Lysis of Echinococcus granulosus by surface-active agents in bile and the role of this phenomenon in determining host specificity in helminths

Abstract

An extract of ox bile was found to lyse protoscolices of Echinococcus granulosus and induce abnormal accumulations of cytoplasmic fat. This observation led to a study of the in vitro action of bile and bile salts on this organism. Bile from the following herbivores caused lysis and fat accumulations: hare, rabbit, ox, sheep, man; lysis did not occur with bile from the following carnivores: fox, dog, cat. Sodium salts of deoxycholic, glycodeoxycholic and taurodeoxycholic (in order of effectiveness) had a lytic effect. As a rule, herbivore biles producing lysis were those described as being rich in deoxycholic acid, largely conjugated with glycine. Bile from the dog (the natural definitive host) is reported as being relatively poor in deoxycholic acid which in carnivores is largely linked with taurine. It is suggested that the nature, type of conjugation and concentration of bile acids may play (amongst other factors) a major role in determining host specificity for E. granulosus. This hypothesis may prove to be capable of further extension to include intestinal parasites in general and may represent a fundamental controlling factor in many helminth and protozoan life cycles. It follows that the molecular configuration of the exposed surfaces of a successfully established intestinal parasite must be such that it is not susceptible to attack by the lytic agents present in the bile of its definitive host. It is suggested that the mechanism of lysis may be related to the presence of mitochondria in the cestode cuticle since these structures are known to be readily fragmented by deoxycholate and surface active substances. Sodium oleate had a lytic effect similar to, but less rapid than, sodium deoxycholate. There is evidence that the deoxycholic acid content of carnivore bile which is related to the microflora of the gut may be increased by change to a herbivorous diet; if this result is confirmed, it may indicate a nutritional method for controlling E. granulosus in dogs and possibly other helminth infections. It is speculated that a survey of bile acids and bile soaps throughout the animal kingdom may reveal the existence of other surface-acitve agents with a more pronounced lytic effect on E. granulosus or other helminths, than the limited group of bile compounds examined here.