Isolation And Identification Of Porcine Diarrheagenic Escherichia Coli And Evaluation Of The Bactericidal Effect Of Disinfectants

Diarrheagenic Escherichia coli(DEC)is one of the important food-borne bacteria that is pathogenic to human and animals,and can easily cause severe diarrhea in infants and young animals.DEC can be divided into different pathogenic types,which are widely present in the intestines of animals,and may transmit and contamination in such steps as breeding and slaughtering,causing hidden dangers to food safety and threatening public health.However,it is seriously scarce for the monitoring data of DEC in the whole pork production chain,which obviously restrict the conduction of risk assessment of DEC and development of scientific management strategy.So in this study different types of samples were collected from five slaughterhouses in Hubei province or Guangdong province,and the DEC strains were isolated,identified,and characterized by antimicrobial resistance,in order to discuss the transmission regulation of DEC contaminaton in pig slaughter process.Moreover,the DEC isolates were subject to disinfectant sensitivity test and quantative bactericidal test,so as to explore the effective disinfection measure for the prevention and control of DEC in pig slaughter process.The main results are shown as follows:1.Isolation and identification of porcine diarrheagenic Escherichia coliFrom a total of 1315 samples of different types such as rectal swab,carcass swab and pork collected in 2021,23 strains(1.75%)of DEC were recovered,including 22 strains(1.67%)of Enteropathogenic Escherichia coli(EPEC)and one strain(0.08%)of Enterohemorrhagic Escherichia coli/Shiga toxin-producing Escherichia coli(EHEC/STEC),in which 17 EPEC strainsand 1 EHEC/STEC strain(6.43%)were isolated from the slaughterhouse C in Hubei province,4 strains(1.21%)were isolated from the slaughterhouse D in Guangdong province and one strain(0.43%)was isolated from the slaughterhouse A in Hubei province.All the strains were isolated from pig rectal swab samples,and no DEC strain was detected in carcass swab samples,pork samples and environmental samples,indicated that the DEC strain mainly exists in pigs at farm with the dominant pathogenic type of EPEC and seldom cause the ccontamination in pork along the slaughter chain when the specification is operated.2.Antimicrobial sensitivity of the DEC strainsSensitivity of the 23 porcine DEC strains to 9 antimicrobial agents was evaluated by the determination of minimal inhibitory concentrations(MICs)using the microdilution broth method.The results showed that the highest proportions of isolates exhibited the resistance to ampicillin(95.65%),and florfenicol(82.61%),followed by the resistance to aztreonam(30.43%),cefotaxime(26.09%),and gentamicin(21.74%).All strains were sensitive to tigecycline,polymyxin E,enrofloxacin and meropenem.3.Sensitivity of the DEC strains to commonly used disinfectantsSensitivity of the 23 porcine DEC strains to 8 commonly used disinfectants was evaluated by the determination of minimal bactericidal concentrations(MBCs)using the microdilution broth method.The results showed that the MBC value or distribution range of sodium-trichloroisocyanurate,povidone-iodine,potassium hydrogen persulfate,sodium hydroxide,sodium hypochlorite solution,glutaraldehyde aqueous solution,benzalkonium bromide,and ylmethylammonium bromide was 7273 mg/L,2008 mg/L to 4014 mg/L,1004 mg/L to 2007 mg/L,1966 mg/L to 3932 mg/L,1065 mg/L,2560 mg/L to 512 0mg/L,8 mg/L to 64 mg/L,0.35 mg/L to 2.8 mg/L,respectively.All the MBC values were in the effective disinfection concentration ranges recommended by the Agriculture Industry Standard in China,indicating that the eight disinfectants can effectively kill the DEC strains.No correlation between bacterial resistance and disinfectant susceptibility was found in this study.4.The bactericidal effect of different Bai Dusha products on porcine diarrheagenic Escherichia coliThe bactericidal effect of 6 brands of Bai Du Sha products to the porcine DEC strains was evaluated using the suspension quantitative sterilization test.The results showed that significant difference was observed among different products,in which the products of brands S3 and S4 were better than other brands.The optimal bactericidal effect for the brands S3 and S4 was at the concentration of 1:1000 and duration time of 15 min.The effect of the brand S4 product varied by environmental temperature with the optimal effect at 10 ℃.5.The bactericidal effect of Bai Dusha products on the surface of different materialsThe results of the carrier immersion quantitative sterilization test showed that the bactericidal effect of the Bai Dusha products of brands S3 and S4 was significantly different on the surface of the different materials carrier.It was more effective for the bacteria attached on the surfaces of rubber,plastics and stainless steer.While,it was ineffective for the strains attached to cotton,so it is necessary to increase the disinfectant concentration or prolong the disinfection period.