Comparison between Multiplex PCR and Phenotypic Detection Methods for Identifying AmpC B-lactamases Among Clinical Isolates of Enterobacteriaceae in Zagazig University Hospitals, Egypt

No standardized phenotypic methods for the screening and detection of plasmid-mediated AmpC enzymes are currently available, which is one of the main problems we are facing nowadays.

Aim: This study aimed to evaluate the presence of AmpC β-lactamase among Enterobacteriaceae isolates separated from patients with nosocomial infections and to detect the most prevalent genetic strains in the separated isolates and evaluation of two phenotypic methods (AmpC E test and cefoxitin–cloxacillin double disc synergy test) to detect AmpC enzymes.

Materials and methods: Total of 1200 gm negative isolates were screened for potential plasmid-mediated AmpC enzymes by cefoxitin disc, AmpC E test and cefoxitin–cloxacillin double disc synergy tests. The genotypic identification was done using multiplex PCR.

Results: The potential AmpC producing isolates among all the studied isolates were 4.1% (49/1200) by cefoxitin disc. Plasmid encoded AmpC genes were detected by PCR in 28.5% of cefoxitin resistant isolates. The most prevalent AmpC genes family were CIT and MOX. The sensitivity of AmpC E test and cefoxitin–cloxacillin double disc synergy were 81.3% and 100% respectively and the specificity were 92.3% and 95.9%.