Influence of copper on resistance of Lumbricus terrestris to bacterial challenge

Earthworms of the species Lumbricus terrestris were challenged orally and intracoelomically with two bacterial species, Aeromonas hydrophila and Pseudomonas aeruginosa, and mortality rates were observed. Neither A. hydrophila nor P. aeruginosa were found to be particularly pathogenic for L. terrestris at injected doses of up to 108 colony forming units per earthworm using either route of exposure. The influence of Cu++ (as CuSO₄) on the earthworm's response to bacterial challenge was investigated by exposing L. terrestris to sublethal levels of Cu++ prior to bacterial challenge. Exposure to Cu++ at sublethal concentrations of 1, 2 and 3 μg Cu ++/cm2 for 120-h prior to bacterial infection with A. hydrophila or P. aeruginosa did not have a pronounced influence on the host resistance to challenge as measured by earthworm mortality. Measurement of effects of copper on the earthworm's ability to agglutinate rabbit erythrocytes demonstrated significantly greater agglutination titers indicating that Cu++ exposure caused coelomocyte death, autolysis and release of cell lysates including agglutinins into the coelomic cavity. This may explain the resistance to bacterial challenge demonstrated in this research.