Prevalence And Characteristics Of Salmonella In The Whole Layer Production Chain And Evaluation Of Germicidal Efficacy Of Disinfectants

Salmonella is a common foodborne pathogen in poultry production system.Contaminated poultry and poultry products are crucial sources of human salmonellosis.Salmonella exists at different stages of poultry production,some serotypes can be colonized in the intestinal tract and migrated to other organs,such as fallopian tubes,digestive tract,etc.,which can persist in the environment,resulting in vertical and horizontal transmission and contaminating the food industry along the production line.It is necessary to understand the contamination condition and characteristics of Salmonella in poultry production in order to study the effective intervention measures.Through epidemiological investigation and molecular typing,this study reveals the epidemic law,drug resistance and genetic characteristics of Salmonella in the production chain,in order to find out the transmission mode and critical control points of Salmonella along the production chain of laying hens,so as to provide the necessary data for the prophylaxis and treatment of Salmonella in poultry industry1 Analysis of epidemic status and drug resistance of Salmonella in production chain of laying hensIn this study,a poultry egg industry chain enterprise in Jiangsu Province was selected to collect samples from September 2017 to November 2019.A total of 703 breeder serum samples and 1,249 etiological samples were collected.The sampling process includes feed farms,breeding farms,hatchery,egg collection centers and egg processing plant.The sample types are feed raw materials,weak chicks,sick and dead chickens,eggs,dead embryo eggs,egg products and environmental samples.Results of antibody detection turns out that the positive rate of Salmonella O9 antibody in serum was 22.2%.132 of the etiological samples were Salmonella positive,with an average isolation rate of 10.6%.The Salmonella isolation rate was significantly different in different production stages,among which the egg company had the highest isolation rate(34.1%),followed by the egg collection center(16.4%).The isolation rates of other links were lower,including 8.9%in hatchery,4.8%in feed factories,and 2.7%in farms.132 Salmonella isolates were serotyped and 7 serotypes were successfully identified.The dominant serotypes are Salmonella Enteritidis(60.61%)and Salmonella Infantis(29.6%),and the rest accounted for 9.9%.The results of antibiotic resistance test showed that the resistance to nalidixic acid and tetracycline was the highest,which was 63.9%and 63.1%respectively,followed by streptomycin(57.7%),ampicillin(56.2%)and amoxicillin(24.6%),and others were less than 8.0%.The drug resistance rates vary at different production stages,the breeding farms and hatchery were higher,while those of isolates from egg collection centers were lower.2 Study on molecular typing of Salmonella in production chain of laying hensIn this study,aiming at the Salmonella isolates in the whole industry chain of laying hens,the epidemic relationship of Salmonella in different production links was understood by PFGE and WGS,and the phylogenetic tree was drawn according to the genomic differences to explore the source and pollution law of Salmonella.22 strains of S.Enteritidis and 13 strains of S.Infantis were selected from different links and different isolation time for WGS analysis.At the same time,35 strains of S.Enteritidis from different links of the whole industry chain of laying hens were genotyped by PFGE.WGS analysis showed that the ST type of 22 S.Enteritidis strains were all ST11.95.45%of the strains carried strA,strB,sul and blaTEM-1B,77.3%containing tetA genes.Combined with previous experiments,it was found that the drug resistance genes were consistent with the drug resistance phenotype.The phylogenetic tree showed that the strains of different links were distributed in the same branch which displayed the very close genetic relationship.Combined with epidemiological investigation,S.Enteritidis can spread vertically along the production chain.In addition,PFGE results showed that some strains showed 100%genetic homology,which further confirmed the vertical transmission phenomenon shown by WGS analysis.The whole genome analysis showed that the ST type of 13 strains of S.Infantis was ST32.100%of the strains carried aac(6’)-Iaa and mdf(A).The phylogenetic tree analysis showed that the genomes of 13 strains of S.Infantis in egg products and egg collecting center environment were very similar and belonged to the same clone cluster.Therefore,it is speculated that the S.Infantis transmitted in the industrial chain is the same strain,it can spread along the industrial chain,and there may be the phenomenon of cross-contamination.And the egg collection center is the first time to detect S.Infantis,so it can be seen that the egg collection center is an important control point of S.Infantis.The results of this study show that the increase of clean egg production equipment,regular disinfection of egg grading equipment,egg receptacle,transfer vehicle and staff,and proper change of disinfectant in egg washing equipment are very important for the prevention and control of Salmonella.In this experiment,the reduction ability of six different types of chemical disinfectants to Salmonella was evaluated.All the six disinfectants had certain effects on Salmonella isolates.MIC and MBC did not show disinfectant resistance,and there was no significant difference in the two parameters between different serotypes.Except sodium hypochlorite,disinfectants have germicidal effect at the lowest concentration of inhibiting bacterial growth.The determination of minimum inhibitory concentration will help to select the most effective and economical disinfectant to purify Salmonella in a specific environment.In summary,the Salmonella contamination in the layer industrial chain is more serious,among which S.Enteritidis and S.Infantis are the main serotypes.According to the results of PFGE and WGS,it was found that there was a cloning relationship among the strains of different links.The strain has the phenomenon of vertical transmission,horizontal transmission and cross-contamination.Therefore,in the chicken breeding stage,more stringent measures should be taken to control Salmonella and at the same time increase the disinfection measures for egg collection centers.