2. Staphylococcus Flashcards
Micrococcus habitat
Environment, food
Rothia habitat
Mouth, URT
Staph relationship to O2
Facultative anaerobes
Staph tolerates —% salt
10
Differentiates Staph from Strep
Catalase
Function of protein A
Who has it?
SAUR
Binds the Fc of IgG. Prevents opsonization and phagocytosis.
2 functions of catalase
Breaks down toxic end-products of glucose metabolism (H2O2)
Breaks down the myeloperoxidase system so organism can survive within WBC
function of hyaluronidase and fibrinolysin
Breaks down connective tissue. Allows organism to move through the tissues.
Superantigens
Stimulate T cells to produce a large burst of cytokines leading to an overwhelming inflammatory response and multi-disease and shock syndrome
B-lactams work by binding to…
penicillin binding proteins (PBP)
B-lactamase produced by —% of Staph now
90
CA-MRSA is likely to produce this virulence factor
Panton-Valentine Leukocidin (PVL)
Clinical effects of PVL
Causes severe skin infections and necrotizing pneumonia. Often fatal within 72 hours.
2 types of coagulase and their respective test methods
Bound/clumping factor—Slide coag test
Free—Tube coag test
———-, present in plasma, reacts with bound coagulase, ——- forms and coats the cocci causing them to…..
Fibrinogen, present in plasma, reacts with bound coagulase, fibrin forms and coats the cocci causing them to clump together
Saline control for slide coag test check for——
autoagglutination
negative —- coag must be confirmed with —- coag
slide
tube
—–% of SAUR may be false negative by slide coag test
10-15
SNA that produces clumping factor but not free/extracellular coagulase
Slide pos (false), tube neg.
SLUG
Free coagulase activates a ———– which is modified into a ———– molecule. The molecule then reacts with fibrinogen to produce a fibrin clot.
Free coagulase activates a plasma coagulase reacting factor (CFR) which is modified into a thrombin like (TL) molecule. The TL molecule then reacts with fibrinogen to produce a fibrin clot
Rare strains of SAUR can be tube coag negative because…
Naturally produce little/no coagulase
Produce staphylokinase, dissolving clot
SNA that may be slide neg, tube pos.
SINT
Staph latex detects…
bound coagulase
protein A
Staph latex beads are coated with…
human plasma/fibrinogen
IgG to protein A
Staph latex false Pos organisms
SSAP
MLUT
Staph latex false neg
MRSA
capsule - masks clumping factor, protein A
Requires more expensive test, including Ab against capsule.
Commercial ID systems ideal for Staph…
from sterile specimens like blood
molecular methods of ID most useful for…
epidemiology studies
outbreak investigations
MSA salt conc.
7.5%
About ——-% of healthy individuals are colonized with SAUR in the nose and/or perianal region
25-35
clinical sign of direct SAUR invasion
pyogenic
blood cultures for osteomyelitis positive in —-% of cases
50
toxin associated with impetigo
exfoliatin
—% of impetigo cases due to SAUR
90
susceptibility testing done on all Staph
oxacillin/methicillin
vancomycin
most common SNA
SEPI
Most labs do not ID down to SNA species, except when…
From normally sterile site
From artifical device
1 positive SNA blood bottle per 6 =
2+ positive SNA bottles per 6 =
contaminant
pathogen
Fluorescent bright white gamma colonies from urine
SSAP
SSAP is coag —– and staph latex ——
negative
possibly weak positive (unsure why)
organism we use novobiocin testing for
intrinsically resistant
SSAP
SSAP zone of novobiocin inhibition should be ≤ —- mm
12
modified oxidase test distinguishes….
Micrococcus
blue positive
modified oxidase tests for organism’s ability to make ——–
cytochrome c oxidases
No valid method for susceptibility testing
SSAP
MLUT
Rothia has no growth in —% salt
5%
S. aureus of dogs
SINT
Could falsely report as MRSA due to tube coag positive and PPB2a latex positive
SINT
Double zone of beta hemolysis
SINT
Can break through MSA or chromogenic agar
SINT
PYR necessary to distinguish SAUR (neg) from…
SINT
SLUG
aggressive, destructive skin and soft tissue disease
SLUG
SNA sensitive to all antibiotics, which can distinguish it from SAUR
SLUG
Slide coag pos, latex pos, but susceptible to all antibiotics
SLUG
function of PBP
produce enzymes essential in producing and maintaining the peptidoglycan layer for the gram-positive cell wall
B-lactamase-resistant drugs
Methicillin, nafcillin, and oxacillin
how did MRSA “learn” to resist the B-lactamase-resistant drugs?
mecA
makes new PBP2a
SNA with potential to be methicillin R
SINT
synergetic drugs #1
function
examples
irreversible inhibition of beta-lactamase
Sulbactam, clavulanic acid and tazobactam
Ampicillin/sulbactam (Unasyn)
Amoxicillin/clavulinic acid (Augmentin)
Piperacillin/tazobactam (Zosyn)
synergistic drugs
Daptomycin, linezolid, tigecycline, minocycline, quinupristin/dalfopristin and telavancin
new drugs held in reserve for MDR strains—even R to vanc.
Vancomycin (glycopeptide) intermediate (VISA/GISA) cause
unusually thick cell wall that blocks vancomycin, which is very large in size
VISA morphology
small colonies
how did VRSA arise?
MRSA obtained the vanA gene for vancomycin resistance from VRE
—- cases of VRSA in US so far
16
linezolid, daptomycin, telavancin, ceftaroline, tigecycline, minocycline or quinupristin-dalfopristin
used to tx VRSA
R to erythromycin, S to clindamycin indicates organism does NOT have….
but it COULD have…
The constitutive erm gene (Always turned on); Resistance due to efflux (Always turned on)
Inducible erm
E/CC test for inducible erm
D test
now used to predict resistance due to mecA gene
better inducer than oxicillin
cefoxitin
Weak/false positive for catalase
Enterococcus
pseudocatalase
Tube coag false negative cause
Fibrinolysin
staph latex can only be used to test which organisms?
Cat + GPCs
indicator in MSA
phenol red
present in chromogenic agar to select for MRSA
cefoxitin
CO2 creates false ——- results on chromogenic agar
negative
Rothia vs Staph
Rothia does not grow in 5% salt
SNA gives POS tube coagulase
SINT
SNA gives POS slide coagulase
SLUG
SSAP and Novobiocin
Resistant
Distinguish SAUR from SINT and SLUG
PYR is neg for SAUR
Bile POS, salt NEG
SGAL
