Diverse Genetic Array of blaCTXM-15 in Escherichia coli: A Single-Center Study from India.

CTX-M-15 is a chief contributor for expanded-spectrum cephalosporin and monobactam resistance in India, complicating treatment options. In this study, we have investigated genetic context of CTX-M-15 in Escherichia coli and their transmission dynamics in a tertiary referral hospital of India. A total of 198 isolates were collected, of which 66 were harboring blaCTXM-15. Among them, 14 isolates were carrying a single CTX-M-15 gene and 52 were harboring multiple extended-spectrum β-lactamase genes along with blaCTX-M-15. The resistance gene was flanked by tnpA, ISEcp1, IS26, and ORF477 in 10 different arrangements. The resistance determinant was horizontally transferable through F, W, I1, and P Inc types of plasmids. Restriction mapping of plasmids showed a variable band pattern even within the same Inc types. Minimum inhibitory concentration was found above the breakpoint level against expanded-spectrum cephalosporins and monobactam while susceptible against carbapenems. blaCTX-M-15 was highly stable and sustained in the cell after 115 serial passages. In pulse-field gel electrophoresis, eight pulsotypes of E. coli were found to be responsible for the spread of blaCTX-M-15 in the tertiary referral center. We conclude that the presence of CTX-M-15 in the heterogeneous group of E. coli is highly alarming in terms of infection control and it may require regular monitoring, so as to formulate appropriate antibiotic policy to stop the spread of this resistance determinant.