Occurrence and detection of AmpC β-lactamases among Enterobacteriaceae isolates from patients at Ain Shams University Hospital
Background: AmpC β-lactamases are often plasmid mediated that hydrolyze all b-lactam antibiotics except cefepime and carbapenems.
Aim of the study: 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.
Subjects and methods: 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.
Results: 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.
Conclusion: 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.
KEYWORDS: AmpC β-lactamase; Enterobacteriaceae; Plasmid encoded; Phenotype; Genotype; Multiplex PCR