PHAGOCYTIC DEFENSE BY THE EARTHWORM EISENIA-FOETIDA AGAINST CERTAIN PATHOGENIC BACTERIA

1. The coelomic fluid of the earthworm Eisenia foetida Sav. always contains bacteria. 2. The numbers of bacteria which normally occur and the number of phagocytes have been estimated. 3. The phagocytosis rate of three species of bacteria, Aeromonas hydrophila, Yersinia ruckeri and Serratia marcescens has been measured in vitro. 4. These bacteria multiply in coelomic fluid devoid of coelomocytes in vitro, and in vivo when injected in sufficient concentration to overload the phagocytic capacity of the worm. 5. Repeated vaccination did not affect the phagocytosis rate. 6. Infection of the coelomic fluid can occur from the gut. 7. The results suggest that while the phagocytosis rate of the different bacteria tested differs, worms remain healthy by phagocytosis aided by bacteriostatic or bacteriocidal substances which may also have an opsonic role, but that reduction in the number of phagocytes, or introduction of excessive numbers of bacteria can lead to septicaemia and death. In the case of A. hydrophila and Y. ruckeri death may be caused also by exotoxins.