A total of 126 samples were collected from at least three pigs, including their carcasses, meats, and the associated environments. All samples were collected from the farm to retail stores over four consecutive days in May 2021 to track the transmission of pathogens from their production environments to meat samples.

Specifically, at the barn, samples were collected from the three finishing pigs’ skins, feed, feces, liquid manure, floors, workers’ gloves, and dust fans. At the slaughterhouse, samples were collected from each of the three carcasses, floors, gloves, carcass knifes, washing water, and drain water. At the processing plant, samples were collected from processed meat, floors, water, tables, gloves, and drain water. At retail stores, pork belly and neck meat products were obtained.

Four major foodborne pathogens—Shiga toxin-producing Escherichia coli (STEC), Staphylococcus aureus, Listeria monocytogenes, and Yersinia enterocolitica—were isolated from the collected samples.  Notably, nine STEC strains were isolated from pork belly meat samples at a high rate. Additionally, 12 STEC strains were found in feces at the pig farm, on carcasses and gloves at the slaughterhouse, and in belly meat at retail stores. Other E. coli isolates were found in feces and liquid manure at the farm, the working table at the meat processing plant, and the neck meat at the retail stores. L. monocytogenes and S. aureus were respectively recovered from pork meat and the working table at the meat processing plant, and ten Y. enterocolitica strains were found in the slaughterhouse.

Furthermore, pathogens Proteus mirabilis, Acinetobacter baumannii, and Providencia rustigianii were isolated from retail meats, but not from the farm, slaughterhouse, or meat processing plant. The findings suggest that cross-contamination at stores may be an issue.

Y. enterocolitica, STEC, S. aureus, and L. monocytogenes were tested for AMR. One Y. enterocolitica strain was resistant to ampicillin, and the majority of the STEC isolates were resistant to multiple drugs, specifically ampicillin, kanamycin, streptomycin, sulfamethoxazole, and tetracyline. L. monocytogenes and S. aureus were also shown to be multi-drug resistant (MDR) to ampicillin, erythromycin, and vancomycin. All the important foodborne pathogens were not resistant to critical antibiotics ciprofloxacin and gentamicin.

Through subtyping of the STEC colonies, the researchers found that STEC strains isolated from the samples from the farm, slaughterhouse, and carcasses did not transmit to the pork meats. STEC strains found in the pork meats were likely to be contaminated from the workers or environments at the retail stores. Additionally, STEC isolates from the pork products in retail stores displayed higher rates of AMR than those that at the farm and slaughterhouse. The AMR patterns of STEC isolates reflected commonly used antibiotics in the South Korean pig industry.

The findings of the study affirm that clinically important pathogens can be transmitted at high rates to pork meat products during the slaughtering and processing phases of production. The results may help farmers, stakeholders, and government develop a strategy for reducing the emergence and spread of AMR through pork meat and production environments. The researchers call for proper and prudent use of antimicrobials for pig production to minimize the emergence and development of bacteria that ae resistant to clinically important antibiotics, as well as monitoring of AMR patterns for clinically important pathogens.