Some structural and biological properties of Brucella endotoxin

Hot phenol-water extraction of smooth Brucella abortus and B. melitensis cells yielded a toxic fraction which was recovered from the phenol phase (fraction 5). Chemically, fractions 5 from both Brucella species were lipid-carbohydrate-protein-2 keto-3-deoxyoctulosonic acid complexes which were stable to heat and resistant to Pronase digestion. Electron micrographs of the Brucella toxins were morphologically indistinguishable from those of enterobacterial endotoxins. Biologically, Brucella toxins were lethal for mice and immunogenic for rabbits. An intravenous injection of Brucella toxin induced severe leukopenia with subsequent leukocytosis in mice. Cross-tolerance experiments with mice demonstrated that pretreatment with B. abortus toxin lessened the hypoferremia produced by challenge with Escherichia coli endotoxin. Furthermore, fractions 5 from B. abortus and B. melitensis were able to form hybrids with E. coli and Salmonella enteritidis endotoxins and also with each other. Although Brucella toxins possess many structural and biological properties in common with endotoxins from the Enterobacteriaceae, some quantitative differences in their biological potencies were observed. Brucella toxins were relatively innocuous in tests for pyrogenicity in rabbits and lethality for chick embryos. In nonspecific protection tests, Brucella toxin had only 1/75 the potency of E. coli endotoxin in protecting mice against challenge with virulent S. typhi. However, on the basis of the data presented and on the work done previously, we concluded that the heat-stable toxins of B. abortus and B. melitensis were endotoxins.