Assessment of contamination and drug resistance profiles of non-typhoid Salmonella in pig slaughtering industry in Shandong Province

ObjectiveTo understand the contamination and drug resistance characteristics of non-typhoidal Salmonella （NTS） during pig slaughter.MethodsA total of 170 carcasses and environmental samples were collected from two large-scale pig slaughterhouses in May and August 2021 in Shandong Province， China. Whole genome sequencing （WGS） combined with bioinformatics was used to analyze the data of the NTS isolates.ResultsNTS was detected in 29 of 170 pork samples， detection rate was 17.1%. Salmonella typhimurium was the predominant serotype （58.6%， 17/29） in the samples. The results of the drug sensitivity analysis showed that 29 NTS strains had 15 drug resistance spectra， with the highest rate of tetracycline resistance （100.0%， 29/29）， followed by ampicillin and chloramphenicol （79.3%， 23/29）. The multidrug resistance rate was 86.2% （25/29 patients）. Multilocus sequence typing （MLST） showed that ST19 was the main type， accounting for 48.3% （14/29） of cases. Analysis of drug resistance genes showed that they carried mainly tet（A）， tet（B）， tet（M）， blaTEM-1B， blaCMY-97， floR， cmlA1， etc.ConclusionThe phenomenon of NTS contamination exists in some pig slaughterhouses in Shandong Province. NTS has shown resistance to multiple antibiotics， suggesting that attention should be paid to the prevention of NTS in pig slaughterhouses.