Catalast-Positive GPCs (chapter 14)

Question 1

Catalase pos GPCs (4 genera)

Answer 1

Staphylococci
Micrococci
Rothia (formerly Stomatococcus)
Planococcus

Question 2

Catalase neg GPCs (6 genera)

Answer 2

Streptococci
Aerococci
Enterococci
Leuconostoc
Pediococcus
Gemella

Question 3

catalase reaction

Answer 3

3% H2O2 –> O2 + H2O

Question 4

Other catalase pos organisms

Answer 4

Liseteria
Diphtheroids
(blood causes false pos)

Question 5

Coagulase positive gpc

Answer 5

Staph aureus

Question 6

coagulase neg GPC

Answer 6

Coag-neg staph (S. lugdunensis, S. intermedius, S. hyicus, S. schleiferi)
Micrococcus
Rothia
Planococcus

Question 7

tests for bound coagulase (clotting factor)

Answer 7

slide method

Question 8

tests for free coagulase

Answer 8

tube method

Question 9

What organism causes a positive reaction in both positive and negative coagulase wells?

Answer 9

Staph saprophyticus

Question 10

What substrate is used in coagulase test?

Answer 10

Rabbit serum

Question 11

How does coagulase test work?

Answer 11

Protein A reacts with antibody-coated latex beads and causes clumping

Question 12

Positive reaction for:
Tube coagulase =
Slide coagulase =

Answer 12

tube: Clot in tube in less than 4 hours (may look neg after 4 hours due to fibrinolysin)
slide: clumps within 10 seconds

Question 13

Staph Aureus virulence factors (9)

Answer 13

coagulase
Alpha toxin
enterotoxins
capsular antigen
penicillinase (beta-lactamase)
TSST 1
hyaluronidase
Exfoliatin
protein A

Question 14

Coagulase (SA virulence factor)

Answer 14

enhances evasion & survival, coats PMNs with fibrin, protects bac from phagocytosis. Bound and free forms.

Question 15

alpha toxin (SA virulence factor)

Answer 15

disrupts smooth muscle in blood vessels.
Toxic to RBCs, WBCs, plts & hepatocytes.
Demonecrotic action- breaks down cell membrane

Question 16

Thanks to alpha toxin, SA infections are often ____ and ____

Answer 16

inflammatory, necrotic

Question 17

Enterotoxins (SA virulence factor)

Answer 17

resistant to hydrolysis by gastric and intestinal enzymes. Often found in milk products. Associated with psuedomembranous colitis & TSS. Gastroenteritis, food poisoning.

Question 18

capsular antigen (SA virulence factor)

Answer 18

inhibits phagocytosis, creates biofilm.

Extreme cause of virulence. Allows bacteria to cling to inorganic surfaces & avoid effects of Abx.

Question 19

Penicillinase (SA virulence factor)

Answer 19

(beta-lactamase) Destroys beta-lactams by hydrolysis before drug can bind to PBPs in cell membrane

Question 20

TSST 1 (SA virulence factor)

Answer 20

(pyrogenic exotoxin C)

superantigen- makes t cells produce cytokines that cause major systemic events.

Question 21

most common TSST

Answer 21

Enterotoxin F; causes fever, low BP, loss of skin

Question 22

in TSS & SSS, infection _______, but toxins ________

Answer 22

localized, throughout body

Question 23

Hyaluronidase (SA virulence factor)

Answer 23

enhances evasion & survival in tissues. Aids in spread of infection

Question 24

Exfoliatin (SA virulence factor)

Answer 24

Exotoxin, causes SSS. Serine protease.

Caused extensive sloughing of skin, usually in infants. Burn-like effects with large, watery blisters.

Question 25

Protein A (SA virulence factor)

Answer 25

anti-phagocytic surface protein, bound to cytoplasmic membrane. High affinity for IgG & complement. Provides a mechanism for bac to bind to immune molecules, decreasing clearance from infection site.

Question 26

Staph epi and saprophyticus are differentiated by:

Answer 26

Novobiocin

Question 27

staph epi is Novobiocin _____

Answer 27

sensitive

Question 28

Staph saprophyticus is novobiocin _______

Answer 28

reisistant

Question 29

3 things that help differentiate Micrococcus from staphylococcus

Answer 29

Microdase Lysostaphin Bacitracin

Question 30

Micrococcus is lysostaphin _______

Answer 30

resistant

Question 31

Micrococcus is bacitracin _______

Answer 31

sensitive

Question 32

staph is bacitracin _________

Answer 32

reisistant

Question 33

virulence factors of Staph epi

Answer 33

``` biofilm production (exopolysaccharide) mecA gene/Abx resistance ```

Question 34

Micrococcus environmental requirement

Answer 34

strict aerobe

Question 35

Modified oxidase test

Answer 35

Use on bright yellow colonies (micrococcus suspected) Colonies should be 18 to 24 hours old Tests for cytochrome C production, blue color reaction within 2 minutes.

Question 36

Micrococcus treatment

Answer 36

no guidelines exist, usually susceptible to beta-lactams

Question 37

Bacitracin test

Answer 37

0.5 McFarland suspension plated to BAP, topped with 0.04-U Bacitracin disk. Incubate for 24 hours. Zone of 10 or more = susceptible, think micrococcus. Staph typically resistant- no zone of inhibition

Question 38

D test

Answer 38

0.5 MF suspension, Mueller Hinton plate Used to see if clinda can be reported as susceptible (negative D test) Erythromycin & Clinda disks placed 15 mm apart (12 mm for strep) and incubated overnight. positive test = clinda resistant

Question 39

MRSA MIC results

Answer 39

Methicillin >8 Oxacillin >4 (resistance to oxacillin indicates resistance to methicillin, all beta-lactams, clindamycins, gentamycin, cephalosporin)

Question 40

Mannitol Salt Agar

Answer 40

Selective for some Staph 7.5% Nacl Mannitol & phenol red (pH indicator) *Fermentation of mannitol turns agar yellow

Question 41

MRSA chromagar

Answer 41

Positive = denim blue color change after 24 hour incubation

Question 42

PBP2a test

Answer 42

Rapid immunochromatographic qualitative assay for detection of PBP2a Used on direct SA isolates to detect MRSA (if pt not previously identified as having MRSA)

Question 43

Limitation/consideration of PBP2a test

Answer 43

Only test on SA isolates, other staph species could be positive

Question 44

HA-MRSA often:

Answer 44

multi-drug resistant, including oxacillin

Question 45

CA-MRSA infections

Answer 45

Skin infections, boils

Question 46

CA-MRSA sensitive to

Answer 46

non-penicillins (previously) SXT, clindamycin, ciprofloxacin, tetracycline, vanco, linezolid or daptomycin **more sensitive to non-betalactams than HA strains

Question 47

Daptomycin

Answer 47

IV only, not for respiratory infections- inhibited by lung surfactancts

Question 48

Vanco susceptibilities on vitek

Answer 48

``` susceptible = 2 or less intermediate = 4-8 resistant = 16 or higher ```

Question 49

VRSA mechanism

Answer 49

plasmid-mediated transfer of vanA gene confers vanco resistance

Question 50

VISA mechanism

Answer 50

unusually thickened cell wall, increased drug bound on wall from dipeptides, drug doesn't affect cell as much.

Question 51

VISA/VRSA treatment

Answer 51

Daptomycin or Linezolid

Question 52

Linezolid

Answer 52

IV or oral Abx, can use for respiratory infections