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26 Cards in this Set
- Front
- Back
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MRSA
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S. aureus that has developed antibiotic resistance to a wide variety of antibiotics
this includes all penicillins including methicillin and other beta-lactamase resistant antibiotics |
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staphylococci (bunch of grapes) cause suppurative diseases such as
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carbuncle
furuncle osteomyelitis deep tissue abscesses wound infections pneumonia empyema pericarditis endocarditis meningitis purulent arthritis |
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SA are common following
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breaks in the skin
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MRSA is commonly seen in
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hospitals and athletic events (extensive skin abrasions esp in wrestling and football)
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MoA of MRSA
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occur by organisms acquiring SA cassette - a large mobile genetic element
SCC mec which carries mecA gene gene product is a penicillin binding protein that has little affinity for beta-lactam rings |
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dangers associated with MRSA
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significantly elevated mortality rate over those infected with methicillin sensitive SA (MSSA)
fivefold elevated death rate in people infected with MRSA as opposed to people infected with MSSA almost 50% higher in MRSA infected individuals as opposed to MSSA infected individuals |
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SA colonization
where is it often found? |
anterior portion of nares
on the skin enter through breaks in the skin, urinary tract, lungs, indwelling manmade devices like urinary catheters healthy individuals can carry MRSA around their nares for weeks or years |
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what is most commonly used to tx MRSA?
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vancomycin
another is teicoplanin-structural analogue of vancomycin but less toxic |
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vancomycin and teicoplanin is usually given by
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IV
some new SA strains have been isolated that show some resistance to vancomycin and teicoplanin |
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antibiotics that are ysed against vancomycin/teicoplanin resistant SA include:
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dapto mycin
linexolid tigecycline |
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protection against MRSA (3)
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1. alcohols (ethanol or methanol) can be used to kill MRSA on surfaces
2. quarternary ammonium compounds along with alcohols increase time of effectiveness of alcohol 3. wash hands with soap or alcohol is best way to prevent spread of MRSA |
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MRSA epidemiology
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1/3 of world population carries SA
immunocompromised at risk 20% of IV drug users MRSA outside hospital is Community Acquired |
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CA-MRSA vs nosocomial MRSA
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different genetic backgrounds and Ab sensitivity
CA-MRSA are most resistant to beta-lactam antibiotics, more susceptible than hospital acquired MRSA CA-MRSA is cross between easily treated SA and MRSA from hospital |
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SA toxins include
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leukocidin
enterotoxins exfoliatin toxic shock syndrome toxin number 1 |
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hemolysins
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alpha, beta, gamma delta
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alpha toxin
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dermonecrotic
administered subcutaneously to rabbits and is lethal in mice and rabbites when given intravenously |
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beta toxin is a
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sphingomyelinase responsible for hot-cold reaction
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gamma hemolysin
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not well characterized
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delta hemolytic
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phospholipase
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Panton-Valentine leukocidin
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act by same kind of leukocytic degranulation causd by streptolysins O and S
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Staphylococcal enterotoxins (A, B,C1, C2, D, E, G, H, I)
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proteins of MW 35,000
cause emesis and diarrhea |
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exfoliatin
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heat stable
acid labile responsible for staphylococcal scalded skin syndrome in infants called Ritter's disease in enonates 2 distinct forms of exfoliatin toxin (ETA and ETB) ETA: heat stable and gene is chromosomal ETB is heat labile and plasma-mediated exposure to toxins is followed by splitting of intracellular bridges (desmosomes) in stratum granulosum epidermis |
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extracellular enzymes
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coagulase - 7 immunological distinct
elaborate a number of EC enzymes: staphylokinase lipases hyaluronidase DNAse |
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cellular antigens
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polysaccharides A (ribitol phosphate teichoic acid)
B (glycerol phosphate techoic acid) that determine immunological specificies of S aereus and S. epidermidis Protein A or agglutinogen A - small basic protein which reacts with Fc fragment of mammalian IgG; ANTIPHAGOCYTIC |
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differences in virulence factors between MRSA and MSSA
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same viulence factors if not more in MRSA
enterotoxin A produced by MRSA is not same as MSSA no difference in ability of PMNs to phagocytize MRSA and MSSA there is not correlation between PVL And PMN lysis |
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wat is associated with tissue necrosis?
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Panton Valentine leukocidin (PVL)
severe necrotizing penumonia-carried gene for PVL |
