Analysis of contamination and pathogenic characteristics of Salmonella in the processing of pre-packed cooked meat products

ObjectiveTo analyze the molecular characteristics and antibiotic susceptibility of Salmonella isolates and investigate the contamination of Salmonella in pre-packed cooked meat products during food processing.MethodsAccording to the sampling requirements of the national “Manual for Monitoring the Production and Processing of Cooked Meat Products （Pre-packed）”， 460 environmental and cooked meat samples were collected from a pre-packed cooked meat product factory in Dezhou from 2015 to 2017. Salmonella isolation and identification were performed per the currently effective GB 4789.4—2016 protocol. Salmonella serotypes were determined based on serum agglutination. Pulsed field gel electrophoresis （PFGE） and multilocus sequence typing （MLST） were employed to determine the molecular types of Salmonella isolates. Resistance tests for 15 antibiotics were performed using the broth microdilution susceptibility test.ResultsThe detection rate of Salmonella in 460 samples was 5.65% （26/460）. The detection rate in 2016 was the highest （7.65%， 14/183）， and the difference among samples from different years was not statistically significant （χ2=2.82， P>0.05）. The detection rate in intermediate products was the highest， and the difference among samples from different samples was statistically significant （χ2=64.16， P<0.05）. Salmonella was detected only in the raw product workshop， and the difference among samples from different workshops was statistically significant （χ2=78.08， P<0.05）. Twenty-six strains of Salmonella were divided into six serotypes， with Salmonella enteritidis being the most prevalent， accounting for 53.85% （14/26）. Twenty-six isolates were subtyped into 12 PFGE types， with type S4 predominantly dominating. The 26 Salmonella strains were divided into five types based on MLST typing. ST11 was the major ST type. Of these 26 isolates， 22 were resistant to various antibiotics. The highest antibiotic resistance rate was for ampicillin， at 73.08% （19/26）， and the multiple antibiotic resistance rate （resistance to three or more antibiotics） was 73.08%.ConclusionDuring the processing of cooked meat products， Salmonella contamination is concentrated mainly in raw materials and intermediate products. The contamination status of the products after steaming was effectively controlled.