Analysis of the contamination and pathogenicity of Listeria monocytogenes in the process of pre-packed cooked meat production

Abstract

Objective To put forward preventive and control measures for the quality control of pre-packed cooked meat products by investigating the contamination of Listeria monocytogenes during the food processing chain, analyzing of the molecular characteristics and antibiotic susceptibility of Listeria monocytogenes isolates. Methods Four hundred and sixty samples of raw materials, intermediate products, finished products, final products and environmental samples were collected from a pre-packed cooked meat factory in Dezhou during 2015 to 2017. All samples were tested for Listeria monocytogenes based on GB 4789.30-2016. Pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were applied to identify molecular types of Listeria monocytogenes isolates. The antibiotic resistance test on 8 antibiotics was performed by broth microdilution susceptibility test. Results The detection rate of Listeria monocytogenes in 460 samples was 17.61% (81/460) . The detection rate in 2016 was the highest(22.40%, 41/183) and that from different years was statistically different (χ2=7.28, P<0.05) . The detection rate in finished products was the highest(54.17%, 13/24) and the difference among different sample was statistically different (χ2=45.90, P<0.05) ; The detection rate in raw product workshop was the highest(32.50%, 39/120) and the difference among different workshops was statistically different (χ2=40.16, P<0.05) . 81 isolates were subtyped into 15 PFGE types which were largely dominated by type 1. The 71 Listeria monocytogenes strains were divided into 8 types based on MLST typing. ST9 and ST121 were the major ST types. Among the 81 tested strains, 1 strains was resistant to ciprofloxacin and the antibiotic resistant rate was 1.23% (1/81) . Conclusion The cooked meat products may be contaminated by Listeria monocytogenes in all aspects during the whole processing process, and the pollution may continue to exist. Food processing enterprises should take appropriate cleaning and disinfection measures to strictly control product quality, reduce the pollution of processing equipment and finished products, and prevent the occurrence of foodborne diseases.

Keywords

• listeria monocytogenes
• cooked meat products
• food processing chain
• contamination
• pulsed field gel electrophoresis
• multilocus sequence typing
• antibiotic susceptibility