Effect of the Different Plasmid-Mediated AmpC Beta-Lactamase Genotypes on the Phenotypic Detection of ESBL in Enterobacteriaceae Isolates.

Background: Increasingly, Enterobacteriaceae isolates that are positive for the extended-spectrum-beta-lactamase (ESBL) by phenotypic screening tests yield a negative result when tested with the reference Clinical and Laboratory Standards Institute (CLSI) ESBL confirmatory test. The aim is to determine to what extent the different plasmid AmpC (pAmpC) genotypes could affect the CLSI ESBL confirmatory test for detection of the ESBL phenotype in ESBL/pAmpC co-producers.

Methods: A total of 253 Enterobacteriaceae isolates were screened for ESBL and AmpC production according to CLSI guidelines.