Isolation,Identification And Molecular Typing Of Salmonella From Chicken And Swine In Shanghai And Surrounding Areas

Salmonellosis is a zoonotic infectious disease caused by Salmonella spp which can be transmitted horizontally through contaminated feed and water,or vertically from infected female livestock to offspring.Salmonella could infect a variety of animals and causd diseases,such as chicken typhus,chicken paratyphoid,pig paratyphoid and human causing food poisoning,typhoid and paratyphoid fever and other diseases through contaminated meat and eggs.Therefore,it is necessary to investigate the epidemiology and molecular typing of Salmonella.This study collected 641 samples from farms,supermarkets and other places for Salmonella isolation and investigation.They were isolated by enrichment media and selective medium.PCR was used to identify whether the suspected strains were Salmonella.Then the prevalence of Salmonella in Shanghai and surrounding areas was studied by testing for serotypes,virulence genes and drug resistance.This study carried out on 641 samples and 69 strains of Salmonella were isolated,with isolation rate of 10.76%.Among154 pork samples,15 strains of Salmonella were isolated,with isolation rate of 9.7%.No Salmonella was isolated from 66 samples of pig manure.Fifty-four strains of Salmonella were isolated from 226 dead chicken embryo samples,with isolation rate of 26.11%.No Salmonella was isolated from 195 egg samples.The serotypes of Salmonella isolates were identified by multiplex PCR.A total of 54 strains of Salmonella pullorum,2 strains of Salmonella typhus,7 strains of Salmonella enteritis and 6 strains of other serotypes were identified.The antimicrobial sensitivity test using k-b card method showed that the resistance rate of Salmonella isolates was 100% to clindamycin and rifampicin,and more than 50% to erythromycin,ampicillin,tetracycline,chloramphenicol,azithromycin and cefradine.The multiplex PCR method was used to detect virulence genes of Salmonella isolates.The results showed that the distribution rate of hil A,spi A,ssa R,spi C,sif A,mgt B,mis L,spi4 D,pip A,pip B,sop B and pag N genes was 98.55%,the distribution rate of spo E is92.75%,the distribution rate of ssr A is 97.10%,and the distribution rate of shd A is20.29%.MLST and CRISPR were used to classify Salmonella isolates.The results showed that the isolated 69 strains of Salmonella were divided into 7 ST types,namely ST11,ST19,ST34,ST40,ST42,ST92 and ST155,the ST92 was the dominant ST type.All the Salmonella isolated in this study were CRISPR1 type.These results showed that the isolation rate of Salmonella spp infection in Shanghaiand surrounding areas was relatively high,among which Salmonella pullorum wananas prevalent in chicken samples and Salmonella enteritis in pig samples.These Salmonella isolates contain multiple virulence genes.The molecular typing of Salmonella isolates in Shanghai and surrounding areas is mostly consistent.These Salmonella isolates are resistant to common antibiotics.