ESBL
Summary
ESBL (Extended-Spectrum Beta-Lactamase) refers to bacterial enzymes that confer resistance to penicillins, cephalosporins (including 3rd/4th generation), and aztreonam by hydrolyzing their beta-lactam ring. Commonly produced by Enterobacteriaceae (E. coli, Klebsiella pneumoniae), ESBL-producing organisms are a major cause of multidrug-resistant infections. Carbapenems (e.g., meropenem) are typically the treatment of choice.
Detail
ESBLs are plasmid-encoded enzymes (most commonly derived from mutations in TEM, SHV, or CTX-M beta-lactamases) that hydrolyze the beta-lactam ring of penicillins, cephalosporins (1st through 4th generation), and monobactams (aztreonam), rendering these antibiotics ineffective. They do NOT typically confer resistance to cephamycins (cefoxitin, cefotetan) or carbapenems, though co-resistance mechanisms can occur.
Pathophysiology: ESBL genes are often carried on plasmids alongside other resistance genes (e.g., aminoglycosides, fluoroquinolones), leading to multidrug-resistant phenotypes. This horizontal gene transfer facilitates rapid spread among Enterobacteriaceae, particularly E. coli and Klebsiella pneumoniae, though also seen in Proteus, Enterobacter, and other gram-negative rods.
Clinical significance: ESBL-producing organisms are a major concern in healthcare-associated infections, including UTIs, bacteremia, intra-abdominal infections, and pneumonia. Risk factors include prior antibiotic exposure (especially cephalosporins), hospitalization, indwelling devices, and travel to endemic regions. Detection requires laboratory confirmation via double-disk synergy testing or automated susceptibility testing showing resistance to ceftazidime/cefotaxime that is reversed by clavulanic acid.
Treatment: Carbapenems (meropenem, imipenem, ertapenem) are first-line therapy for serious ESBL infections due to their stability against these enzymes. Beta-lactam/beta-lactamase inhibitor combinations (piperacillin-tazobactam) show variable efficacy and are generally avoided for severe infections due to concerns about clinical failure despite in vitro susceptibility. Newer agents like ceftazidime-avibactam or cefiderocol may be used in select cases. Carbapenem overuse has led to emerging carbapenem-resistant Enterobacteriaceae (CRE), a critical public health threat.
Board relevance: Know that ESBL confers resistance to penicillins, cephalosporins, and aztreonam but spares carbapenems and cephamycins; understand mechanism (beta-lactamase enzyme hydrolysis) and first-line treatment (carbapenems).
Sources
- Sanford Guide to Antimicrobial Therapy
- Harrison's Principles of Internal Medicine
- First Aid for the USMLE Step 1
- Mandell's Principles and Practice of Infectious Diseases
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.