Erythromycin resistance and virulence genes in Enterococcus faecalis from swine in China

This study aims to describe the erythromycin resistance phenotypes and genotypes, and the prevalence of virulence genes of Enterococcus faecalis isolated from swine in China. A total of 117 nonreplicate E. faecalis isolates, obtained from 502 clinical samples taken from different pig farms between 2007 and 2009 were included in the study Minimum inhibitory concentrations were determined using the broth microdilution method. All of the isolates were screened for the presence of seven virulence genes (ace, asa1, cylA, elaA, esp, gelE, and hyl). In addition, the DNA from erythromycin-resistant isolates were amplified with primers specific for erythromycin resistance erm (A), erm(B), erm(C), mef(A/E), and msr(C) genes. Results show that erythromycin, tylosin, and ciprofloxacin resistance rates in E. faecalis were 66.67% (n=78), 66.67% (n=78), and 64.10% (n=75), respectively. About 69.23% of isolates (n=81) were positive for gelE, 48.72% (n=57) for ace, 15.38% (n=18) for efa, 7.69% (n=9) for asa1, and 6.84% (n=8) for esp. Among the erythromycin-resistant isolates, erm(B) (n=54) was the most prevalent resistance gene, followed by erm(A) (n=37). A significant correlation was found between the presence of the gelE virulence gene and erythromycin resistance (P < 0.05). These findings suggest that enterococci from swine should be regarded with caution because they can be reservoirs for antimicrobial resistance and virulence genes.