptococci · infection of epidermal layer of skin · treatment: removal of crusts, washing of lesions and applications of topical antibiotics ↳ oral antibiotics only if 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 tampon use, now common after surgery and intravenous drug users · mostly caused by S. aureus, but also GAS (group A streptococcus) = S. pyogenes · treatment: IV antibiotics (usually semisynthetic penicillin like oxacillin) Scalded Skin Syndrome · neonatal or secondary 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. Grouping Based on Cell Wall Carbohydrates · divided into three groups on the basis of their · Beta hemolysis · facultative G+ cocci in chains hemolytic reactions on blood agar: ↳ alpha hemolytic ↳ beta hemolytic ↳ gamma hemolytic · landsfield typing Group A: S. pyogenes Group B: S. agalactiae · Alpha, gamma, and variable hemolysis: Group C: several strains Group D: (enterococci also known as S. faecalis) Group G: several strains Streptococcal Toxins and Enzymes · streptokinase: dissolves blood clots - fibrin · hyaluronidase: breaks down connective tissue · deoxyribonucleases: degrades DNA · proteases: (eg. 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 etc. Erysipelas · infection of the dermal layer of skin · can progress to septicemia and fatal outcome · can begin as a pharyngitis · treatment: antibiotics Necrotizing fasciitis (flesh eating disease) · diagnostic symptom: disproportionate pain to injury, extreme pain ↳ extremely rapid progression · G+ streptococci in chains, SpeA toxin (superantigen), beta hemolytic ↳ caused by S. pyogenes or GAS · high fever and extreme pain develop rapidly · sepsis can develop, streptococci invade deep and destroy the fascia (muscle sheath) and liquify the tissues ↳ before this sore weeps and becomes inflamed and edamatous (swollen) · mortality 40+% even with timely treatment ↳ must be quick with diagnosis and debridement of necrotic tissue and antibiotics ↳ reconstructive surgery may be required Herpesviruses (DNA viruses) warts = human papillomavirus (HPV) · 8 viruses in group that are human pathogens HSV-1 Cold sores HHV-3 (V2V) Chickenpox and shingles HSV-2 HHV-4 (EBV) HHV-5 (CMV) HHV-6 HHV-7 HHV-8 Genitalia herpes lesions Infectious mononucleosis Congenital disease + disease in immunocompromised Roseola Sometimes roseola, otherwise ? Kaposi’s sarcoma-associated HSV-1 · causes cold sores · Herpes gladitorium: wrestlers body-body contact · very common >90% infected, mostly in childhood · transmitted by oral route or direct contact · remains latent in nerve endings (trigeminal nerve ganglia) and flares up with stress Measles (Rubeola) · Herpes Whitlow: occupational hazard of healthcare workers · maculopapular viral disease caused by rubeola virus, an enveloped paramyxovirus (RNA) · Extremely infectious, airborne transmission ↳ 90% attack rate in susceptible households · systemic disease with rash · one serotype, humans only natural host · no latent or persistent infections · similar viruses: canine distemper and rinderpest Measles Cont'd · often complicated by secondary bacterial infections like S. aureus pneumonia and ear infections · blindness in children with Vitamin A deficiency (malnutrition) · rare fetal complications: subacute Sclerosing panencephalitus (SSPE several years later) - non curable, eventual death Measles Disease 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, 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 50% · Aberrant cytokine responses: ↳ IL-4 and IL-10 increased, skews Th1 cell to Th2 (AB) ↳ reduced macrophage activation Vaccine · live attenuated vaccine 95% effective after one dose. For non-responders, a second booster is needed · herd immunity: need 95% vaccination coverage in population · combined measles, mumps, rubella, and varicella vaccine ↳ first dose at 12-15 months, second close at 4-6 yrs