Serum bactericidal activity in the horseshoe crab, Limulus polyphemus.

Serum from the horseshoe crab, Limulus polyphemus, was examined for bactericidal activity against five species of bacteria. Greatest activity was found against Pseudomonas putida and Flavobacterium sp.; with the former, serum dilutions as high as 1:20 were capable of reducing viable counts by 50% within 2 h. Bactericidal activity of a significantly lesser magnitude was demonstrated against Serratia marcesencs and Salmonella minnesota. No killing was seen when the lobster pathogen Aerococcus viridans (formerly Gaffkya homari) was used. The cidal activity against Flavobacterium sp. remained relatively consistent for 6 months.