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Medical Microbiology
Skin Wounds and Infections
| Skin and Wound Infections | Features |
|---|---|
| Normal Skin Flora | w/in superficial epidermis and upper part of hair follicle; Stapylococcus, Micrococcus; Diptheroids; Fungi |
| Skin Staphylococci | Salt tolerant, universally present, prevents colonization; Staph epidermidis and the potential pathogen: S. aureus (on face/hands of nasal carrier; coagulase +) |
| Skin Diptheroids | Corynebacterium (Proprionibacterium acnes); G+, low virulance, associated with acne and body odor (their named b/c they resemble diptheria bacilli) |
| Skin Fungus | Malassezia furfur; yeast; lipophilic |
| P. acnes | anaerobic G+; grows in hair follicles; loves sebum that causes microcomedomes (black/whiteheads) |
| Folliculitus - minor infx of hair follicle | Staph aureus and Pseudomonas aeruginosa in areas of sweat gland activity and friction; Pseudomonas infx commonly ocur from hot tubs |
| Furuncle (boil; stye) | Staph. aureus attaches to follicle, multiplies and spreads down to involve the sebaceous gland; complication of acne vulgaris |
| Carbuncle | spread of furuncle infx to adjacent subcutaneous tissues; can lead to bacteremia |
| Chronic furunculosis | repeat boil episodes; delayed-type hypersensitivity is responsible for inflammation/necrosis; associated w/depressed host immunity (defected PMN fxn) |
| The Virulence of Staph Aureus | due to cell wall compenent PROTEIN A (prevents Ab binding and phagocytosis); Leukocidin destructive enzymes directed against host (Hyaluronidase - breaks tissues apart, proteases, lipases - helps hair follicle colinization) |
| STREPTOcoccal Impetigo | Group A Streptococcus (also staph aureus); characterized by PUS production on suferficial skin; yellow infected crusts weep; lymph nodes enlarge; Streptococcus pyogenes complication - glomerulonephritis |
| Acute Glomerulonephritis | comlication of Strep pyogenes pyoderma; immune complexes are deposited in glomeruli; inflammatory rxn causes tissue damage |
| Cellulitis | Grp A Strep and S. aureus (in infants - Haemophilus influenzae); acute inflammation of subcutaneous CT (fat) |
| Staphylococcal Scaled Skin Syndrome (SSSS) | Certain strains of S. aureus; production of EXFOLIATINS spreads thru blood to cause large areas of keratinized epidermis to detach; Secondary problems: dehydration and infection (Pseudomonas or Candida albicans) |
| Rocky Mountain Spotted Fever | Rickettsia rickettsii; from tick bite; sudden onset of flu-like symptoms and spotted rash spreads from extremities to body core; humans are accidental host |
| Lyme Disease | Borrelia borgdorferi; spirochetes from tick cause inflammatory rxn and spread thru circulation; flu-like symptoms, arthritis, chronic nervous system symptoms; ERYTHEMA MIGRANS...it moves... |
| Stage 1 Lyme Disease | erythema migrans on skin, lymph nodes |
| Stage 2 Lyme Disease | heart, CNS, PNS (like a Bell's Palsy) |
| Stage 3 Lyme Disease | Chronic arthritis; depresson; paralysis |
| Cat Scratch Disease | Bartonella hensalae; G- bacilli; vectors: domestic cats, cat flea, body louse (pediculus humanus coporis), ticks); febrile lympadenitis; rashes; conjunctivitis; encephalitis; prolonged fever |
| Dx and Tx of Cat Scratch Disease | serologic response to Bartonella henselae antigens; azithromycin or erythromycin...Associated with AIDS pts |
| Anthrax | Bacillus anthracis; spore-former G+ rod facultative anaerobe; non-hemolytic; non-mobile; contamination from infected livestockor animal products |
