Staphylococci Flashcards
staphylococci morphology
gram positive in grape like clusters
facultative
diagnostic criteria for s. aureus
g+ clusters yellow catalse positive coagulase positive mannitol fermnatation pos DNase pos hemolysis pos resistance to novobiocin neg anaerobic growth pos
properties
protein A pos
teichoic acid pos
phage receptor pos
diagnostic criteria for s. epidermidis
g+ clusters white catalase pos coagulase neg mannitol fermnatation neg DNase neg hemolysis neg resistance to novobiocin neg anaerobic growth pos
properties
protein A neg
teichoic acid +
phage receptor neg
diagnostic criteria for s saprophyticus
g+ clusters white catalse positive coagulase neg mannitol fermnatation neg DNase neg hemolysis neg resistance to novobiocin pos anaerobic growth slowly
Properties
protein A neg
teichoic acid pos
phage receptor neg
s. aureus epi
found on skin and mucous membranes of normal individuals
colonizes w/ foreign bodies (catheters, drug addicts)
can be traced via DNA fingerprinting, ribotyping
s. aureus toxin mediated pathogenesis
toxin mediated-
contamination- food, tampon
food- enterotoxin
bacterial colonization- uses fibrinogen receptors
- toxic shock snydrome toxin
exfoliatins- staphylococcal scalded skin syndrome
s. aureus invasive pathogenesis
synthesizes adhesive molecules that bind to extracellular matrix (fibrinogen, fibronectin- found on damaged skin
produce toxins via lysis
- alpha toxin- lyse host cell membranes
- leukocidins
- proteases
- coagulase
- staphylokinase
- hyaluronidase
- lipase
how does s aureus evade host
protein A- binds host IgG on Fc receptors, binding on the wrong end
enterotoxins- T-cell superantigens
capsule- antiphagocytotic
Eap- impairs neutrophil recruitment
s aureus consequences
if contained by immune system- abscess
if not- bacteremia
s aureus toxin mediated syndromes
food poisioning- d/t enterotoxins- heat labile. many are superantigens (A and C). causes nausea, vomiting, and non bloody diarrhea
toxic shock syndrome- superantigen stimulates IL 1 2 and TNF. fever, rash, hypotension and shock
scalded skin syndrome
caused by exfoliatins A and B
superantigens
s aureus invasive syndromes
causes abscess and suppration
superficial-
red, vesicular lesions, folliculitis, boils, nail bed infections
deep seated
pneumonia, endocarditis, osteomyelitis, arthritis, abscess, meningitis, sepsis
s aureus treatment
absesses must be drained
synthetic penicillin- dicloxacillin, oxacillin
vanco- last resort
s epidermidis epi
gram + cocci
normal flora of skin
adhere to foreign bodies, opportunistic pathogens
neonates, renal failure, or immunocompromised pts susceptible
s epidermidis pathogenesis
colonize prosthetic surfaces efficiently- form biofilms
can become bactermic
s epidermidis syndromes
fever, pain, discomfort
later- bacteremia
