Signature-tagged mutagenesis screening revealed the role of lipopolysaccharide biosynthesis gene rfbH in smooth-to-rough transition in Salmonella Enteritidis

Salmonella enterica serovar Enteritidis (S. Enteritidis, SE) is a major cause of foodborne diseases for humans. The completeness of the O-chain antigen of Lipopolysaccharide (LPS) determines whether a S. Enteritidis strain is smooth or rough. However, genes that are involved in the synthesis of LPS and rough-smooth variation are not completely understood. In this study, we used monoclonal antibody against O-antigens (O9 mAb) to identify novel factors that are involved in LPS synthesis and rough variation in S. Enteritidis by using signature-tagged mutagenesis (STM) technique. Our results showed that transposon insertion in the gene rfbH led to different LPS phenotype, auto-aggregation characteristic, motility and resistance to environmental stress compared with SE wild-type strain C50041. In addition, sera tests showed that rfbH mutant does not elicit specific antibodies against O-antigens in vaccinated animals. Taken together, the S. Enteritidis rfbH gene is implicated in LPS biosynthesis, rough variation, sera distinguishable reaction, motility and stress resistance. The rfbH mutant strain could be potentially used as a distinguishable vaccine or a live vector to deliver drugs and antibodies in vivo.