Study On The Prevalence And Prevention Of Salmonella In Pork Production Chain

Salmonella infection is an important zoonotic disease.Pig is one of the main hosts of Salmonella.Human is being infected with Salmonella,which seriously threatens human health,after consuming contaminated pork or pork products.Pig farms,slaughterhouses and markets are the major sites for the contamination,and spread of Salmonella from pigs.Therefore,it is essential to strengthen the inspection and prevention of Salmonella in the pork production chain.At present,there are limited domestic research on the contamination of Salmonella in the whole pork production chain,and past studies have not focused on prevention and control measures.This study investigates the contamination of Salmonella and the distribution of serotypes in all aspects in the pork production chain,and uses Multilocus sequence typing(MLST),Pulsed Field Gel Electrophoresis(PFGE),Whole Genome Sequencing(WGS)and other methods for molecular typing of strains to identify the critical control points and the main contamination method.On the basis of classification research,research on prevention and control in slaughtering,transportation and market segments.Adding spraying facilities in the slaughtering process,increasing the disinfection times in the transportation process,and using nanomaterials in the market meat products for the Salmonella prevention.Control test to prevent and control Salmonella in the pork production chain.In the future,it can be applied in actual production to reduce the prevalence of Salmonella in the pork production chain.1.The prevalence of Salmonella in the pork production chainBetween July 2017 and December 2018,samples were taken from a large pig farm in Jiangsu,a large semi-automated pig slaughterhouse and its downstream supermarkets.Altogether 950 samples,including 80 samples of farm manure samples.There are 400 samples of carcass wipes in the slaughterhouse,70 samples of slaughterhouse environment samples,equipment wiping samples and transport wiping samples.The supermarket samples include 200 pork samples and 200 bone samples.Totally 417 strains of Salmonella were isolated,with a total separation rate of 43.9%.The Salmonella segregation rate of pig manure samples is at the lowest level(28.8%)in the whole pork production chain.The isolation rate of Salmonella increased to(47.0%),and this may be due to cross-contamination caused by increased excretion due to stress response during pig transport.The isolation rate of Salmonella in the middle part of the sputum reached the highest(51.0%),which may be due to the contamination of the semi-tool and the contents of the corpus callosum;The spraying process reduced the separation rate of the carcass modification to 33.0%;the isolation rate of Salmonella in the cold storage was reduced to 23.0%,which may be caused by the bacteriostatic effect of lactic acid spray and cryopreservation before storage.Environmental samples such as slaughterhouse ground,knives,and transport vehicle wiping samples have a total separation rate of 18.6%.All the 400 samples were collected in the supermarket section,and 227 strains of Salmonella were isolated.The total separation rate was 56.8%.The separation rate of pork samples was 50%,and the separation rate of pork bone samples was 63.5%.The phenotype of 417 strains of Salmonella isolated was determined by Kauffmanne-White method.The results showed that the most superiority serotype in the pork production chain was Salmonella Derby(35.1%),followed by Salmonella Typhimurium(31.0%).Both Salmonella were detected in each sampling.The other detection rates were higher by Salmonella London(10.3%)and Salmonella Rissen(8.4%).The remaining Salmonella serotypes included Salmonella Thompson,Salmonella Reading,Salmonella Enteritidis,etc.The separation rate did not exceed 2.0%.2.Molecular typing and control of Salmonella in the pork production chainUsing MLST to classify 202 strains of S almonella and there were totally 10 ST types.Among them,ST40,ST34,ST469 and ST155 were detected in the farm,slaughterhouse and market in the pork production chain.ST40 accounted for 37.1%and ST34 accounted for 35.9%.ST155 and ST469 were 13.4%and 11.9%.There is a one-to-one correspondence between ST type and serotype.67 strains of Salmonella Derby in the MLST trial were selected for PFGE typing.The results showed that Salmonella elegans from the same source had high similarity and similarity was greater than 85%.Strains with greater than 85%similarity were found in different stages of the slaughterhouse,and strains from different sources also had a similarity greater than 85%,while strains greater than 85%similarity were considered to be homologous strains.The above results indicate that Salmonella spreads pollution along the production chain,and there may be colonized bacteria in the slaughterhouse,causing continuous pollution to the carcass.Cause PFGE is a single enzyme cleavage site for the Salmonella genome,plasmid transfer between strains,deletion or increase of movable elements such as transposons,and homologous recombination of fragments cannot be revealed by PFGE experiments.Because of its high resolution and comprehensive functions,WGS can conduct an epidemiological analysis of Salmonella by sequencing with large batches as the cost of sequencing is reduced.PFGE can't detect plasmid transfer in the genome of the strain,deletion and insertion of movable elements such as transposons,and homologous recombination,in order to trace the source of Salmonella in the pork production chain and find key control points in the pork production chain,the same strain of Salmonella Derby strains in the PFGE test was selected for the WGS test.By plotting the maximum likelihood tree of 367 housekeeping genes on the genome,Salmonella from different sources was found in the same cluster of trees,indicating that different sources can be derived from evolutionary phylogenetic or genomic similarity.Salmonella is spread through the pork production chain.This study further confirmed from the genome level through the WGS analysis that the downstream strains in the pork production chain are upstream strains that spread downstream along the pork production chain,and the colonization bacteria in the slaughterhouse are mainly found in various knives during the slaughtering process where the cross-contamination occurred.The results of PFGE and WGS show that the slaughterhouse and the transport vehicles are the key control points for reducing Salmonella contamination in the pork production chain.Targeted prevention and control measures are proposed for these key control points in combination with the production practice of the production enterprises.Among them,the sprinkling facility was added after the second half of the slaughtering process,and the carcass was sprayed twice.The spraying rate was reduced from 51%to 33%.In the transportation process,the disinfection after the unloading of the goods is increased to two times after the unloading and before the reloading,and the disinfection is carried out by using 2%sodium hydroxide solution and 1%hydrogen peroxide solution.After the disinfection measures,the isolation rate of Salmonella porcine decreased from 60.8%to 50.6%.In view of the high rate of pork infection in the market,a bactericidal effect of meat products in the market was studied using an imidazole salt nanomaterial with good bactericidal effect.The pork was treated with nanomaterials,and the bacteria were eluted for plate counting.The results showed that the nanomaterial treatment reduced the bacterial load of the pig by 40 times.The above measures have effectively reduced the isolation rate of Salmonella in the pork production chain,especially the new nanomaterials provide a new idea for the prevention and control of Salmonella.