Studies on the effects of bacteria on experimental schistosome infections in animals

The initial discovery of the schistosomicidal effects of Klebsiella and E. coli on mice infected with S. mansoni is described. This antischistosomal effect was confined to Gram-negative organisms. The bacteria found to possess this property belonged to the genera: Klebsiella, Escherichia, Salmonella, Arizona, Enterobacter, Serratia and less frequently to the genera Providencia, Achromobacter and Flavobacterium. Of the 24 Gram-positive and 9 other Gram-negative organisms examined none had a lethal effect on the schistosomes. The activity of Klebsiella E.15 and E.10 against strains of S. mansoni from Egypt, Liberia and St. Lucia in mice and hamsters was similar. Klebsiella E.15 was also effective against an Egyptian strain of S. mansoni in monkeys (Erythrocebus patas) and against a South African strain of S. mattheei in mice and hamsters. Activity is confined to mature schistosomes. Immature flukes of 3 weeks or less were unaffected. The rate of activity, the infection and death of the schistosome and the dose response relationship, i.e. the number of organisms given, the route of administration and the resulting kill of schistosomes are described. The precise mode of action on the schistosome is unknown. Living bacteria are essential to produce this effect. Dead bacteria of an active strain and extra-bacterial products were inactive. The effect of antibiotics on the bacterial infection of schistosomes and the interaction between the bacteria and the host are discussed. A freeze-dried preparation of Klebsiella E.10 when ampouled and kept under vacuum at 4°C for 30 months retained its viability and schistosomicidal activity. Some of the problems involved in contemplating the use of bacteria to control schistosomiasis are discussed. The possible inter-relationship between concomittant salmonellosis and schistosomiasis is briefly discussed.