Background Enzymes that hydrolyze carbapenems
Includes members of most Ambler classes
Class A: KPC, IMI
Class B: NDM, IMP, VIM
Class C: AmpCs
Class D: OXA-48 Identification Screening is done by identifying isolates with decreased susceptibility to one or more carbapenems
A modified Hodge test can confirm the presence of a carbapenemase, but is no longer routinely recommended
Modified carbapenem inactivation method (mCIM)
Place meropenem disc in a suspension of the test isolate, and incubate at 35ºC for 4 hours
Remove disc, squeezing out excess fluid, and place on a lawn of susceptible Escherichia coli
Positive for carbapenemase if zone diameter is clear ≤15 mm (or pinpoint colonies up to 18 mm)
Negative if zone diameter is clear ≥19 mm
Indeterminate if clear diameter 16 to 18 mm, or pinpoint colonies ≥19 mm
EDTA-modified carbapenem inactivation method (eCIM)
Only done if mCIM is positive, to test for metallo-β-lactamases
As above for mCIM, but adds EDTA to the tube
Positive for metallo-β-lactamase if zone diameter increases ≥5 mm from mCIM
Ignore pinpoint colonies within any zones of inhibition in the eCIM
Rosco discs
Class A: attenuated by boronic acid
Class B: attenuated by diploconic acid
Class C: attenuated by both cloxacillin and boronic acid
Class D: not attenuated by boronic acid, diploconic acid, or cloxacillin
Needs special discs, or PCR testing Inhibitors Avibactam: active against ESBLs, AmpCs, KPC, and OXA-48, but not MBLs and other OXAs
Only inhibitor with some activity against class D (OXAs) Relebactam: active against ESBLs, AmpCs, and KPC, but not OXA-48, VIM, GES, or MBLsTazobactam: active against Pseudomonas Vaborbactam: active against KPC, but limited activity against MBLs and OXA-48, Pseudomonas Acinetobacter Specific Carbapenemases Management Directed by susceptibility testing
For ESBLs and AmpCs, consider:
For metallo-β-lactamases, consider:
For carbapenem-resistant Pseudomonas aeruginosa References
^ Jeanette W. P. Teo, My-Van La, Prabha Krishnan, Brenda Ang, Roland Jureen, Raymond T. P. Lin. Enterobacter cloacae producing an uncommon class A carbapenemase, IMI-1, from Singapore. Journal of Medical Microbiology . 2013;62(7):1086-1088. doi :10.1099/jmm.0.053363-0 .
