In order to investigate the effects of porin genes ompW,ompS and ompD on the biological properties and virulence of Salmonella typhimurium,the corresponding mutant strains were con-structed using the λ Red homologous recombination system,and the growth curves,motility,bio-chemical properties,in vitro genetic stability,biofilm-forming ability,drug resistance,and lethal dose at half capacity(LD50)between the standard strain and each mutant strain were detected by comparative assays for Salmonella typhimurium.The results showed that,compared with the standard strain,the ompD and ompW mutation had less effect on the growth rate and motility of the bacteria,while the ompS mutation significantly reduced the growth rate and motility;none of the three genetic mutation affected the biochemical characteristics of Salmonella typhimurium,nor the genetic stability,but affected its susceptibility to a variety of commonly used antibiotics to varying degrees and caused a highly significant decrease(P＜0.01)in the ability to form a biofilm,and the results showed that the three mutant strains had a significant reduction in the ability to form a biofilm.The result of LD50 virulence assay showed that all three genetic mutation led to a decrease in the virulence of Salmonella typhimurium,among which the ompS mutant strain showed the most obvious decrease in virulence,LD50 was 25 times that of the standard strain.In conclusion,mutations of the pore protein ompW,ompS,and ompD genes can affect some biological properties of Salmonella typhimurium.The results of this study laid an experimental foundation for further research on the biological functions of the pore protein ompW,ompS and ompD genes and Salmonella pathogenicity.