PHENOTYPIC AND MOLECULARCHARACTERIZATION OF PLASMID -MEDIATED AMPC ?-LACTAMASES AMONG GRAMNEGATIVE CLINICAL ISOLATES.

There are currently no standardized phenotypic methods for the screening and detection of plasmid -mediated AmpC enzymes. Aim: to evaluate two phenotypic methods (AmpC E test and cefoxitin –cloxacillin double disc synergy) to detect AmpC enzymes in Escherichia coli, Klebsiella spp., and Proteus mirabilis using multiplex PCR as gold standard method. Materials and methods: total of 1500 gram negative isolates were screened for potential plasmid-mediated AmpC enzymes by Cefoxitindisc.AmpC E test and cefoxitin –cloxacillin double disc synergy tests were used to confirm detection of plasmid-mediated AmpC enzymes.The genotypic identification was done using multiplex PCR. Results:The potential Amp C-producing isolates among all the studied isolates were only 4.7 % (70/1500) by cefoxitin disc. Among the cefoxitin resistant isolates,22.9 % and 24.3 % confirmed to be P-AmpC by cefoxitin-cloxacillin double disc synergy test and AmpC-Etest, respectively. Plasmid encoded AmpC genes were detected by PCR in 27% of cefoxitin resistant isolates. The most prevalent AmpC gene family was CIT and MOX.The sensitivity of AmpC E test and cefoxitin –cloxacillin double disc synergy were 81.3 % and100 % respectively and the specificity were 92.3% and 95.9%.