| 3 Routes of Acquisition | 1. Inoculation - 95% of cases through exposed skin; 2. Ingestion - rare in humans (herbivore route); 3. Inhalation - woolsorter's disease or terroristic |
| Cutaneous Anthrax | spore introduced through cut, abrasion, insect bite; incubates 2-7 days; papules surrounded by vesicles; vesicular ring ruptures; central black necrotic region forms |
| Scarlet Fever | Grp A Strep; rash w/ itchy bumps on face/neck, chest/back, then entire body; rash peels on 6th day; Strawberry Red Tongue |
| Varicella | dsDNA virus from herpes family; red bumps/blisters erupt into pustules that break and leak virus into fluid filled crusts that later heal; Respiratory transmission and spreads through blood; virus can enter sensory nerves (Shingles) |
| Varicella zoster | occurance of shingles related to decreased cell-mediated immunity (aging); replication in nerve cell nuclei and is carried by cytoplasm along dermatome; AIDS pts can have shingles all over body |
| Measles | ssRNA Rubeola virus of paramyxovirus family; viral envelope H and M projections (attachment/fusion); Respiratory transmission; replicates in upper respiratory epithelium, spreads to lymphoid tissue, then body; rash from viral replication in skin cells |
| Smallpox | dsDNA variola virus from poxviridase family; enveloped/brick-shape; Major (common/severe) and minor (milder, rare) forms |
| Smallpox - Variola Major | 1. ordinary - 90%; 2. modified - milder in vaccinated pts; 3. flat - rare/severe; 4. hemorrhagic -rare/severe; Last case in US 1949, in world 1977 |
| Smallpox symptoms | up to 17 days w/o symptoms, then flu-like for 2-4d followed by rash/pustules/scab; contagious from onset of rash till last scab falls off; no Tx; 30% die; ANY case now would be an emergency!! |
| Warts | Papillomaviruses; infection thru abrasions; nipple-like protrusions covered by skin or mucous membrane; virus replicates in nuclei deep in epidermis; Tx: freezing/cauterization/surgery |
| Superficial cutaneous mycoses | fungal skin infections; living tissue not invaded; only hair, nails, keratinized skin; lack of cellular response from host; no pathological changes elicited |
| Tinea capitus, barbae, axillaris, corporis, cruris, pedis | scalp, beard, armpit, body, groin, feet |
| Malassezia furfur | lipophilic...requiring oil from hair follicles; can cause a scaly rash, dandruff, tinea versicolor, seborrhoeic dermatitis |
| Tinea versicolor | Malassezia furfur; patchy scaliness with increased/decreased pigmentation in fair/dark-skinned individuals |
| Cutaneous mycoses | Candida (yeast) and Dermatophytosis (epidermophyton, microsporum, trichophyton); under moist conditions dermatophytes can invade keratinized structures via keratinase; don't grow at 37C; pathogenesis dependent on virulence and moisture |
| Ringworm - cutaneous | dermatophyte; red, scaly, lacy rings on skin; thick/brittle nails; patchy hair loss |
| Diaper Rash -cutaneous | Candida albicans; normal resident of human skin |
| Subcutaneous | chronic, localized infx of skin/subcut tissue d/t traumatic implantation of agent from soil saprophytes |
| Chromoblastomycosis - subcutaneous | dematiaceous fungi; rounded, sclerotic bodies |
| Phaeohyphomycosis - subcutaneous | dermaticaceous fungi; tissue morphology mycelial |
| Mycetoma - subcutaneous | Acremonium, Asperigillus; hard nodule which softens and ulcerates; discharge of viscous, purulent fluid |
| Rose Gardner's Disease - subcutaneous | Sporothrix schenckii (dimorphic fungus: mold/yeast forms); d/t puncture wounds in garden in upper extremitiy; chronic ulcer and enlarged lymph nodes |
