Background and Objectives: AmpC beta-lactamases are among cephalosporinases encoded on the chromosomes of many Enterobacteriaceae. In many bacteria, induction of AmpC enzymes can be made at a very high level by numerous mutations. In this study, the prevalence of chromosomal AmpC genes, was investigated in the isolates of Pseudomonas aeruginosa isolated from teaching hospitals in Zahedan city in 2015.

Methods: In this descriptive cross-sectional study, 100 P. aeruginosa isolates were isolated from 391 clinical samples using biochemical and conventional methods. cefoxitin (30μg) disk diffusion method was used to isolate AmpC-producing strains, and multiplex PCR was used to identify chromosomal AmpC genes. ESBL containing strains was assessed using ceftazidime (30μg) and cefotaxime/clavulanic acid (30μg/10μg) disk diffusion tests. Data analysis was performed using χ² test.

Results: In primary phenotypic screening, out of 100 P. aeruginosa isolated, 88 isolates were ESBL producers and 20 isolates (20%) were AmpC beta-lactamase producers. Among 20 phenotypically identified AmpC producing isolates, 19 isolates (95%) had FOX gene, 7 isolates (35%) had EBC gene, 4 isolates (20%) had ACC gene, and 15 isolates isolates (75%) had DHA gene, which were detected by multiPlex PCR assay.

Conclusion: The results of the present study indicated that the presence of AmpC leads to resistance of bacteria to many cephalosporins. Also, use of multiplex PCR yields the best results in the group identification of these genes.