Characterization of blaCTX-M sequences of Indian origin and thirteen uropathogenic Escherichia coli isolates resistant to multiple antibiotics.

A cohort of 13 urinary isolates of E. coli (obtained from patients at the Sri Sathya Sai Institute of Higher Medical Sciences, Prasanthigram, Andhra Pradesh, India) were characterized and found to be resistant to multiple antibiotics, including extended-spectrum cephalosporins. All 13 isolates contained blaCTX-M-15, and many of them transferred this genotype to at least one laboratory strain of E. coli after conjugation. Analyses of blaCTX-M-15 sequences (n = 141) of Indian origin showed that > 85% of them were obtained from bacteria not associated with the urinary tract, and that E. coli isolates account for majority of all blaCTX-M-15-carrying bacteria reported from India. Other types of blaCTX-M appear to be rare in India, since only six such sequences were reported as of July 2015. The results indicate that 'selection pressure' exerted by extended-spectrum cephalosporins may have stabilized the blaCTX-M-15 genotype among E. coli in India. The rarity of other blaCTX-M suggests that they lack the survival advantage that blaCTX-M-15 may have.