Induction of Resistance by Listeria monocytogenes Cell Wall Fraction.

A crude cell wall fraction of Listeria monocytogenes was prepared by sonic disruption and differential centrifugation of viable, washed cultures. When injected into mice, this sterile, crude cell wall fraction protected mice against an intraperitoneal challenge with 18 to 85 50% mean lethal dose of L. monocytogenes. Resistance was greatly enhanced when bacterial endotoxin (lipopolysaccharide) was injected along with the cell wall fraction. Resistance was measured both by enumerating the bacteria in the livers and spleens of vaccinated and control mice and by survival studies. Two major lines of evidence suggest that the resistance induced by cell wall fraction is at least in part specific. Unlike non-specific resistance, the cell wall fraction-induced resistance was relatively long-lived, (i.e., it was demonstrable 6 weeks after the last injection of cell wall fraction and lipopolysaccharide). In addition, cell wall fraction protected against challenge with L. monocytogenes, but not against challenge with S. typhimurium.