Molecular characterization of antimicrobial resistance in enterococcus faecalis and enterococcus faecium isolated from pigs and pork in Thai-Laos border area

A total of 365 Enterococcus faecalis (n=78) and Enterococcus faecium (n=287) confirmed by multiplex PCR were originated from 472 pig and pork samples in Thai-Lao border area. All PCR confirmed E. faecalis and E. faecium were determined for antimicrobial resistance phenotype, genotype and virulence genes. Eighty one isolates of E. faecalis (n=30) and E. faecium (n=51) were randomly selected and tested for their plasmid profile. E. faecalis and E. faecium were resistant to ampicillin (4% and 22%), chloramphenicol (36% and 12%), erythromycin (75% and 48%), gentamicin (59% and 7%), streptomycin (73% and 37%) and tetracycline (86% and 62%), respectively. The most frequent resistance pattern was ERY-GEN-STR-TET in E. faecalis (28.2%) and TET in E. faecium (13.6%). The tetM gene (82% and 56%) was the most common in both enterococci followed by tetL (64% and 46%). Antimicrobial resistance genes were more common in E. faecalis than E. faecium except ermA (P<0.05). All of the int positive isolates (1.3% E. faecalis and 5.2% E. faecium) carried empty class 1 integrons without gene cassettes. The agg, cylA, gel and esp genes were found in E. faecalis while gel gene only was detected in E. faecium from Thailand (33%). Antimicrobial resistance phenotype was associated with antimicrobial resistance and virulence genes in E. faecalis while it was only associated with antimicrobial resistance genes in E. faecium. Most of the enterococci carried one to four plasmids with a molecular weight of 0.03-35 kb in E. faecium (96%) and 19-34 kb in E. faecalis (100%). The results showed that E. faecalis and E. faecium may serve as a reservoir for spread of AMR and virulence determinants in pigs, pork and humans.