Evaluation of a chromogenic agar medium for the detection of extended-spectrum ß-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 ß-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 ß-lactamases (pAmpCBLs) were characterized by PCR and sequencing. Among the 256 specimens, 17 (6.6%) ESBL producers were isolated on both media. The sensitivity, specificity, positive predictive value and negative predictive value were higher for KC-ESBL (100, 93.3, 51.5 and 100%, respectively) than for SB-ESBL (88.2, 92.9, 46.9 and 99.1%, respectively) (P = 0.72). 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.