Extended-spectrum beta-lactamases.

Extended-spectrum beta-lactamases (ESBLs) were discovered in Europe in the early 1980s after widespread use of broad-spectrum antibiotics. They are largely derivatives of 3 progenitor beta-lactamases that confer resistance to ampicillin in gram-negative bacteria and are now carried on plasmids. Substitutions at the active enzyme site of these progenitor enzymes at single or multiple amino sites have resulted in altered substrate affinities for ESBLs. Depending on the location of the substitution, susceptibility to broad-spectrum antibiotics is variably diminished. ESBLs are most commonly found in Klebsiella species and Escherichia coli, but also in other bacteria including Pseudomonas, Salmonella, Proteus, and Enterobacter species. The discovery of ESBLs in hospital and nursing-home outbreaks and their ability to be transferred to other bacterial species makes management and treatment of ESBLs of great medical concern.This article provides a review of ESBLs and their impact on patient care. Copyright 2002, Elsevier Science (USA). All rights reserved.