Occurrence and molecular characteristics of antimicrobial resistance of Escherichia coli from broilers, pigs and meat products in Thailand and Cambodia provinces

Nine hundred and forty-one samples were collected in Sa Keao, Thailand (n=554) and Banteay Meanchey, Cambodia (n=387) from July 2014 to January 2015. A total of 667 Escherichia coli isolates (381 isolates from Sa Keao and 286 isolates from Banteay Meanchey) were obtained and examined for antimicrobial susceptibility, class 1 integrons, ESBL genes and horizontal transfer of resistance determinants. Prevalence of E. coli in pig and broiler carcass samples from slaughterhouses and fresh markets was 36-85% in Sa Keao and 11-69% in Banteay Meanchey. The majority of these isolates were multidrug resistant (75.3%). Class 1 integrons were common in both Thai (47%) and Cambodian (62%) isolates, of which four resistance gene cassette arrays including aadA1, dfrA1-aadA1, dfrA12-aadA2 and aadA2-linF were identified. Class 1 integrons in two broiler isolates from Sa Keao (dfrA12-aadA2) and one broiler isolate from Banteay Meanchey (dfrA1-aadA1) were horizontally transferable. Sixteen isolates were confirmed to be ESBL-producing strains with ESBL gene bla(CTX-M-15), broad spectrum -lactamase gene bla(TEM-1) and the AmpC gene bla(CMY-2) being detected. The bla(TEM-1) gene was most prevalent and located on a conjugative plasmid.