Carbapenemases: Difference between revisions
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== Background == |
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* Enzymes that hydrolyze [[carbapenems]] |
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* Includes members of most Ambler classes |
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** Class A: KPC |
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** Class B: NDM, IMI, VIM |
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** Class D: OXA-48 |
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=== Identification === |
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* Screening is done by identifying isolates with decreased susceptibility to one or more [[carbapenems]] |
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** Testing "not susceptible" to [[ertapenem]] is the most sensitive indicator |
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** Typically also resistant to third-generation [[cephalosporins]], as well, with the exception of SME in [[Serratia marcescens]] and IMI |
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* A [[modified Hodge test]] can confirm the presence of a carbapenemase, but is no longer routinely recommended |
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* Modified carbapenem inactivation method (mCIM) |
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** Place meropenem disc in a suspension of the test isolate, and incubate at 35ºC for 4 hours |
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** Remove disc, squeezing out excess fluid, and place on a lawn of susceptible [[Escherichia coli]] |
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** Positive for carbapenemase if zone diameter is clear ≤15 mm (or pinpoint colonies up to 18 mm) |
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** Negative if zone diameter is clear ≥19 mm |
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** Indeterminate if clear diameter 16 to 18 mm, or pinpoint colonies ≥19 mm |
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* EDTA-modified carbapenem inactivation method (eCIM) |
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** Only done if mCIM is positive, to test for metallo-β-lactamases |
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** As above for mCIM, but adds EDTA to the tube |
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** Positive for metallo-β-lactamase if zone diameter increases ≥5 mm from mCIM |
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*** Ignore pinpoint colonies within any zones of inhibition in the eCIM |
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==Management== |
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[[Category:Gram-negative bacilli]] |
[[Category:Gram-negative bacilli]] |
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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
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.
