Extended-spectrum β-lactamases (ESBLs) are enzymes hydrolyzing most penicillins and cephalosporins, including oxyiminoβ-lactam compunds but not cephamycins and carbapenems. Most ESBLs belong to the Amber class A of β-lactamases and are inhibited by β-lactamases inhibitors: clavulanic acid, sulbatam and tazobactam. ESBL production has been observed mostly in Enterobacteriaceae, particularly Escherichia coli and Klebsiella pnuemoniae, but all other clinically-relevant Enterobacteriaceae species are also common ESBL-producers. In many areas, ESBL detection and characterization is recommended or mandatory for infection control purpose.ESBL detection involves two important steps. The first is a screening test with an indicator cephalosporin which looks for resistance or diminished susceptibility, thus identifying isolates likely to be harboring ESBLs. The second step is a confirmation test which evaluates the synergy between an oxyimino cephalosporin and clavulanic acid, distinguishing isolates with ESBLs from those that are resistant for other reasons.
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