Isolation,Identification And Biological Characterization Of Salmonella In Different Pig Herds And Environments In A Company

Salmonella is an important zoonotic pathogen and the second most common cause of foodborne illness in humans.Pork is second only to eggs as the main source of human infection with Salmonella.As China is the largest pig producer and pork consumer in the world,it is important to conduct research on the prevalence distribution and drug resistance of Salmonella in the main stages of pork production to ensure the healthy development of the pig industry and the safe supply of pork products.Farming is the front end of the pork production supply chain,and when pigs are infected with one or more serotypes of Salmonella,they can continuously discharge and cause transmission.In recent years,overuse of antibiotics on farms has resulted in the development of drug-resistant Salmonella,which poses a threat to human clinical treatment.There are still limited systematic studies on the epidemiological distribution of Salmonella in different pig populations and their living environment in the pig breeding chain.In this study,samples were collected from different pig herds and their living environment in a pig farming company for the isolation and identification of Salmonella,and drug susceptibility testing was performed on the isolated strains,and the drug resistance genes and plasmid types carried by the strains were detected,and multi-locus sequence typing(MLST)was performed for multi-drug resistant strains.The main results are as follows:1.Isolation and identification of Salmonella spp.from different pig herds and their growing environmentsIn 2022,1800 samples were collected from different pig herds(anal swabs)and their growing environments(waterers,troughs,sewage and pig pen floor swabs)in a pig farming company and 240 strains of Salmonella were isolated,with an isolation rate of 13.33%.Among the pig samples,the highest isolation rate of Salmonella was found in anal swabs from nursery and fattening pigs,with 37.22%(67/180)and 26.30%(71/270),respectively,followed by anal swabs from sows,with 13.33%(60/450),and the lowest isolation rate of Salmonella was found in anal swabs collected from newborn and weaned piglets stages,both with 0.67%(1/150).Among the environmental samples,the highest isolation rate of Salmonella was found in the floor swabs of pig houses with 13.33%(20/150),followed by trough swabs and sewage swabs with 5.33%(8/150)and 4.67%(7/150),respectively,and the lowest isolation rate of Salmonella was found in waterer swabs with 3.33%(5/150).2.Drug susceptibility testing of SalmonellaThe results of drug susceptibility tests of the 240 isolated Salmonella strains to 10 antibiotics showed that Salmonella had the highest resistance rate to sulfamethoxazole(96.25%),followed by flupenthixol(82.08%),tilmicosin(64.58%)and amoxicillin(55.42%).Salmonella also showed some degree of resistance to enrofloxacin,gentamicin and ceftiofur,but all were less than 20%,and were sensitive to three antibiotics,tigecycline,polymyxin E and imipenem.Multiple resistance results showed that 72.50%of the tested Salmonellae were resistant to three or more antibiotics.3.Analysis of drug resistance genes and plasmids carried by SalmonellaDrug susceptibility testing showed that the percentages of resistance of 240 Salmonella strains to sulfamethoxazole,flupenthixol,tilmicosin and amoxicillin were 96.25%,82.08%,64.58%and 55.42%,respectively.Of the 240 Salmonella strains,174(72.50%)showed multi-drug resistance,and among the multi-drug resistant strains,the highest percentage of Salmonella was 52.5%,which was resistant to sulfonamides,macrolides and fluoroquinolones.4.Multilocus sequence typing(MLST)of multidrug-resistant SalmonellaMulti-locus sequence typing analysis was conducted for 174 multi-drug resistant strains,and seven ST types(ST19,ST29,ST34,ST40,ST365,ST469 and ST7612)and one new ST type were identified,with ST365(24.71%,43/174),ST469(24.14%,42/174),ST34(22.99%,40/174)and ST29(20.69%,36/174)had the highest percentage of dominant ST types.In conclusion,this study found that the isolation rate of Salmonella isolated from nursery and fattening pigs in this pig farming company was high,and the feeding management and prevention and control of Salmonella should be strengthened for these two groups.In addition,Salmonella was also isolated in the farming environment,suggesting that sanitary disinfection of the environment should be strengthened.This study also found that the Salmonella isolated in this company showed more serious drug resistance,suggesting that attention should be paid to the scientific and rational use of drugs in the process of feeding management.