Increased Susceptibility toEscherichia coliInfection in Mice Pretreated withCorynebacterium parvum

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Abstract
The contribution of activated macrophages to protection against E. coli was studied in mice treated i.v. with C. parvum [Propionibacterium acnes] 7 days before infection. C. parvum-treated mice showed increased phagocytic activity and enhanced resistance to Listeria infection. These mice showed increased susceptibility to a subsequent challenge with E. coli that correlated with a reduction in the LD50 of lipopolysaccharide (LPS) in these mice. The peritoneal macrophages obtained from C. parvum-treated mice had a strong ability to phagocytize and kill E. coli in in vitro experiments. A rapid decline in the number of bacteria in the liver of C. parvum-treated mice was observed in the early period of infection. The number of bacteria in liver and spleen increased progressively to a lethal dose from 6 h after infection. At this time, a significant increase in .beta.-glucuronidase, a lysosomal acid hydrolase, was found in the serum of these mice. In vitro experiments revealed that the peritoneal macrophages from C. parvum-treated mice were highly susceptible to the cytotoxic effect of LPS after 6 h of incubation with LPS. Apparently, the hypersensitivity of activated macrophages to the cytotoxic effect of endotoxin derived from E. coli may be partly responsible for the increased susceptibility of C. parvum-treated mice to E. coli infection.