Prevalence Escherichia coli, Klebsiella and Enterobacter Species and AmpC-producing Enterobacteriaceae in Clinical Specimens of Hospitals Affiliated to Babol University of Medical Sciences, Iran using Phenotypic and Molecular Methods

 AmpC-producing bacteria are a severe threat to treating infectious diseases caused by gram-negative bacteria. The actual prevalence of these bacteria is not clearly determined as there is no reliable diagnostic method available to detect them. Therefore, this study was performed to determine the frequency of Escherichia coli, Klebsiella, and Enterobacter species producing AmpC among clinical samples by phenotypic and molecular methods.

 In this study, 163 bacteria of Enterobacteriaceae species isolated from different clinical samples in 2018 were examined. Suspected isolates of producing pAmpC were identified using cefoxitin disk (FOX) and disk diffusion method. Three confirmatory phenotypic methods were performed to identify pAmpC production, and blaDHA, blaFOX, blaMOX genes were searched using a molecular method for all bacteria. Specificity and sensitivity of phenotypic tests were obtained compared to the presence of blaDHAgene.

Of 163 bacteria, 80 (49.1%) isolates were resistant to FOX, and 21 (12.9%) carried the blaDHA gene. Among the bacteria carrying the gene, 5 (6%) isolates were sensitive to FOX. 49 (61.3%) FOX-resistance bacteria were positive in one of the chromosomal and/or plasmid phenotypic tests. The highest specificity and sensitivity were observed in the AmpC disk (90.8%) and CAM (42.7%) methods, respectively.

It seems phenotypic methods are more successful in distinguishing true negatives (higher specificity). Also, sensitivity to cefoxitin is not a criterion for not producing the enzyme AmpC. For this reason, it is recommended that national monitoring be performed to identify the genes of AmpC producing bacteria.