Prevalence Characterization Investigation And Contamination Tracing Of Listeria Monocytogenes In Beef Cattle Processing

L.monocytogenes is one of the four major foodborne pathogenic bacteria.This bacteria exists in all theprocessing procedures during the cattle slaughtering and beef cutting in the abattoirs.As well the environment of the beef cattle plants.When beef was contaminated by L.monocytogenes it may lead to serious food safety problems,and become a serious threat to human health.The aim of this study was to investigate the prevalence of L.monocytogenes in two beef slaughter plants(A and B),and to determine the antibiotic susceptibility,serotype and genetic diversity of isolated strains.It will trace the contaminant source of L.monocytogenes in plants based on the genetic relationship analysis.In the practival view,this study will provide theoretical basis for controlling the contamination of L.monocytogenes in both plants.The main result of this study as following:1.The prevalence of L.monocytogenes in the beef cattle processing plantsThe prevalence of L.monocytogenes was investigated during slaughter process of beef cattle at two beef abattoirs in Shandong province.The sampling points included transport cart,lairage pens,feces,hides,postevisceration carcasses,post-washing carcasses,chilled carcasses and beef cuts.A total of 236 samples were collected from plant A,of which 33 were L.monocytogenes positive with the total detection rate was 13.98%.While a total of 233 samples were collected from plant B,with 108 positive,showingthe total detection rate was 46.35%.The higher detection rate of two plants were chilled carcasses(80%)and beef cuts(81.25%)respectively.2.The antibiotic susceptibility test of L.monocytogenesAccording to the antibiotic susceptibility test of 150 strains L.monocytogenes,it was found that all of the strains were sensitive to gentamicin,kanamycin,erythromycin,tetracycline,trimethoprim-sulfamethoxazole and chloramphenicol;Resistance rates of ampicillin,nitrofurantoin,trimethoprim,rifampicin and clindamycin were 21.99%,0.71%,0.71%,1.42% and 74.47%,respectively.Some strains have multiple drug resistance,with one strains showed 5-multiple resistance and 28 strains double drug resistance.3.Phenotype and genotype of L.monocytogenes isolates from different plantsAll the 150 strains of L.monocytogenes were serotyped by multiplex PCR.Among them,36 strains of L.monocytogenes from plant A were 1/2a,and 114 strains of L.monocytogenes were isolated from plant B were 1/2a as well.A total of 35 strains of L.monocytogenes in plant A were typed by MLST,they were divided into three STs: ST8,ST9 and ST19.The L.monocytogenes isolated from the cattle hides is a single genotype,the L.monocytogenes from environment were traced back to the feces.The STs of samples collected from postevisceration carcasses,post-washing carcasses,chilled carcasses and beef cutskept with those samples from plants environment.The 108 strains of L.monocytogenes were divided into ST9,ST19 and ST121 genotypes from plant B,and those contaminated strains from cattle hides,postevisceration carcasses,post-washing carcasses,chilled carcasses,beef cuts and environment were traced back to lairage pens and feces.Overall,the contaminated sources of L.monocytogenes in beef cattle abattoir were lairage pens,faces and slaughtering environment.