High prevalence of CTX-M belonging to ST410 and ST889 among ESBL producing E. coli isolates from waterfowl birds in China's tropical island, Hainan.

The epidemiology and genetic characteristics of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (E. coli) have been widely studied in human and veterinary settings. ESBL-producing E. coli are generally reported in pigs, poultry, and dairy farm animals. Here, we report on the prevalence and genetic characteristics of beta-lactamase producing E. coli isolated from waterfowl birds in Hainan, China. After phenotypic confirmation, genes encoding blaCTX-M, blaSHV and blaTEM were detected by polymerase chain reaction (PCR). The isolates were assigned to different phylogenetic groups, and multi-locus sequence typing (MLST). Taken as a whole, 289 (92.9%) out of 311 E. coli isolates from waterfowl birds were confirmed as ESBL phenotypes by double-disk synergy testing. Subsequent PCR analysis revealed that blaCTX-M was the predominant ESBL gene identified in 146 (46.9%) isolates, followed by the combination of blaCTX-M and blaTEM in 70 (22.5%) isolates. The majority of these positive isolates were assigned to phylogroup B2 (46.2%) followed by phylogroup A (43.6%). In addition, MLST assigned representative ESBL positive isolates (n = 40) to 18 STs, and ST410 (ST23cplx) was the most prevalent population (22.5%). The high prevalence of CTX-M and STs frequently associating with E. coli infections should be of concern as it poses threats to animal and public health. To the best of our knowledge, this is the first comprehensive study to report on the occurrence of ESBL producing E. coli from waterfowl birds in China.