Influence of endotoxin on resistance of mice to intraperitoneal infection with human oral bacteria

Abstract

Intraperitoneal injection in mice of mixed cultures of oral bacteria as contained in suspensions of material from the human gingival sulcus leads to a severe bacteremia with viridans streptococci. Eighty to one hundred per cent of such animals succumb within 24 hr. Streptococci alone in suspensions of the same optical density as the mixed cultures are not lethal to mice, but injection of sublethal amounts of heatkilled fusobacteria or veillonellae immediately prior to challenge with streptococci results in a ten-fold decrease in LD 50. Pretreatment with heat-killed gram-negative oral bacteria or sublethal microgram quantities of lipopolysaccharide endotoxins from fusobacteria increases susceptibility to oral streptococci during the first 6–8 hr, followed by a period of increased resistance after 24 hr. This biphasic effect of endotoxin on the resistance of mice to peritoneal infection with oral streptococci has also been substantiated by observations on the duration of the ensuing bacteremia and on bactericidal activity within the peritoneal cavity. The experiments indicate that the pathogenicity of a mixed gingival flora may depend on a decrease of local and systemic defense mechanisms induced by endotoxins derived from gram-negative oral bacteria.