Tracing enterococci persistence along a pork production chain from feed to food in China

The prevalence and transmission of vancomycin-resistant Enterococcus (VRE) in enterococci being as probiotics has been neglected in the scientific literature. The application of enterococci in feed, food and health products may cause VRE transmission through the food chain. This study evaluated phenotypic resistance of Enterococcus species to 20 antibiotics along a pork production chain from feed to food. It also assessed the genetic diversity of Enterococcus faecium isolates. A total of 510 samples (feed, n = 70; swine manure, n = 400; swine carcasses, n = 20, and retail pork, n = 20) were collected in Beijing, China. A total of 328 enterococci isolates with 275 E. faecium and 53 Enterococcus faecalis were identified using 16 S rRNA. Antimicrobial susceptibility to all enterococci isolates was conducted using the K–B method for 20 antibiotics from 9 categories. Multilocus sequence typing (MLST) was conducted on the E. faecium isolates to survey the dissemination of enterococci in the pig industry. The results showed that only 26 enterococci isolates were sensitive to the 20 antibiotics, while half of the isolates (164/328) had acquired multi-drug resistance. The resistant rate to furazolidone was 68.60%, followed by 42.99% to tetracycline. One vancomycin-resistant E. faecium isolates were isolated from feed origin and 2 from manure origin, with minimum inhibitory concentrations to vancomycin of 1,024, 64, and 64 μg/mL, respectively. The MLST outcomes showed that the 275 E. faecium isolates belonged to 11 sequence types (ST) including ST40, ST60, ST94, ST160, ST178, ST296, ST361, ST695, ST726, ST812 and ST1014. The ST of the feed-sourced VRE was ST1014, while the 2 manure-sourced VRE was ST69. ST1014 evolved from ST78, which was the dominant clonal complex in most cities of China, leading to the spreading of VRE. These findings revealed the potential safety hazards of commercial probiotic enterococci in China and showed that there is a risk of the VRE horizontally transferring from feed to food.