| The Salmonellae belong to the family Enterobacteriaceae and are a medically important pathogen for both humans and animals.Salmonellae form a complex group of bacteria consisting of two species and six subspecies and include more than 2600serovars.Serotypes in what is now S.enterica subspecies enterica are the predominant pathogens associated with birds and mammals,which pose a serious threat to poultry industry and public health.S.Enteritidis,S.Typhimurium,S.Pullorum and S.Gallinarum are the four major Salmonella serotypes that cause Salmonellosis in poultry.S.Enteritidis and S.Typhimurium have a broad host range with the ability to cause infections in humans through the food chain,they are important zoonotic Salmonella serotypes.In contrast,S.Pullorum and S.Gallinarum are host-adapted serotypes with a restricted host range,in which they are typically associated with poultry.And the two serotypes can cause serious diseases in chickens,as a result,causing huge losses to the poultry industry.In this study,Salmonella isolates were isolated from the samples,containing feces,brain,liver and spleen of dead or sick chickens,which were collected from poultry farms in Central China during the period of 2013 to 2018.With reference to the diagnostic technical standards for animal salmonellosis in Chinese agricultural industry,a multiplex PCR methods were used to detect four important Salmonella serotypes?S.Enteritidis,S.Typhimurium,S.Pullolum and S.Gallinarum?associated with poultry infection.Finally,we identified 54?64.3%?strains of S.Pullorum,11?13.1%?strains of S.Typhimurium,14?16.7%?strains of S.Enteritidis and 5?5.9%?strains of other Salmonella serotypes,however,no strains of S.Gallinarum were found.Analysis about the prevalence trend of different Salmonella serotypes in poultry farms in Central China showed that S.Pullorum,S.Enteritidis and S.Typhimurium might be the the main Salmonella serotypes that have spreaded in poultry farms in recent years in Central China.Notably,S.Pullorum might be the most serious serotype associated with chickens infection in Central China.These results will provide important guidance for the further prevention and control of Salmonella in those poultry farms.Considered with the importance of virulence genes contributing to the abilities of invasion and pathogenicity of Salmonella,27 virulence genes?sodC1,spvC,spvB,spiA,pagC,cdtB,msgA,invA,sipB,prgH,spaN,orgA,tolC,iroN,sitC,lpfC,sifA,sopB,sefA,pipA,ttrC,misL,siiE,mgtB,spi4D,shdA,sopE?of 84 strains of Salmonella isolates were detected by PCR.The result showed that presence rates of four virulence genes were different from others.The presence rate of sodC1 was98.8%as well as sefA,sopE was 96.4%,cdtB was not present in any isolates,and all the remaining genes were idendified in 84 Salmonella isolates with the rate of 100%.On the basis of the distribution of these virulence genes,the 84 Salmonella isolates were classified into 4 virulence genotypes.The major genotypes,which comprised96.4%of all isolates,included isolates that carried 26 of the virulence genes assessed.The results will help in the study of the correlation between virulence genotypes and pathogenicity.Salmonella serotypes have expanded their host ranges through the acquisition of new genes through horizontal gene transfer,which in turn provide genetic factors that increase the ability to infect new hosts.Therefore,the virulence genes carried by Salmonella virulence plasmids and bacteriophages have played important roles in Salmonella pathogenicity.Based on the above studies,we also established a multiplex PCR assay for Salmonella phage and virulence plasmid-related virulence genes?sodC1,spvB and spvC?.The multiplex PCR assay has a minimal detection limit of10-1 ng/?L for Salmonella genomic DNA,enabling rapid detection of these three virulence genes in Salmonella,and this method will also help in the further study of molecular diagnosis of pathogenic Salmonella. |
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