Abstract The aim of this study was to examine mutations in the quinolone-resistance-determining region (QRDR) of gyrA and parC genes in Pseudomonas aeruginosa isolates. A total of 100 clinical P. aeruginosa isolates were collected from different university-affiliated hospitals in Tabriz, Iran. Minimum inhibitory concentrations (MICs) of ciprofloxacin and levofloxacin were evaluated by agar dilution assay. DNA sequences of the QRDR of gyrA and parC were determined by the dideoxy chain termination method. Of the total 100 isolates, 64 were resistant to ciprofloxacin. No amino acid alterations were detected in gyrA or parC genes of the ciprofloxacin susceptible or ciprofloxacin intermediate isolates. Thr-83 → Ile substitution in gyrA was found in all 64 ciprofloxacin resistant isolates. Forty-four (68.75%) of them had additional substitution in parC. A correlation was found between the number of the amino acid alterations in the QRDR of gyrA and parC and the level of ciprofloxacin and levofloxacin resistance of the P. aeruginosa isolates. Ala-88 → Pro alteration in parC was generally found in high level ciprofloxacin resistant isolates, which were suggested to be responsible for fluoroquinolone resistance. These findings showed that in P. aeruginosa, gyrA was the primary target for fluoroquinolone and additional mutation in parC led to highly resistant isolates.

Transference of resistance determinants by integrons is one of the important factors that can contribute to the increase in multi-resistant bacteria. We determined the prevalence and class of integrons among multi-drug resistant (MDR) Escherichia coli strains isolated from clinical specimens in Tabriz teaching hospitals. Firstly, susceptibility of 140 isolates to 13 antibiotics was determined using the disc diffusion method. Then, prevalence and class of integrons was detected in MDR strains by PCR-RFLP. One hundred five (75%) of total 140 isolates were uropathogenic Escherichia coli (UPEC). Other pathotypes included were: diarrheagenic Escherichia coli (13; 9.3%), sepsis-associated E. coli (5; 3.6%) and newborn meningitis-associated E. coli (2; 1.4%). Antibiotic resistance patterns were as follows: amoxicillin 99.3%, gentamicin 33.6%, tetracycline 72.8%, ceftazidime 46.4%, co-trimoxazole 75%, imipenem 1.4%, ciprofloxacin 47.6%, norfloxacin 50.7%, cephalothin 77.8%, amikacin 12.1%, nitrofurantoin 12.9%, chloramphenicol 20.7% and nalidixic acid 60.7%. One hundred eighteen (84.2%) of tested isolates were multi-drug resistant. Prevalence of integrons was confirmed in 27.1% of MDR isolates. intI1 and intI2 were detected respectively in 22.05% and 5.08% of MDR strains. No intI3 was detected. Resistance to gentamicin, amikacin and chloramphenicol was significantly associated with the presence of integrons. These results showed high resistance of E. coli to routine antibiotics, however, in consideration of low prevalence of integrons among these strains, we can conclude that antibiotic resistance genes in these strains presumably carried on elements other than integrons.