Investigation of plasmid mediated AmpC beta-lactamases in Escherichia coli and Klebsiella pneumoniae isolates by phenotypic and genotypic

Objective: To investigate the susceptibility and specificity of the phenotypic methods to determine plasmid-mediated AmpC. Methods: The cross-sectional study was conducted at Duzce University Faculty of Medicine, Microbiology Laboratory from January 2015 to June 2016, and comprised Escherichia coli and Klebsiella pneumonia isolates intermediate susceptible or resistant to cefoxitine. Combined disk diffusion test, double disc synergy test, agar gradient test and polymerase chain reaction were used to detect plasmid-mediated AmpC. Results: Of the 2024 E. coli samples, 44(2.17%), and of the 792 K. pneumoniae samples, 16(2%) were included. Combined disk diffusion test had susceptibility of 68% and specificity of 50%; double disc synergy test 24% and 82%; and agar gradient test 40% and 68%. Of the isolates positively detected by polymerase chain reaction method, more than one gene region positivity was detected in 15(25%) isolates. Conclusion: All three phenotypic methods were found to be insufficient to detect plasmid-mediated AmpC positivity.