title: Genetic characterization of fluoroquinolone-resistant Escherichia coli associated with bovine mastitis in India.
abstract: OBJECTIVE
  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.
  
  
  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 83(rd) and 87(th) amino acid position of gyrA gene, and at 80(th) and 108(th) amino acid position of parC gene 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: S83⟶L and D87⟶N; at parC: S80⟶I) and the fifth isolate showed an additional mutation at codon 108 of parC (A108⟶T) with the increased ciprofloxacin MIC of 16-128 µg/ml. The most common mutation noticed were at S83⟶L and D87⟶N of gyrA and S80⟶I of ParC.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Veterinary Microbiology, Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry - 605 009, India.
authors.forename: Sangeetha
authors.initials: S
authors.lastname: Balakrishnan
authors.affiliation: Department of Veterinary Microbiology, Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry - 605 009, India.
authors.forename: Prabhakar Xavier
authors.initials: PX
authors.lastname: Antony
authors.affiliation: Department of Veterinary Microbiology, Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry - 605 009, India.
authors.forename: Hirak Kumar
authors.initials: HK
authors.lastname: Mukhopadhyay
authors.affiliation: Department of Veterinary Microbiology, Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry - 605 009, India.
authors.forename: Raghavan Madhusoodanan
authors.initials: RM
authors.lastname: Pillai
authors.affiliation: Department of Veterinary Biochemistry, Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry - 605 009, India.
authors.forename: Jacob
authors.initials: J
authors.lastname: Thanislass
authors.affiliation: Department of Veterinary Medicine, Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry - 605 009, India.
authors.forename: Vijayalakshmi
authors.initials: V
authors.lastname: Padmanaban
authors.affiliation: Department of Veterinary Microbiology, Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry - 605 009, India.
authors.forename: Mouttou Vivek
authors.initials: MV
authors.lastname: Srinivas
keywords: Escherichia coli; fluoroquinolones; gyrA; parC; quinolone resistance determining region