6. Multi-Drug Resistant Organisms Flashcards
Combination therapy to treat Enterococcus infections?
Ampicillin-sulbactam
Amoxicillin-clavulanate
Piperacillin-tazobactam
What 2 types organisms is the CarbaNP test for?
Enterobacteriaceae
Pseudomonas aeruginosa
that are I or R to 1+ carbapenem
ESBL confirmation test
Phenotypic confirmatory test
Often used against MRSA, but rapid development of resistance => not recommended for monotherapy
Rifampin
Most common carbapenemase?
Class A (KPC)
Test that predicts mecA-mediated resistance in S. aureus
30 ug cefoxitin disc
Methicillin resistant Staphylococcus aureus are strains that have MICs to oxacillin = __ ug/mL.
4
Difference between G+ and G- B-lactamases?
G+ = exoenzymes secreted by organism
G- = concentrated in periplasmic space; not secreted
When is inducible B-lactamase resistance in staph tested for?
whenever a staph tests “S” to penicillin
Next step after staph tests ‘S’ for pencillin?
Test for inducible B-lactamase
3rd gen = R
1st gen = S
What does this suggest?
ESBL
Patient screening for MRSA - appropriate anatomical sites?
- Anterior nares (nostrisl)
- Axillae (armpits)
- Wounds, drain sites
Penicillin zone edge test ‘sharp zone edge’ interpretation?
‘Fuzzy zone dge’?
Sharp = B-lactamase production POS
Fuzzy = NEG
MRSA strains are _____________: have both “S” and “R” subpopulations
hetero-resistant
Purpose of 4% salt MHA plate
MRSA strains grow well at higher [salt] => pushes expression of mecA gene
Used in the cefinase test for induced hyper beta lactamase production
1 ug oxacillin disc
2 types of MRSA screening media?
MSAO - mannitol salt agar w/ oxacillin
- mannitol fermenters = possible MRSA = yellow
- CoNS = white/pink
Chromogenic agars
4 penicillinase-labile penicillins
Penicillin
Amoxicillin
Ampicillin
Piperacillin
Patient screening for VRE - appropriate anatomical sites?
- Stool, perineum/rectum
- Neck, groin (neonates)
Less common = urine, open wounds, drain sites
Used in the screen test for oxacillin resistance in staph
MH agar w/ 4% NaCl and 6 ug/mL oxacillin
S. aureus strains that are R to oxacillin but S to amoxicillin/clavulanic acid
BORSA
Organism that shows some resistance to oxacillin (usually “I” MICs) are called…?
BORSA
New subclass of cephalosporin w/ anti-MRSA activity
Ceftaroline
3 types of VRE screening media?
Chromagar plates
BEAV - brown-black colonies w/ dark halo
VRE selective broth - look for evidence of black/grey growth, subculture to agar
4 common B-lactamsae inhibitor combo drugs
Amoxicillin/clavulanic acid
Ticaricillin/clavulanic acid
Piperacillin/tazobactam
Ampicillin/sulbactam
Why should isolates of enterococci from sterile sites have nitrocefin beta-lactamase test done as well as routine KB susceptibility testing?
Resistance to ampicillin and penicillin due to B-lactamases cannot reliably be predicted by routine KB or MIC methods
MRSA treatment alternatives - particularly if community-acquired and non-invasive
Tetracyclines, SXT
3 penicillinase-stable (resistant to B-lactamase) penicillins
Oxacillin
Cloxacillin
Methicillin
Nafcillin
Detection of inducible AmpC B-lactamases?
Cefoxitin = primary screen
How is low level vancomycin resistance in Enterococci detected?
BHI w/ 6ug/mL vancomycin (part of routine AST for all enterococci)
3 class B carbapenemases
NDM-1
IMP-type
VIM
Test that must be done for all BORSA isolates?
B-lactamase test
Beta lactamase test common uses what antimicrobial?
Nitrocefin
Purpose of mCIM vs eCIM?
mCIM - detect carbapenemases
eCIM - differentiates metallo-B-lactamases from serine carbapenemases (only interpreted if mCIM POS)
Confirmation of inducible AmpC B-lactamases?
E-test AmpC strip => uses cefotetan (less sensitive than cefoxitin)
Cefoxitin-cloxacillin double-disk synergy (CC-DDS)
- cloxacillin inhibits AmpC B-lactamases
The 4 drugs that may be used to screen for ESBL producers?
- Ceftazidime
- Cefotaxime
- Azthreonam
- Ceftriaxone
