Effect of the quality of the lipopolysaccharide on mouse virulence of Salmonella enteritidis.

The cell wall O antigen is known to affect mouse virulence of Salmonella. We have shown earlier that S. typhimurium expressing somatic antigen 9,12 is less virulent than its 4,12 sister transductants in mice after intraperitoneal inoculation, suggesting that the 4,12-type O antigen is connected with high virulence in mice. In this report we show, in accord with this suggestion, that when the naturally occurring O-9,12 S. enteritidis is made O-4,12 by transduction, its virulence is increased. The difference between O-9,12 and O-4,12 sister transductants is highly significant, with P less than 0.001.