6. Multi-Drug Resistant Organisms

Question 1

Combination therapy to treat Enterococcus infections?

Answer 1

Ampicillin-sulbactam
Amoxicillin-clavulanate
Piperacillin-tazobactam

Question 2

What 2 types organisms is the CarbaNP test for?

Answer 2

Enterobacteriaceae
Pseudomonas aeruginosa

that are I or R to 1+ carbapenem

Question 3

ESBL confirmation test

Answer 3

Phenotypic confirmatory test

Question 4

Often used against MRSA, but rapid development of resistance => not recommended for monotherapy

Answer 4

Rifampin

Question 5

Most common carbapenemase?

Answer 5

Class A (KPC)

Question 6

Test that predicts mecA-mediated resistance in S. aureus

Answer 6

30 ug cefoxitin disc

Question 7

Methicillin resistant Staphylococcus aureus are strains that have MICs to oxacillin = __ ug/mL.

Answer 7

4

Question 8

Difference between G+ and G- B-lactamases?

Answer 8

G+ = exoenzymes secreted by organism

G- = concentrated in periplasmic space; not secreted

Question 9

When is inducible B-lactamase resistance in staph tested for?

Answer 9

whenever a staph tests “S” to penicillin

Question 10

Next step after staph tests ‘S’ for pencillin?

Answer 10

Test for inducible B-lactamase

Question 11

3rd gen = R
1st gen = S
What does this suggest?

Answer 11

ESBL

Question 12

Patient screening for MRSA - appropriate anatomical sites?

Answer 12

• Anterior nares (nostrisl)
• Axillae (armpits)
• Wounds, drain sites

Question 13

Penicillin zone edge test ‘sharp zone edge’ interpretation?

‘Fuzzy zone dge’?

Answer 13

Sharp = B-lactamase production POS

Fuzzy = NEG

Question 14

MRSA strains are _____________: have both “S” and “R” subpopulations

Answer 14

hetero-resistant

Question 15

Purpose of 4% salt MHA plate

Answer 15

MRSA strains grow well at higher [salt] => pushes expression of mecA gene

Question 16

Used in the cefinase test for induced hyper beta lactamase production

Answer 16

1 ug oxacillin disc

Question 17

2 types of MRSA screening media?

Answer 17

MSAO - mannitol salt agar w/ oxacillin

• mannitol fermenters = possible MRSA = yellow
• CoNS = white/pink

Chromogenic agars

Question 18

4 penicillinase-labile penicillins

Answer 18

Penicillin
Amoxicillin
Ampicillin
Piperacillin

Question 19

Patient screening for VRE - appropriate anatomical sites?

Answer 19

• Stool, perineum/rectum
• Neck, groin (neonates)

Less common = urine, open wounds, drain sites

Question 20

Used in the screen test for oxacillin resistance in staph

Answer 20

MH agar w/ 4% NaCl and 6 ug/mL oxacillin

Question 21

S. aureus strains that are R to oxacillin but S to amoxicillin/clavulanic acid

Answer 21

BORSA

Question 22

Organism that shows some resistance to oxacillin (usually “I” MICs) are called…?

Answer 22

BORSA

Question 23

New subclass of cephalosporin w/ anti-MRSA activity

Answer 23

Ceftaroline

Question 24

3 types of VRE screening media?

Answer 24

Chromagar plates

BEAV - brown-black colonies w/ dark halo

VRE selective broth - look for evidence of black/grey growth, subculture to agar

Question 25

4 common B-lactamsae inhibitor combo drugs

Answer 25

Amoxicillin/clavulanic acid Ticaricillin/clavulanic acid Piperacillin/tazobactam Ampicillin/sulbactam

Question 26

Why should isolates of enterococci from sterile sites have nitrocefin beta-lactamase test done as well as routine KB susceptibility testing?

Answer 26

Resistance to ampicillin and penicillin due to B-lactamases cannot reliably be predicted by routine KB or MIC methods

Question 27

MRSA treatment alternatives - particularly if community-acquired and non-invasive

Answer 27

Tetracyclines, SXT

Question 28

3 penicillinase-stable (resistant to B-lactamase) penicillins

Answer 28

Oxacillin Cloxacillin Methicillin Nafcillin

Question 29

Detection of inducible AmpC B-lactamases?

Answer 29

Cefoxitin = primary screen

Question 30

How is low level vancomycin resistance in Enterococci detected?

Answer 30

BHI w/ 6ug/mL vancomycin (part of routine AST for all enterococci)

Question 31

3 class B carbapenemases

Answer 31

NDM-1 IMP-type VIM

Question 32

Test that must be done for all BORSA isolates?

Answer 32

B-lactamase test

Question 33

Beta lactamase test common uses what antimicrobial?

Answer 33

Nitrocefin

Question 34

Purpose of mCIM vs eCIM?

Answer 34

mCIM - detect carbapenemases eCIM - differentiates metallo-B-lactamases from serine carbapenemases (only interpreted if mCIM POS)

Question 35

Confirmation of inducible AmpC B-lactamases?

Answer 35

E-test AmpC strip => uses cefotetan (less sensitive than cefoxitin) Cefoxitin-cloxacillin double-disk synergy (CC-DDS) - cloxacillin inhibits AmpC B-lactamases

Question 36

The 4 drugs that may be used to screen for ESBL producers?

Answer 36

- Ceftazidime - Cefotaxime - Azthreonam - Ceftriaxone