Evaluation of a chromogenic agar medium for the detection of extended-spectrum β-lactamase-producing Enterobacteriaceae

Aim: To compare the performance of a new chromogenic agar medium CHROMagar ESBL (KC-ESBL) to chromID ESBL (SB-ESBL) for the detection and presumptive identification of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae directly from clinical specimens. Methods and Results: A total of 256 specimens were screened for ESBL producers. Also, the genotypes of the ESBLs and plasmid-mediated AmpC beta-lactamases (pAmpCBLs) were characterized by PCR and sequencing. Among the 256 specimens, 17 (6 center dot 6%) ESBL producers were isolated on both media. The sensitivity, specificity, positive predictive value and negative predictive value were higher for KC-ESBL (100, 93 center dot 3, 51 center dot 5 and 100%, respectively) than for SB-ESBL (88 center dot 2, 92 center dot 9, 46 center dot 9 and 99 center dot 1%, respectively) (P = 0 center dot 72). Enterobacteriaceae harbouring pAmpCBL genes as well as chromosomal cephalosporinase- and penicillinase-hyperproducing Enterobacteriaceae and Pseudomonas aeruginosa accounted for the false-positive results. Conclusion: KC-ESBL can detect ESBL producers from clinical specimens with good selectivity and rapid presumptive identification by means of colony colour at 24 h. Significance and Impact of the Study: This is the first study that has evaluated the performance of KC-ESBL that enables the detection and presumptive identification of ESBL producers from clinical specimens.