2. Staphylococcus Flashcards by Samantha Boyer

Micrococcus habitat

Environment, food

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Rothia habitat

Mouth, URT

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Staph relationship to O2

Facultative anaerobes

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Staph tolerates —% salt

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Differentiates Staph from Strep

Catalase

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Function of protein A
Who has it?

SAUR

Binds the Fc of IgG. Prevents opsonization and phagocytosis.

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2 functions of catalase

Breaks down toxic end-products of glucose metabolism (H2O2)

Breaks down the myeloperoxidase system so organism can survive within WBC

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function of hyaluronidase and fibrinolysin

Breaks down connective tissue. Allows organism to move through the tissues.

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Superantigens

Stimulate T cells to produce a large burst of cytokines leading to an overwhelming inflammatory response and multi-disease and shock syndrome

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B-lactams work by binding to…

penicillin binding proteins (PBP)

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B-lactamase produced by —% of Staph now

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CA-MRSA is likely to produce this virulence factor

Panton-Valentine Leukocidin (PVL)

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Clinical effects of PVL

Causes severe skin infections and necrotizing pneumonia. Often fatal within 72 hours.

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2 types of coagulase and their respective test methods

Bound/clumping factor—Slide coag test

Free—Tube coag test

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———-, 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

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Saline control for slide coag test check for——

autoagglutination

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negative —- coag must be confirmed with —- coag

slide
tube

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—–% of SAUR may be false negative by slide coag test

10-15

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SNA that produces clumping factor but not free/extracellular coagulase

Slide pos (false), tube neg.

SLUG

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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

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Rare strains of SAUR can be tube coag negative because…

Naturally produce little/no coagulase

Produce staphylokinase, dissolving clot

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SNA that may be slide neg, tube pos.

SINT

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Staph latex detects…

bound coagulase
protein A

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Staph latex beads are coated with…

human plasma/fibrinogen
IgG to protein A

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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

toxin associated with impetigo

exfoliatin

---% of impetigo cases due to SAUR

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

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

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

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