ESBL
One-Sentence Definition
ESBLs (extended-spectrum β-lactamases) are enzymes — chiefly class A TEM/SHV variants and CTX-M family — that hydrolyze penicillins, 1st–3rd generation cephalosporins, and aztreonam, usually remaining inhibited by clavulanate, and are typically plasmid-borne in Enterobacterales.
Simple Explanation
The bacterium makes a molecular scissors that cuts many cephalosporins. Carbapenems usually still work — until a carbapenemase arrives.
Detailed Scientific Explanation
| Family | Notes |
|---|---|
| CTX-M | Globally dominant community & hospital ESBL |
| TEM / SHV ESBL variants | Point-mutant expansions of older β-lactamases |
| OXA ESBLs | Less common; classification nuances |
Lab detection (conceptual):
- Ceftriaxone/cefotaxime/cefepime MIC elevation
- Clavulanate synergy (ESBL confirmatory logic)
- Molecular: blaCTX-M, blaTEM, blaSHV typing
- Chromosomal AmpC derepression can mimic — inhibitor profiles differ
Mobilization often via Integrons / Transposons and Insertion Sequences (e.g., ISEcp1–CTX-M) on conjugative Plasmids.
Mechanism
Serine β-lactamase expands active-site pocket → hydrolyzes oxyimino-cephalosporins → inactive drug; β-lactamase inhibitors (clavulanate, tazobactam, avibactam — spectrum differs) can block many class A ESBLs.
Clinical Importance
- Empiric cephalosporin failure in UTI, bacteremia, intra-abdominal infection.
- Carbapenems traditionally preferred for serious ESBL infections (stewardship nuance with piperacillin-tazobactam / newer agents — follow current evidence/guidelines).
- Infection control and One Health livestock links (One Health).
Research Importance
- Plasmid epidemiology of CTX-M-15 / CTX-M-14 etc.
- Feature of Bacterial GWAS and Machine Learning for AMR Prediction datasets.
Diagnostic Relevance
- Rapid molecular ESBL markers vs phenotypic confirmation — both used.
- WGS annotates bla context (AMR Gene Databases, Plasmid and Mobile Element Analysis).
AMR Relevance
Gateway MDR phenotype in Escherichia coli and Klebsiella pneumoniae; often co-travels with aminoglycoside and fluoroquinolone resistance cassettes.
Related Organisms
- Escherichia coli · Klebsiella pneumoniae · other Enterobacterales
Related Methods
Related MOCs
Learning Aids
Clinical Example
Example
Case: Pyelonephritis; E. coli resistant to ceftriaxone, susceptible to meropenem; clavulanate synergy positive; blaCTX-M-15 on IncF plasmid.
Question: ESBL or carbapenemase?
Answer: ESBL — carbapenem still active; escalate thoughtfully and plan step-down per guidelines.
Active Recall Questions
- Which ESBL family dominates globally today?
- How does ESBL differ from carbapenemase clinically?
- Name a mobile element classically linked to CTX-M mobilization.