Carbapenemases: Difference between revisions

Revision as of 13:26, 12 September 2020

Background

Enzymes that hydrolyze carbapenems
Includes members of most Ambler classes
- Class A: KPC
- Class B: NDM, IMI, VIM
- Class D: OXA-48

Identification

Screening is done by identifying isolates with decreased susceptibility to one or more carbapenems
- Testing "not susceptible" to ertapenem is the most sensitive indicator
- Typically also resistant to third-generation cephalosporins, as well, with the exception of SME in Serratia marcescens and IMI
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

Management

Ceftazidime-avibactam (not active against metallo-β-lactamases)
Meropenem-vaborbactam (limited activity against metallo-β-lactamases and oxacillinases)
Colistin
Tigecycline

@@ Line 1: / Line 1: @@
-== Management ==
+== Background ==
+* Enzymes that hydrolyze [[carbapenems]]
-* [[Ceftazidime-avibactam]] (not active against metallo-β-lactamases)
+* Includes members of most Ambler classes
-* [[Meropenem-vaborbactam]] (limited activity against metallo-β-lactamases and oxacillinases)
+** Class A: KPC
-* [[Colistin]]
+** Class B: NDM, IMI, VIM
-* [[Tigecycline]]
+** Class D: OXA-48
+=== Identification ===
+* Screening is done by identifying isolates with decreased susceptibility to one or more [[carbapenems]]
+** Testing "not susceptible" to [[ertapenem]] is the most sensitive indicator
+** Typically also resistant to third-generation [[cephalosporins]], as well, with the exception of SME in [[Serratia marcescens]] and IMI
+* 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
+==Management==
+*[[Ceftazidime-avibactam]] (not active against metallo-β-lactamases)
+*[[Meropenem-vaborbactam]] (limited activity against metallo-β-lactamases and oxacillinases)
+*[[Colistin]]
+*[[Tigecycline]]
 [[Category:Gram-negative bacilli]]