Extended-spectrum beta-lactamase (ESBL)-producing organisms represent one of the largest infectious disease–related challenges in the intensive care unit (ICU) environment worldwide. The β-lactamase enzymes are capable of hydrolyzing the beta-lactam ring of penicillins and related compounds, rendering them inactive. To date, there have been hundreds of different types of β-lactamase enzymes identified. There have been many classification schemes proposed for β-lactamases. The classification initially introduced by Ambler in 1980 is based on the amino-acid sequence and recognizes four molecular classes designated A to D. This scheme is based on amino-acid similarity, with classes A, C, and D being serine-β-lactamases and class B being metallo-β-lactamases. The scheme proposed by Bush is a functional classification that defines four groups according to their substrate and inhibitor profiles.

The ESBL-producing organisms are noteworthy as they represent significant challenges in prevention, identification, and treatment. The ESBL enzyme is capable of hydrolyzing essentially all β-lactam antibiotics except carbapenems and cephamycins (cefotetan and cefoxitin). The first reports of ESBLs came in the early 1980s, after the development and widespread use of third-generation cephalosporins. Of note, ESBL enzymes are plasmid-mediated, rendering the DNA encoding the ESBL enzyme (as well as other types of resistance) easily transferable. Therefore, ESBL-producing organisms are frequently resistant to other classes of antibiotics suchas fluoroquinolones, aminoglycosides, and trimethoprim/sulfamethoxazole.