Study on the Promotion of Bacterial Biofilm Formation by a Salmonella Conjugative Plasmid and the Underlying Mechanism

To investigate the effect of the pR ST98 plasmid, originally isolated from Salmonella enterica serovar Typhi ( S. Typhi ), on biofilm (BF) formation, we carried out in vitro experiments using S. Typhi , Salmonella enterica serovar Typhimurium ( S. Typhimurium ) and Escherichia coli ( E. coli ). We further explored the effects of pR ST98 in vivo by establishing two animal models, a tumor-bearing mouse model and a mouse urethral catheter model. Moreover, we examined the relationship between the quorum-sensing (QS) system and pR ST98 -mediated BF formation. These studies showed that pR ST98 enhanced BF formation in different bacteria in vitro . In both animal models, pR ST98 promoted BF formation and caused more severe pathological changes. It was previously reported that Salmonella senses exogenous N-acylhomoserine lactones (AHLs) through the regulatory protein SdiA and regulates the expression of genes including the virulence gene rck , which is located on the virulence plasmid of some serotypes of Salmonella . In this study, we confirmed the locus of the rck gene on pR ST98 and found that AHLs increased rck expression in pR ST98 -carrying strains, thereby enhancing bacterial adherence, serum resistance and bacterial BF formation. In conclusion, the Salmonella conjugative plasmid pR ST98 promotes bacterial BF formation both in vitro and in vivo , and the mechanism may relate to the AHL-SdiA-Rck signaling pathway.