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Bacterial infection in the Dungeness crab, Cancer magister

16 November 2010


The health of the marine environment is deteriorating, and coastal regions are showing increasing signs of pollution and bacteria. Our previous work showed that the Dungeness crab maintains low levels of a Psychrobacter strain in the hemolymph. In the current study we determined the presence of bacteria in the hemolymph from 75 crabs sampled during the summer months of 2010. The level of infection and the strain of bacteria present were identified. Bacteria were isolated from the majority of crabs sampled (68 to 84%). The infection level was assessed by plate counting method and varied between: 0-28760 CFU/ml. The identity of the isolates was determined from 16S rDNA sequence. Psychrobacter was the most prevalent strain, although we obtained 7 other isolates by traditional culturing methods (tryptic soy agar with 2.5% NaCl and marine agar), and the presence of an unculturable strain was shown by molecular methods. In order to test effects of bacteria in the hemolymph, crabs were injected with buffered saline (control) or buffered saline with isolated Psychrobacter or Bacillus YT0027 (2.5 X 104 g-1 body weight), hemolymph samples were taken before injection and 80 min afterward. Hemolymph cell activity was estimated by mitochondrial enzyme activity using Cell Proliferation Reagent WST-1. Total hemolymph cell activity decreased after injection of bacteria. These data demonstrate that the chronic presence of a variety of bacteria in the hemolymph is common in the Dungeness crab and may present a constant challenge for their immune system.


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