Studies On Virulence Gene Profile And Biofilm Forming Ability Of Salmonella

Salmonella is an important zoonotic and foodborne pathogen,which seriously threatens food safety and public health.The pathogenicity of Salmonella is closely related to the virulence genes it carries,and biofilm formation also plays an important role in the transmission and infection of the pathogen.In this study,we investigated the virulence genes and biofilm formation ability of 243 Salmonella strains of 36 serotypes collected from different regions and sources in China,so as to lay the foundation for further research on the pathogenic mechanism and prevention and control measures of Salmonella.Key findings were as follows:Salmonella genome information was obtained based on whole gene sequencing techniques,which enriched the genetic resources of Salmonella.The average genome size of Salmonella was 4.88 Mb.G+C content ranged from 51.66%to 52.35%,with an average of 52.04%.The predicted number of genes ranged from 4,173 to 5,334,with an average of 4,694.The average length of coding genes was 4.25 Mb,accounting for 87.16%of the genome.Based on the whole genome sequence,the DIAMOND software was used to perform blastp comparison with the virulence factor database to obtain the virulence gene prediction results of Salmonella,and the statistical analysis of virulence genes was performed.A total of 670 virulence genes were predicted from the 243 Salmonella isolates,of which 319 virulence genes were identified with a detection rate of 100%.The genes were further compared with the NCBI Gen Bank database by blastn,nine unique Salmonella genes（spr B,spi C/ssa B,ssa I,ssa O,ssa P,sse E,sse F,sth D,sop D）were screened out.The number of virulence genes in each strain ranged from 417 to501,with an average of 474.The results of functional classification showed that adhesion,effector factor delivery system,immune regulation,motility and nutrition/metabolic factors were the most numerous functional genes,accounting for 84.63%in total.In addition,virulence gene profile of strains was related to serotype,and the virulence gene profiles of strains of the same serotype or serogroup tended to be the same.Factors such as strain source,year and location of isolation can also affect the composition of virulence gene profile.The copy numbers of 319 virulence genes with 100%detection rate were summarized,and the results showed that the virulence genes showed multiple copies and copy number heterogeneity in different strains.According to the annotation results,the source of virulence genes was analyzed,and 351 virulence genes were found to be homologous to other pathogenic bacteria in the genome of Salmonella.Microporous crystal violet method was used to detect the biofilm formation ability of all strains.The results showed that 99.59%of the strains could form biofilms,with OD₅₇₀ranging from 0.13±0.01 to 1.17±0.15.The proportion of weak,medium and strong biofilm forming capacity strains were 72.43%,24.28%and 2.88%,respectively.On this basis,the relationships between Salmonella biofilm forming ability and serotype,isolation source and biofilm forming genes were further investigated.The results showed that there were significant differences in biofilm forming ability of different serotypes（p<0.05）,the strains of S.Havana and S.Hvittingfoss had the strongest biofilm forming ability,and the strains of S.Agona and S.Bovismorbificans had the weakest biofilm forming ability.The effect of strain isolation source on biofilm forming ability was not significant（p>0.05）.The relationships between 37 biofilm forming genes and biofilm forming ability were analyzed.The results showed that 22genes existed in all strains with different biofilm forming ability.The detection rates of pef ABCD and ddh C genes were positively correlated with the biofilm forming ability of strains.In particular,the detection rates of ddh C gene were more than 60%in the biofilm forming strains.