Carbapenemases
One-Sentence Definition
Carbapenemases are β-lactamases that hydrolyze carbapenems (and usually many other β-lactams), turning last-line agents ineffective; major families include KPC, NDM/VIM/IMP (MBLs), and OXA-48-like enzymes, typically mobile on plasmids.
Simple Explanation
These enzymes eat carbapenems — the drugs kept for the toughest Gram-negative infections — and they hitchhike between bacteria on plasmids.
Detailed Scientific Explanation
| Family | Ambler class | Key trait | Classic hosts |
|---|---|---|---|
| KPC | A | Inhibited by avibactam/vaborbactam (usually) | Klebsiella, other Enterobacterales |
| NDM, VIM, IMP | B (MBL) | Zinc-dependent; not inhibited by clavulanate/avibactam | Global Enterobacterales; Pseudomonas (VIM) |
| OXA-48-like | D | Weak carbapenemase, strong penicillins; hard to detect | Enterobacterales |
| SME, IMI, GES variants | A (less common) | Species-specific patterns | Varied |
Detection layers:
- Meropenem MIC / carbapenem inactivation assays
- Inhibitor/EDTA profiles (MBL hints)
- Molecular PCR / WGS (blaKPC, blaNDM, …)
- Plasmid typing for hospital epi
Mechanism
Enzyme hydrolyzes β-lactam ring of carbapenems → inactive drug. Class B needs Zn²⁺; class A/D use serine chemistry. Porin loss + efflux can raise carbapenem MIC without a carbapenemase — genotype clarifies.
Clinical Importance
- Defines CRE (carbapenem-resistant Enterobacterales) treatment pathway: ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, cefiderocol, colistin, tigecycline — family-dependent.
- MBLs need different regimens than KPC.
- Contact precautions, screening in outbreaks.
Research Importance
- Global plasmid epidemics (IncX3–NDM, etc.).
- AI/genomic prediction targets (Machine Learning for AMR Prediction, Plasmid Host Attribution with ML).
Diagnostic Relevance
- Never rely on “carbapenem R” alone — identify the enzyme class when possible.
- WGS + AMR Gene Databases for surveillance; phenotypic AST still guides therapy.
AMR Relevance
Highest-priority Gram-negative AMR. Core of ESKAPE Pathogens hospital risk; often stacked with ESBL and aminoglycoside genes on the same Plasmid.
Related Organisms
- Klebsiella pneumoniae · Escherichia coli · Pseudomonas aeruginosa · Acinetobacter baumannii (OXA carbapenemases common)
Related Methods
- Antimicrobial Susceptibility Testing · PCR · Whole-Genome Sequencing · Plasmid and Mobile Element Analysis
Related MOCs
Learning Aids
Clinical Example
Example
Case: K. pneumoniae meropenem MIC ≥16; PCR blaNDM-1 positive; ceftazidime-avibactam inactive in vitro.
Question: Why might avibactam combinations fail?
Answer: NDM is a metallo-β-lactamase — serine-β-lactamase inhibitors like avibactam do not restore activity; need MBL-active strategies per guidelines.
Active Recall Questions
- KPC vs NDM — which is an MBL?
- Why is OXA-48 easy to miss in the lab?
- Can porin loss raise carbapenem MIC without a carbapenemase gene?