Plasmid Mediated Genes And Mutation In Gyra Gene Confer Quinolone - Antibiotic Resistance In Enterobacteriaceae Independently

Background: Both plasmid mediated quinolone resistance (PMQR) genes and mutations within the quinolone resistance-determining regions (QRDRs) contribute in emergence of quinolone-resistant bacteria. Point mutations in gyrA gene has been reported to reduce susceptibility of bacteria to fluroquinolone antibiotics. This study was designed to assess these mechanisms of quinolone resistance to Enterobacteriaceae bacteria. Methods and materials: Enterobacteriaceae bacteria were isolated and identified from urinary tract infection (UTI) patients and from poultry feces. Phenotype antibiotic susceptibility was tested by Kirby Baur disc diffusion method using quinolone and fluoroquinolone antibiotics, such as lomefloxacin, ofloxacin, ciprofloxacin, and nalidixic acid. Polymerase chain reaction (PCR) was performed to detect plasmid mediated quinolone resistance (PMQR) genes including qnrA, qnrB, and qnrS. Mutations within the quinolone resistance-determining regions (QRDRs) of gyrA was examined in parallel. Sequencing of QRDRs gene, gyrA was subjected of 14 isolates from three groups: (1) phenotypic resistant plus carrying at least one PMQR gene, (2) phenotypic resistant without PMQR gene, (3) phenotypic sensitive without PMQR gene. As negative control ATCC 25922 strain, Escherichia coli was assessed. Results: A total of 140 bacteria (85 from UTI and 55 from poultry feces) was isolated which contained about 30% Proteus sp., 31.4% Klebsiella sp., 13.6% E. coli, 7.9% Salmonella sp., 10% Shigella sp., 6.4% Pseudomonas sp., and 0.7% Enterobacter sp. Phenotypic resistance was observed in 99.3%, 87.1%, 84.3% and 92.9% of the total isolates against lomefloxacin, ofloxacin, ciprofloxacin, and nalidixic acid, respectively. PMQR genes, qnrS, qnrA, and qnrB genes were found in 68.6%, 11.4%, and 2.9% isolates, respectively. Detection of qnrA, and qnrB overlapped 100% with qnrS, however, only 6% (1/16) co-harboring of qnrA was observed with qnrB. Two mutations (Ser-83 to Leu and Asp-87 to Asn) in gyrA were detected only in group-2 isolates belonging phenotypic resistant without PMQR gene. Isolates from two other groups did not show any mutation in their gyrA gene. Conclusion: Acquisition of the PMQR genes and mutation in the QRDR confer resistance in Enterobacteriaceae to quinolone antibiotics independently. gyrA mutations at Ser-83 and Asp-87 are critical with high levels of quinolone resistance in Enterobacteriaceae.