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skin, muscle, blood

Lectures 22-23

coagulase test cuases clot formation in rabbit or human plasma. S. aureus positive for catalase and coagulase
S.aureus alpha toxin chromosomally encoded, low molecular weight protein, causes necrosis or death in experimental animals, causes mammalian cells to leak through pores formed by toxin
S. aureus pyogenic exotoxin causes toxic effects at sites remote from the site of infection
TSS toxin pyogenic exotoxin, absorption of toxin from local site, stimulates release of cytokines, direct toxic effects on endothelial cells. shock, diarrhea, rash, renal impairment, respiratory failure
S. aureus exfoliatins produced by some strains only, leads to intercellular splitting of the epidermis between spinosum and granulosum by disruption of intercellular junctions
staph cellulitis alternates between walling off and rapid extension of infection, infection of skin and soft tissues
impetigo found with group A strep in up to 30% of cases
wound infection can be from the patient's own strain or nosocomial strains spread by health workers practicing poor hygiene. Staph aureus most common
acalded skin syndrome due to staph toxin, absorbed into bloodstream, intraepidermal desquamation occurs at remote sites
coagulase negative staph normal commensals, normally lack major virulence factors of S. aureus (not beta hemolytic, grouped with normal flora),have become opportunistic due to medical devices, immunosuppression, and major surgeries
S. lugdunensis primary pathogen, causes occisional very serious infections (abscess formation, may be emerging)
Staph epidermidis produces extracellular polysaccharide, slime, or biofilm:provides adhesion to indwelling devices like catheters, atrificial heart valves, CSF shunts, hip replacements. In biofilm organisms are protected from phagocytosis& antibiotics, but get nutirents
clinical significance of coagulase negative staph likely to be significant if present in multiple blood cultures, intracellular gram+ cocci seen in gram stain, culture shows moderate to heavy numbers on culture plates from wound specimens. Less likely if very few positive numbers
clinical significance of CNS in catheter infections catheter tip is removed, rubbed over blood agar, and incubated. 15or more colonies of caogulase - staph is threshold
basic characteristics of strep part of normal flora (inhibit oral cavity, GIT, and genital tract), can be pathogenic in specific growth environments within the body. Classified based on hemolysis on blood agar
Group A toxin pyrogenic exotoxin, stimulates cytokine release causing multiple effects
Pharyngitis (group A) common bacterial infection in throat, spread by direct contact or aerosols
poststreptococcal sequalae rheumatic fever: inflammatory, ACCNE, heart valve damage Acute glomerulonephritis: lesions of glomeruli, 10 days after respiratory infection, Ag-Ab complexes
Group B strep (agalactiae) carried by up to 30% of women in normal vaginal flora, can be acquired by neonate in birth
viridans streptococci aplha hemolytic, refers to all others once S. pneumoniae has been ruled out, normalflora of mouth, gut, and moist skin. All can cause subacute bacterial endocarditis (mutans, miis, salivarius) detect with blood cultures, treat with penecillin
Strep mutans associated with dental carries
viridans on heart valve initially adhere to tiny imperfections on valve,usually sensitive to penecillin G if given for prolonged periods, penecillin prior to dental procedures in those with damaged valves is prophylaxis-->prevents endocarditis
Abiotrophia: nutritionally deficient strep will not grow on ordinary blood agar, causes bacterial endocarditis (difficult to detect unless lab adds a "feeder" colony or special nutrients to media)
Enterococcus gram+ cocci in chains, natural habitat in gut, non-hemolytic strep, group D, major pathogens: E. faecalis, E. faecium (resistant to ampicillin, more likely to be reistant to vancomycin)
enterococcus diseases opportunistic: after broad spectrum antibiotics, edocarditis, UTI, wound infections in intensive care units (usually as a mix with other bacteria like E.coli)
Corenybacterium gram positive rods, not acid fast, pleomorphic shape, pathogen: C. diptheria, opportunistic pathogen: C. ulcerans, C. jeikeium
c. diptheriae causes diptheria, impetigo like lesions, most common in tropics.
E. rhusoppathiae causes erysipeloid: painful slowly spreading skin lesion, follows traumatic inoculation of skin (fishermen, butchers, vets), treated with penicillin or erythromycin
anaerobic bacteria part of normal flora (in stool of colon, mouth, throat, upper GI, vagina, skin), require special antibiotics, must order an anaerobic culture
opportunistic anaerobic infections in tissues that have trauma, malignancy, inflammation, impaired blood supply, surgery, a foreign body
for cultures use: abscess fluid aspirates, surgically removed tissue, blood cultures
unacceptable specimens for anaerobic isolation superficially collected from skin and wounds
Clostridium perfringens toxin alpha toxin: main pathogenic factor (diffuses out killing all cells producin more necrotic growth areas for organism), theta toxin: toxic for heart and muscle capillaries, Enterotoxin: causes food poisoning
Lactobacillus colonies resemble alpha streptococci, normal vaginal flora, if replaced with mobiluncus vaginitis results
actinomyces long gram positive rods, often branching, no spores, acid fast. Serious chronic infections (uterus with IUD, aspiration pneumonia, abscesses). Pus=sulfur granule Israelli:most common in serious infection, "molar tooth" takes 4-8d to grow.
Propionibacterium acnes anaerobic coryneform, causes acne, opportunistic infections in prosthetic devices, part of mixed anaerobic infections
gram negative anaerobic rods bacteriodes fragilis: most common group: has capsule with antiphagocytic function, 10 species are penecillin resistant
Rickettsia gram- bacilli, intrcellular pathogen, reservoir in insect, causes fever with rash, host is infected by insect bite, systemic infection follows
Rocky Mountain Spotted Fever (rickettsia rickettsii) occurs in warmer months, most in children, history of tick bite, incubation period 2-10d (fever, headache, confusion, myalgia), rash is main feature (palm and soles), spreads from extremities to trunk, death in 25% w/out treatment, detection with Ab titer
Rickettsialpox urban disease cause by R. akari, transmitted by house mouse mite bite, benign self limiting illness, papulovesicle--> fever and rash, tetracycline effective
louse borne typhus fever Rickettsia prowazekii, disease of war and upheaval, transmitted by body louse, infected louse will die, but not before it infects others, defecates when it feeds--> deposits organisms near the bite wounds
Typhus fever symptoms 1-2 weeks after bite, fever, headache, myalgia, malaise, rash on trunk spreads to extremities, complications to CNS and heart, 10-60% mortality. Treat with tetracycline and chloramphenicol or louse control
Murine typhus Rickettsia typhi, disease of urban rodents, accidental transmission to man (bite of rat flea), disease similar to louse borne typhus, but complications and mortality are rare.
Created by: kamarsh



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