Bactericidal activity in the pig roundworm Ascaris suum

A potent, humoral, bactericidal activity against Micrococcus luteus was discovered in pseudocoelomic fluid of the pig roundworm, Ascaris suum. The activity, which was not bacteriolytic, was not due to lysozyme or to a dietary antibiotic. It was not inactivated by exposure to 100 degrees C, to low or high pH, or to ethanol. Dialysis, electrophoresis and agar-diffusion experiments suggested that the main antibacterial activity in the fluid was associated with a basic substance of molecular weight somewhat less than 14,000 Da. Two other Gram-positive organisms, Bacillus megaterium and Staphylococcus aureus, were also killed by the Ascaris fluid, but the Gram-negative Escherichia coli, Proteus vulgaris and Bordetella bronchiseptica were insensitive.