Multiple Antimicrobial Resistance and Novel Point Mutation in Fluoroquinolone-Resistant Escherichia coli Isolates from Mangalore, India

Fluoroquinolone resistance in bacteria is usually associated with mutations in the topoisomerase regions. We report a novel point mutation in fluoroquinolone-resistant Escherichia coli strains. E. coli isolated from the environment in and around Mangalore, India, were examined for their antimicrobial resistance profile to 12 antibiotics and for the antibiotic resistance genes by polymerase chain reaction. Of the 67 E. coli isolated, 24 (35.8%) were sensitive to all antibiotics and 43 (64.2%) showed resistance to at least one of the 12 antibiotics used in the study. One isolate (EC10) was resistant to nine of the 12 antibiotics used. Resistance to nalidixic acid was the most common (34.32%), followed by nitrofurantoin (26.86%), tetracycline (22.38%), ampicillin (20.89%), cotrimoxazole (13.43%), ciprofloxacin (11.94%), gentamicin (10.44%), piperacillin/tazobactam (7.46%), chloramphenicol (7.46%), and cefotaxime (4.47%). Least resistance was observed for meropenem (1.49%) and none of the isolates showed resistance to imipenem. All the isolates harbored resistance genes corresponding to their antimicrobial resistance. Few quinolone-resistant isolates carried single point mutation (ser83Leu) and some had double point mutation (Ser83Leu and Asp87Asn) in gyrA. A third novel point mutation was also observed at position 50 with the change in the amino acid from tyrosine to cysteine (Tyr50Cys) in gyrA region. The study throws light on a novel point mutation in fluoroquinolone-resistant isolates. While the study helps to understand the risk and occurrence of antibiotic resistance among gram-negative bacteria from the environment, the alarming rate of antibiotic-resistant bacteria is a cause of concern in addressing infections.