staphylococcus Flashcards
microscopic evaluation of s. aureus
staphyle - bunch of grapes; coccus - berries
grows in clusters, pairs, short chains
G+ cocci with low G+C content
non-spore forming, non-motile
heat resistant
yellow CFU on blood agar, beta-hemolytic auereus = golden
general properties of S. aureus
catalase, lipase, DNAse, coagulase +, mannitol fermenter
facultative anaerobe
ribotol-type teichoic acid
re-emerging as an important human pathogen due to rapid development of antimicrobial resistance and increased use of indwelling medical devices.
S. aureus diseases
skin inflammation impetigo SSSS nectrotizing fasciitis osteomyelitis endocarditis keratitis indwelling medical device infection TSS food poisoning pneumonia septicemia pyopneumothorax empyema
TSS pathogenesis
ability of pyrogenic exotoxins to be superantigens; cause sustained release of TNF and IL-1 from macrophages; cause interferon-gamma and IL-2 from CD4+ cells; enhance host susceptibility to LPS; binds endothelial cells and may enhance capillary leakage
how many people killed as result of s. auerus
40,000 people/yr in USA
infections cost 10.7 billion/yr
what makes s. aureus a formidable pathogen?
s. auerus is the agent of numerous types of infecitons, syndromes, and toxinosis; produces numerous types of virulence factors that are coordinately regulated by adaptive systems; has the ability to persist in host cells and biofilms; pan-antibotic resistant strains of s. aureus have emerged; s. aureus highjacks our immune response to do its bidding
virulence factors of s. auerus
aherence - polysaccharid A; MSCRAMMS; coagulase
damage to host
5 cytotoxins
exfoliate toxin - SSSS
enterotoxins - TSS; food poisoning
TSST
immunoavoidance
leukocidin and gamma hemolusin
capsule
protein A
biofilms
extracellular enzymes
coagulase
lipase
hyaluronidase
staphylokinase
laboratory diagnosis
specimens vary with disease process; gram stains on direct specimens; culture and identifaciton (gram positive cocci in clusters, catalase positive, coagulase positive); spa typing (protein A sequence); MLST
prevention and control
isolation of MRSA patients; proper refrigeration of food; protect patients from acquiring infection; eliminate carrier state with oral antibiotic and/or a topical anti-staphylococcal drug like mupirocin
s. aureus spread
direct contact, aerosols, contaminated food
infections are either
toxin mediated (food poisoning, TSS, SSSS) invasive (utilizes the array of virulence factors to cause disease)
staphylococcus epidermidis
normal flora of skin, nose, throat
can produce slime
causes opportunistic nosocomial infections
produces disseminated disease with multiple abscesses