Occurrence and detection of AmpC β-lactamases among Enterobacteriaceae isolates from patients at Ain Shams University Hospital

AmpC β-lactamases are often plasmid mediated that hydrolyze all β-lactam antibiotics except cefepime and carbapenems. We aimed to evaluate the presence of AmpC β-lactamase among Enterobacteriaceae isolates separated from patients with nosocomial infections, and to detect the genetic basis for AmpC production in these strains. 50 AmpC β-lactamase Enterobacteriaceae were analyzed for the presence of AmpC production. Three phenotypic AmpC confirmation assays (AmpC E test, the disk approximation test, Amp C EDTA disc) were able to detect the majority of AmpC-positive strains correctly. Molecular detection of plasmid mediated AmpC by multiplex PCR was conducted on them. The results show that from the 148 total isolates obtained from ICU admitted patients with suspected nosocomial infections, 50 (33.8%) were AmpC β-lactamase isolates. For the 50 AmpC isolates, all phenotypic Amp C tests gave a positive result. Among these isolates, plasmid encoded AmpC genes were detected by multiplex PCR in 46 (92%) isolates, which included Klebsiella pneumoniae (n = 22) (47.8%), Escherichia coli (n = 15) (32.6%), and Proteus mirabilis (n = 9) (19.6%). One E. coli, one K. pneumoniae, and two P. mirabilis isolates showed no AmpC gene. The most prevalent AmpC gene was that belonging to family CMY-1 which was detected in 73.9% (34/46) of all isolates. It could be concluded that: Amp C producing isolates among Enterobacteriaceae strains have been increasingly recognized in the Ain Shams University Hospital. Thus, molecular identification of the genes encoding AmpC would be essential for a reliable epidemiological investigation of their transmission in hospitals.