The biological activity of Leptotrichia buccalis endotoxin

Abstract

Endotoxin obtained from Leptotrichia buccalis was found to have potent biological activity. New Zealand white female rabbits were used as the experimental animal. The parameters studied were ld 50, febrile and leukocytic responses, and the dermal Shwartzman reaction. The ld 50 of Lept. buccalis was 93.15 μg/kg with 95 per cent confidence limits of 66.44 and 131.00 μg/kg. Formal probit analysis revealed that the Lept. buccalis endotoxin, compared to Escherichia coli endotoxin, had a relative potency of 19.45 per cent with 95 per cent confidence limits of 13.50 per cent and 28.01 per cent. Lept. buccalis endotoxin was pyrogenic when administered intravenously in a quantity of 0.039 μg/kg, whereas E. coli endotoxin was pyrogenic in a quantity of 0.009 μg/kg. Parallel line bioassay methods applied to the febrile dose-response relationship of the toxins showed that, compared to E. coli, Lept. buccalis had a potency of 11.47 per cent with 95 per cent confidence limits of 9.69 per cent and 13.63 per cent. The quantity of endotoxin necessary to elicit a fever index of 40 cm 2 was estimated as 0.285 μg/kg and 2.099 μg/kg for E. coli and Lept. buccalis endotoxins, respectively. A significant correlation was found between febrile response and fever index. The quantity of endotoxin needed to produce a 50 per cent reduction in circulating leucocytes was estimated as 0.030 μg/kg and 0.213 μg/kg for E. coli and Lept. buccalis, respectively. According to this bioassay, Lept. buccalis endotoxin had a relative potency of 20–37 per cent, with 95 per cent confidence limits of 9.15 per cent and 43.60 per cent. The dermal Shwartzman reaction revealed that both E. coli and Lept. buccalis endotoxins contained preparatory and provocative factors. E. coli endotoxin was somewhat more potent, and heparin treatment prevented the Shwartzman reactions. The theoretical implications of the presence of endotoxin in Lept. buccalis are discussed in relation to the taxonomy of this micro-organism, and Vincent's necrotizing stomatitis.