Characterization of endotoxin from the rumen bacterium Megasphaera elsdenii

Phenol-water extraction of Megasphaera elsdenii, a predominant gram-negative coccus in rumens of cattle fed high-grain diets, yielded material that exhibited typical characteristics of endotoxin. The extract was lethal to mice and to chicken embryos, caused biphasic fever in rabbits, leukopenia in mice, and local and generalized Shwartzman reactions; and induced tolerance to the lethal effect of the endotoxin in mice. The material contained carbohydrate, protein, lipid, phosphorus, and 2-keto-3-deoxyoctonate, but no nucleic acid. The beta-hydroxymyristic acid was absent. Results imply that M elsdenii endotoxin has many biological and chemical characteristics common to enterobacterial endotoxin. However, the median lethal doses in mice and in chicken embryos, and minimal dose required to elicit a local Shwartzman reaction, indicate that M elsdenii endotoxin's potency is low, which may explain why the large gram-negative bacterial population in the rumen of cattle is generally innocuous.