Research (Published online: 11-07-2016)
5. Genetic characterization of fluoroquinolone-resistant Escherichia coli associated with bovine mastitis in India - Sangeetha Balakrishnan, Prabhakar Xavier Antony, Hirak Kumar Mukhopadhyay, Raghavan Madhusoodanan Pillai, Jacob Thanislass, Vijayalakshmi Padmanaban and Mouttou Vivek Srinivas
Veterinary World, 9(7): 705-709
doi: 10.14202/vetworld.2016.705-709
Aim: The present study was undertaken to characterize the mutation in gyrA (DNA gyrase) and parC (topoisomerase IV) genes responsible for fluoroquinolone resistance in Escherichia coli isolates associated with the bovine mastitis.
Materials and Methods: A total of 92 milk samples from bovine mastitis cases were sampled in and around Puducherry (Southern India). Among these samples, 30 isolates were bacteriologically characterized as E. coli. Minimum inhibitory concentrations (MIC) of fluoroquinolones of these 30 E. coli isolates were evaluated by resazurin microtiter assay. Then, the quinolone resistance determining region (QRDR) (gyrA and parC genes) of these E. coli isolates was genetically analyzed for determining the chromosomal mutation causing fluoroquinolone resistance.
Results: E. coli isolates showed a resistance rate of 63.33%, 23.33% and 30.03% to nalidixic acid, ciprofloxacin and enrofloxacin, respectively. Mutations were found at 83rd and 87th amino acid position of gyrA gene, and at 80th and 108th amino acid position of parCgene in our study isolates. Among these five isolates, one had a single mutation at 83 amino acid position of gyrA with reduced susceptibility (0.5 μg/ml) to ciprofloxacin. Then, in remaining four isolates, three isolates showed triple mutation (at gyrA: S83gL and D87gN; at parC: S80gI) and the fifth isolate showed an additional mutation at codon 108 of parC (A108gT) with the increased ciprofloxacin MIC of 16-128 μg/ml. The most common mutation noticed were at S83gL and D87gN of gyrA and S80gI of ParC.
Conclusion: The study confirms the presence of mutation/s responsible for fluoroquinolone resistance in QRDR of gyrA and parC genes of E. coli isolates of animal origin, and there is increased rate of fluoroquinolone resistance with high-level of MIC. The mutations observed in this study were similar to that of human isolates.
Keywords: Escherichia coli, fluoroquinolones, gyrA, parC, quinolone resistance determining region.
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