The performance of a resazurin chromogenic agar plate with a combined disc method for rapid screening of extended‐spectrum‐β‐lactamases, AmpC β‐lactamases and co‐β‐lactamases in Enterobacteriaceae

ABSTRACTA promising means of rapid screening of extended‐spectrum‐β‐lactamase (ESBL), AmpC β‐lactamase, and co‐production of ESBL and AmpC that combines resazurin chromogenic agar (RCA) with a combined disc method is here reported. Cefpodoxime (CPD) discs with and without clavulanic acid (CA), cloxacillin (CX) and CA+CX were evaluated against 86 molecularly confirmed β‐lactamase‐producing Enterobacteriaceae, including 15 ESBLs, 32 AmpCs, nine co‐producers of ESBL and AmpC and 30 carbapenemase producers. The CA and CX synergy test successfully detected all ESBL producers (100% sensitivity and 98.6% specificity) and all AmpC producers (100% sensitivity and 96.36% specificity). This assay also performed well in screening for co‐existence of ESBL and AmpC (88.89% sensitivity and 100% specificity). The RCA assay is simple and inexpensive and provides results within 7 hr. It can be performed in any microbiological laboratory, in particular, in geographic regions in which ESBL, AmpC or co‐β‐lactamase‐producing Enterobacteriaceae are endemic.