| Psoriasis | Chronic inflammatory skin disorder; genetic; increased keratinocyte proliferation d/t shortened cell cycle; Plaque-type: scaly erythematous, pruritic on scalp, elbows, knees and more |
| Staphylococcal Wound Infections | G+; pyogenic - pus producing; grow in aerobic and anaerobic conditions and can spread to surrounding tissues to form abscesses; Virulence factors: coagulase, protein-A, alpha-toxin |
| Staph Protein A | binds IgG by Fc protein on immunoglobulin to inhibit phagocytosis |
| Staph alpha-toxin | used to attach to and porforate host cell membrane |
| Group A Streptococcal "Flesh Eaters" | Strep pyogenes; usually susceptible to penicillin; can progess to severe infx (pneumonia, meningitis, necrotizing fasciiis, strep toxic shock) |
| Strep toxins - Exotoxin A | pyogenic superantigen that causes toxic shock |
| Strep toxins - Exotoxin B | protease |
| Necrotizing Fasciitis | Strep. pyogenes; colonization and destruction of fatty tissues; fluid buildup/infx produces toxic products; Tx: Removal of diseased tissue/toxins |
| Pseudomonas aeruginosa | opportunistic pathogen; nosocomial infx, esp burn victims (some community acquired in pools, too); Forms biofilms in lungs of CF pts; difficult to Tx |
| Burns and Pseudomonas | G- rods, motile, facultative anaerobe (Nitrate final e acceptor); turns wound a GREEN color with a sweet smell; tissue damage prevents healing; septic shock from circulating PATHOGENS (not toxins like strep/staph) |
| Tetanus "lock-jaw" | Claustridium tetani; G+ spore-forming anaerobic; plasmid produces toxin; muscle spasm in jaw; pt can die from pneumonia when stomach contents is aspirated |
| Tetanus - tatanospasmin exotoxin | blocks inhibatory neurons for muscle contraction; continuous contraction ensues; |
| Tetanus - cause/Tx | puncture wounds; prevent via immunizations if inactivated tetanus toxoid; Tx: tetanus antitoxin (TIG - tetanus immune globulin); clean dead tissue, metranidazole |
| Gas Gangrene | Clostridium perfringens - grows in dead anaerobic tissue (clostridial myonecrosis); results from neglected wounds containing debride; black swelled/streched skin with leaky bloody/brown frothy fluid d/t gas production; Sx necessary to remove dead tissue |
| Clostridium perfrigens | G+ spore-forming obligate anaerobe; saphophytic (loves dead tissue); 20 different exotoxins (alpha (outer) and theta (inner) leave double hemolysis zone on blood agar) |
| Clostridium pefringens exotoxins - Alpha-toxin | necrotizing; lecithinase hydrolyzes lecithin and sphingomyelin (egg-yolk agar); hydrolyzes key components in cell membrane; RBCs, WBCs, platelets, fibroblasts, muscle cells; most important virulent factor |
| Clostridium perfringens exotoxins - Theta-toxin | alters capillary permeability; toxic to heart muscle; pore-forming; loss of cellular fluid |
| Bacterial bite wounds | Pasteurella multocida; G- rod, facultative anaerobe; causes fowl cholera; capsules are antiphagocytic and form abscesses; Tx with penicillin plus a b-lactamase inhibitor (amoxicillin) |
| Cutaneous Leishmaniasis | protozoan parasite Leishmania from sand fly bites; can cause localized ulcer/nodule |
| Scabies | Sarcoptes scabiei; mite burrows into epidermis and feeds/lays eggs for 1mo; rash from allergy forms; Dx by identifying mite; rash is itchy on hands btw fingers, under breasts and in genital areas |
| Staphylococcus epidermidis | little invasive ability; glycocalyx slime protects its colonies on catheters, etc; can get into blood and cause subacute bacterial enteritis in diabetic or cancer pts |
| Treatment of staph infx | penicillins, cephalosporins resistant to b-lactamase, MRSA - vancomycin or Synercid |
Created by:
bscaryp