involvement of mutation in the serine 83 of quinolone resistant determining regions of the GyrA Gene in resistance to ciprofloxacin in Escherichia coli

Appearance of bacteria resistant to antibacterial agents puts physicians in trouble and threatens the health of the world. The rapid development of bacterial resistance in Escherichia coli to ciprofloxacin makes difficult the treatment of infectious diseases. So, detection of the locations of possible mutations in gyrase A gene ( gyrA ) in these mutants is very important to determine the mechanism of this resistance. In the present study, ciprofloxacin-resistant mutants were isolated from medium containing ciprofloxacin. Polymerase chain reaction (PCR) was used to amplify the gyrA gene in these mutants and DNA sequencing was used to determine the location of mutation in this gene. Results showed that the most of ciprofloxacin-resistant mutants contain mutations in quinolone resistance- determining region (QRDR) of A subunit of DNA gyrase and specially at serine 83. However, mutations outside of this region were also found at tyrosine 50 and alanine 119. In conclusion, this study confirms that mutation in serine 83 of QRDR in A subunit of DNA gyrase is the main cause of resistance to ciprofloxacin in E. coli.