High Prevalence of Ciprofloxacin Resistance in Community Associated Staphylococcus aureus in a Tertiary Care Indian Hospital

We have studied the nature of ciprofloxacin resistance in methicillin sensitive and resistant Staphylococcus aureus among patients in a tertiary care hospital in Bengaluru, South India. All the isolates were highly resistant to ciprofloxacin. Molecular characterization of these samples performed using Staphylococcal Cassette Chromosome typing and multilocus sequence typing showed that 37.5% of total isolates and 59% of MRSA were sequence type (ST)772 and the rest were other STs. This indicates high prevalence of CA-MRSA in this tertiary care hospital serving the Indian community. Mutations responsible for ciprofloxacin resistance among these isolates in DNA gyrase (gyrA and gyrB) and topoisomerase IV (grlA and grlB) were analyzed by PCR amplification of specific fragments and sequencing. We found that for ST772 and five other STs present in this collection, single mutation in the gyrA gene, Ser-84→Leu, was sufficient for the high resistance. In vitro generation of ciprofloxacin resistance in two sensitive ST772 isolates by exposure to increasing antibiotic concentrations also resulted in the same single mutation of gyrA. The factors responsible for high ciprofloxacin resistance are varied and are dependent on the genetic background of the isolates and the environment. This is the first report on the mechanism of ciprofloxacin resistance among the most prevalent Indian CA-MRSA.