Prevalence and characteristics of extended-spectrum β-lactamase genes in Escherichia coli isolated from piglets with post-weaning diarrhea in Heilongjiang province, China

Objectives: The purpose of this study was to investigate the prevalence of extended spectrum β-lactamase (ESBL) genes in Escherichia coli isolated from post-weaning diarrhea (PWD) piglets in Heilongjiang province, China. Methods: Of 458 E. coli isolated from 589 fecal samples from PWD piglets, a total of 198 isolates were confirmed as ESBL producers by the double-disk synergy test (DDST). Polymerase chain reaction (PCR) and sequencing were performed to identify genes for ESBL, plasmid-mediated quinolone resistance (PMQR), and integrons. Results: Of the 198 isolates, bla(CTX−M) and bla(TEM) were detected in 191 and 149 isolates, respectively. Sequencing revealed that 10 bla(CTX−M) subtypes were detected, and bla(CTX−M−14) was the most prevalent, followed by bla(CTX−M−55) and bla(CTX−M−65). Of the 149 TEM-positive strains, four were bla(TEM−52) and the rest were bla(TEM−1). Among the 198 ESBL-positive isolates, 173 isolates were found to harbor at least one PMQR gene, with oqxAB, qnrS, qnrB, qepA, and aac(6′)-Ib-cr being detected alone or in combination in 125, 114, 26, 24, and 45 strains, respectively. One hundred and fifty-five ESBL-positive isolates were also positive for class I integron (int1), and eight different gene cassette arrays were confirmed in 110 isolates by restriction fragment length polymorphism (RFLP) and DNA sequencing analyses, with predominance of dfrA17-aadA5, dfrA12-orfF-aadA2, and dfrA1-aadA1 arrays. Conclusion: To the best of our knowledge, this is the first report of the bla(TEM−52) gene in pig E. coli isolates in China and this is also the first description of the coexistence of the qnrB, qnrS, aac(6′)-Ib-cr, qepA, and oqxAB genes in one E. coli strain.