Prevalence And Characterization Of Shiga Toxin-producing Escherichia Coli During Processing In Chinese Beef Processing Plants

Shiga toxin-producing Escherichia coli(STEC)is a class of important food-borne pathogens that can cause watery diarrhea,hemorrhagic colitis(HC),hemolytic uremic Syndrome(HUS),and other high mortality rate of disease.Cattle and other ruminants are the main storage hosts of STEC.However,due to the shorter beef industry and the different habit of consumption,China which is the third largest beef-producing nation,is little known of the epidemiological investigation and biological characteristics of STEC in beef cattle slaughtering process,which not only increased the risk of the national edible safety of beef,but also restricted the healthy and rapid development of beef cattle enterprises.This study was carried out to investigate the prevalence of STEC in beef cattle slaughtering process,to evaluate the different stages during processing.Besides,the serotypes,major virulence genes and drug resistance were determined from these STEC isolates.The main results of this study are as follows:In view of the diversity of the samples,the pretreatment and PCR screening conditions of the samples were optimized.The conditions of centrifugal removing impurity were determined as follows: 5000 RCF,6 min.The final PCR reaction conditions were as follows: initial denaturation 94 ? 2min,denaturation 94 ? 30 S,annealing 56 ? 30 s,elongation 72 ? 1min,35 cycles,final elongation 72 ? 10 min.The positive samples of PCR were secondary screened by STEC chromogenic medium and the lobular or purple,halo rounded strains were isolated.A total of 600 samples were collected from six processing points(hide,post-dehiding,post-washing,feces,chilled carcasses and raw meat)of the beef cattle slaughtering process in two plants and 26 positive samples were detected,the total detection rate was 4.33%.For STEC,the positive detection rates of six processing points were 18.0%,4.0%,1.0%,2.0%,1.0%,and 0.0%,respectively.26 strains of STEC were isolated from 600 samples,and double PCR was performed with STX as the target gene.Among them,only 9 strains of stx1 gene were included,accounting for 34.62% of the total isolates;6 strains containing only stx2 gene,accounting for 23.08%;11 strains accounting stx1 and stx2,accounting for 42.31%.The isolated STEC strains were purified by Escherichia coli O antigen.The results show that,16 kinds of serotype were identified in 26 strains of STEC isolates,a total of 24 strains,accounting for 92.31%.The dominant serotypes were O39(6strains)and O76(4strains),accounting for 38.46%,and 2 strains were not determined.The susceptibility of STEC isolated to antibiotics was analyzed by Kirby-Bauer method.The results showed that 26 strains of STEC had high resistance to tetracycline,ampicillin,cephalosporin,cefuroxime,ampicillin sulbactam and SMZ-TMP,the resistance were 30.77%,26.92%,23.08% 23.08%,19.23% and 19.23%,and 26.92% of the strains showed multiple drug resistance.The sensitivity of fosfomycin was the highest,the sensitivity was 96.15%,followed by ciprofloxacin(80.77%),nitrofurantoin(76.92%)and SMZ-TMP(73.08%).