Diminished Innate and Acquired Immunity Response to dam Mutants of Salmonella enterica Could be Related to a Defective Lipopolysaccharide (LPS) Synthesis

SARNACKI SH, GIACOMODONATO MN, NOTO LLANA MA, VALVANO MA, CERQUETTI MC.

Orlando, FL, USA.

Congreso; 106th General Meeting of American Society for Microbiology; 2006

American Society for Microbiology

The DNA adenine methylase (Dam) enzyme modulates a variety of processes such as DNA replication, mismatch repair and gene transcription. Salmonella enterica dam mutants have decreased infectivity in the murine model and have been recently suggested as promising vaccine candidates. We obtained Salmonella enterica serovar Enteritidis dam mutants by targeted and transposition mutagenesis. Using a murine model of salmonellosis, we observed that the S. Enteritidis dam mutants were highly attenuated when inoculated by intraperitoneal, oral, and intragastrical  routes. Protection rates conferred by these mutants in immunized mice challenged with the parental strain of S. Enteritidis, varied between 40 to 60 %. We also found that dam mutants induced lower levels (p < 0.05) of intestinal IFN-gamma than the parental strain (509 + 62 vs 798 + 82 pg/ ìg of protein, respectively), measured by ELISA. Western blot analysis showed that dam mutants induced a delayed activation of NF-kB. We also observed by silver-stained SDS-PAGE that dam mutants produce a defective LPS, which was characterized by a reduced length in the O antigen polysaccharide. These observations suggest that the Dam protein may be involved in modulating LPS synthesis, more specifically the length distribution of O antigen polysaccharide, a function encoded by the wzz gene. Therefore, a defective LPS could explain, at least in part, the avirulent phenotype of Salmonella Enteritidis dam mutants.