Prevalence of blaCTX-M and Emergence of blaCTX-M-5-Carrying Escherichia coli in Chrysomya megacephala (Diptera: Calliphoridae), Northern Thailand.

This study was undertaken to assess the prevalence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (ESBL-EC) among blow fly (Chrysomya megacephala) populations in Northern Thailand. Of 600 blow flies collected from rural (n = 400) and urban (n = 200) areas, 334 blow flies carried ESBL-EC (55.7%). Prevalence of ESBL-EC in blow flies captured from rural areas was significantly higher than that from urban region (72.5% vs. 22.0%, p < 0.001). Susceptibility tests revealed that 68.6% of ESBL-EC possessed multidrug-resistant phenotypes. Coresistance to gentamicin (85%) was common, while resistance to ciprofloxacin was relatively low (18.0%). Of the 334 isolates, 253 isolates (75.7%) harbored blaCTX-M, in which blaCTX-M group 1 was predominant (56.5%), followed by blaCTX-M group 9 (39.1%). Interestingly, a single isolate was found to carry blaCTX-M-5, which resided on the IncA/C conjugative plasmid. This is the first report of blaCTX-M-5 from Thailand and its first identification in blow fly. Pulsed field gel electrophoresis (PFGE) demonstrated high genetic diversity among ESBL-EC isolates. Nevertheless, identical and closely related PFGE profiles were detected among isolates within the same regions and the regions which are several kilometers apart, suggesting that clonal transmission has occurred. Moreover, epidemiologically related isolates were observed between ESBL-EC from blow flies and human intestinal tract. This study provides evidences that blow flies, C. megacephala, are important reservoirs for ESBL-EC and could potentially act as vectors for the spread of ESBL-EC in a Thai community.