Clinical Review

Recent developments in β lactamases and extended spectrum β lactamases

BMJ 2003; 327 doi: (Published 20 November 2003) Cite this as: BMJ 2003;327:1209
  1. Joumana N Samaha-Kfoury, specialist in infectious diseases1,
  2. George F Araj (, director of clinical microbiology1
  1. Department of Pathology and Laboratory Medicine, American University of Beirut Medical Center, PO Box 113-6044, Beirut, Lebanon
  1. Correspondence to: G F Araj
  • Accepted 9 September 2003

Resistance to β lactam antibiotics is an increasing problem worldwide. This review describes the classification and mechanism of action of βlactamases and the options available for detecting, treating, and controlling extended spectrum β lactamases


βlactam antimicrobial agents are the most common treatment for bacterial infections (table 1).1 Rates of bacterial resistance to antimicrobial agents are increasing worldwide, including in Lebanon.2 Production of β lactamases is the most common mechanism of bacterial resistance (table 2).1 3 These enzymes are numerous, and they mutate continuously in response to the heavy pressure of antibiotic use, leading to the development of extended spectrum β lactamases (ESBLs).4 Examples are the mutated TEM and SHV genes, mainly found in strains of Escherichia coli and Klebsiella pneumoniae respectively. Infections with ESBL producing bacterial strains are encountered singly or in outbreaks, especially in critical care units in hospitals, resulting in increasing costs of treatment and prolonged hospital stays. We aim to present a simplified review of this highly complex subject, in the hope that it will guide the practising physician in appropriate decisions relating to the use of β lactams in patient care.

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Table 1

Groups and examples of β lactam antimicrobial agents

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Table 2

Antimicrobial agents, their modes of action, and the corresponding mechanisms of bacterial resistance

Sources and selection criteria

We examined new information from the most recent relevant literature retrieved from PubMed and the internet.

Groups and mechanisms of action of β lactams

The β lactams are a family of antimicrobial agents consisting of four major groups: penicillins, cephalosporins, monobactams, and carbapenems (table 1). They all have a β lactam ring, which can be hydrolysed by β lactamases. The groups differ from each other by additional rings (thiazolidine ring for penicillins, cephem nucleus for cephalosporins, none for monobactams, double ring structure for carbapenems). The various antibiotics in each group differ by the nature of one …

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