Horizontal transfer of between probiotic and in fermented soybean meal and in digestive tract of growing pigs.

BACKGROUND

The aim of this study was to investigate the intergeneric transfer of vancomycin resistance gene between probiotic enterococci in the fermentation progress of soybean meal and in the digestive tract of growing pigs. One genotype vancomycin resistant strain, E4, and one chloramphenicol-resistant strain, E2, were isolated from twenty-nine probiotic basis feed material / additive samples. For conjugation, E4 and E2 were used as starter to ferment soybean meal. For conjugation, thirty growing pigs were randomly assigned to five groups ( = 6), treated with a basic diet, or supplemented with 10% fermented soybean meal, 1% E4, 5% E2 or a combination of 1% E4 + 5% E2 for 7 d, respectively. Fecal samples of pigs in each group were collected daily for the isolation and dynamic analysis of E4, E2 and transconjugants. The sequence types (STs) of E4, E2 and transconjugants were analyzed by multilocus sequence typing (MLST). The harboring plasmid in E4 and transconjugants was analyzed by S1-pulsed field gel electrophoresis (PFGE) and further verified by multiple alignments.

RESULTS

The results showed that, in FSBM, transconjugants were detected 1 h after the fermentation, with a conjugation frequency of ~ 10 transconjugants / recipient. Transconjugants proliferated with E4 and E2 in the first 8 h and maintained steadily for 10 d till the end of the experiment. Additionally, experiment showed that transcojugants were recovered in one of six pigs in both FSBM and E4 + E2 groups, with conjugation frequency of ~ 10 and ~ 10, respectively. MLST revealed the ST of E4, E2 and transconjugants was ST1014, ST69 and ST69, respectively. S1-PFGE confirmed the existence of the -harboring, 142,988-bp plasmid, which was also a multi-drug resistant plasmid containing -like transposon.

CONCLUSIONS

The findings revealed the potential safety hazard existing in the commercial probiotic enterococci in China, because the horizontal transfer from farm to fork could potentially pose a safety risk to the public.