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Chapter 5.12 : Extended-Spectrum Beta-Lactamase Testing for Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis
Extended-Spectrum Beta-Lactamase Testing for Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis, Page 1 of 2< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555818814/9781555818814_Chap5.12-1.gif /docserver/preview/fulltext/10.1128/9781555818814/9781555818814_Chap5.12-2.gif
Extended-spectrum beta-lactamases (ESBLs) are enzymes that hydrolyze or inactivate extended-spectrum cephalosporins, aztreonam, and expanded-spectrum penicillins. ESBLs are derived from point mutations in the genes that encode common beta-lactamases such as TEM-1, TEM-2, or SHV-1, which confer resistance to penicillins but not to extended-spectrum cephalosporins. The mutations of these common beta-lactamases extend the spectrum of beta-lactam antimicrobial agents that are hydrolyzed to include those with an oxyimino side chain (such as cefotaxime, ceftriaxone, and ceftazidime). The oxyimino-monobactam aztreonam is also hydrolyzed by ESBLs. However, ESBL enzymes do not hydrolyze carbapenems and generally do not hydrolyze cephamycins (such as cefoxitin and cefotetan). ESBL activity is blocked by beta-lactamase inhibitors such as clavulanic acid, and laboratory tests for confirming ESBL-producing bacteria are based on this property. The phenotypic ESBL confirmatory test can be performed by disk diffusion or by a broth microdilution MIC method. Commercially available ESBL Etest strips may also be used for ESBL confirmatory testing (see “Procedure Notes” below).