Molecular Characterization of Multidrug-Resistant Escherichia coli Isolates from Edible Offal in Korea

Edible offal, which is the nonmuscular part of the livestock, is a popular food product in many countries. However, it can be easily contaminated by bacteria, such as Escherichia coli, during slaughter and processing and regarded as a reservoir for transfer of antimicrobial-resistant bacteria to humans. This study aimed to investigate prevalence and characteristics of antimicrobial-resistant E. coli isolates from edible offal in Korea. A total of 320 chicken offal samples, 540 pig offal samples, and 560 cattle offal samples were collected. Among the 118 E. coli isolates obtained, resistance to at least one antimicrobial agent was revealed in 32 (100%), 46 (95.8%), and 26 (68.4%) isolates of chicken, pig, and cattle offals, respectively, with an overall prevalence of 88.1% (104 of 118). The isolates from chicken offal showed highest resistance to most antimicrobial agents, with the exception of higher ampicillin resistance for isolates from pig offal. In the distribution of antimicrobial resistance genes of 69 (58.5%) multidrug-resistant (MDR) E. coli, bla(TEM-1) (97.1%), tetA (76.6%), sul2 (70.6%), and cmlA (57.4%) were most prevalent. Class 1 and class 2 integrons were detected in 82.6 and 2.9% of the MDR isolates, respectively. In total, seven virulence genes (eaeA, escV, astA, fimH, papC, sfa/focDE, and iucC) were also identified in the MDR isolates. The fimH gene was the most frequent (91.3%). Overall, 52 isolates from chicken (24 isolates, 96.0%), pig (16 isolates, 55.2%) and cattle (12 isolates, 80.0%) offals among MDR isolates were found to have some plasmid replicons. Frep (38 isolates) and FIB (27 isolates) replicons were more prevalent than other replicon types. The results suggest that edible offal can become a relevant reservoir of E. coli strains carrying various antimicrobial resistance and virulence genes.