Shell disease syndrome in the edible crab, Cancer pagurus – isolation, characterization and pathogenicity of chitinolytic bacteria

Abstract

Chitinolytic bacteria are believed to be the primary aetiological agents of shell disease syndrome in marine crustaceans. The disease principally results from the breakdown of their chitinous exoskeletons by the shell disease pathogens, but pathogenicity may also manifest internally should a breach of the carapace occur. The current study looks at the pathogenicity of a number of bacteria (predominantly from the genus Vibrio) isolated from the edible crab, Cancer pagurus. All chitinase-producing bacteria investigated were capable of growth in a minimal medium consisting of chitin powder from crab shells, but differed in their speed of growth and nature of chitinolytic activity, suggesting that they have different roles within the lesion community. Two isolates (designated I4 and I7) were chosen for studies on internal pathogenicity, which included the effect of the pathogen on crab tissues, the ability of the host to remove the bacteria from circulation and the antibacterial activity of crab blood. Initially, I4 was rapidly removed from circulation, but began to reappear in the blood after 24 h. By 100 h, 100 % of crabs were moribund. The septicaemic effects of the isolate were reflected in the low levels of its killing by blood-cell lysate and serum. By contrast, I7 was only slowly removed from circulation and caused the rapid mortality of all crabs in T 3 h. A large decline in the number of circulating blood cells following injection of I7 was mirrored by an accumulation of these cells in the gills. Initial experiments suggest that the death of the crabs following injection with I7 may be caused by toxic extracellular bacterial products that exert their effects on the blood cells and nervous system of the crabs.

Shell disease in Crangon crangon (Linnaeus, 1758): The interaction of temperature and stress response

“…It was previously described that the bacterial counts in the hemolymph are increasing with the severity of the disease, possibly resulting from a reduced ability of the host to clear the pathogens in their plasma (Homerding et al, 2012;Vogan et al, 2002). The hemocytes recognize and remove these foreign matters which become trapped in the gills, what might result in a decline in the respiration (Martin et al, 2000;Smith and Ratcliffe, 1980;White and Ratcliffe, 1982).…”

Shellfish as reservoirs of bacterial pathogens

“…They can not only cause infection of the crab shells, but also septicemic infection or death from extracellular bacterial products, terminating with death [23].…”

Identification and expression analysis of cDNA encoding chitinase-like protein (CLP) gene in Japanese scallop Mizuhopecten yessoensis

“…Chitin, composed of β(1,4)-linked N-acetyl-D-glucosamine residues, is a naturally occurring polysaccharide found in many life forms, including the exoskeleton and gut linings of insects, cell walls of microorganisms, microfilarial sheaths of parasitic nematodes, and shells of crustaceans (Fuhrman and Piessens, 1985;Kneipp et al, 1998;Vogan et al, 2002;Wills-Karp and Karp, 2004;Lee et al, 2008). The glycoside hydrolase family 18 (GH18), characterized by the ability to hydrolyze chitin enzymatically, has been identified in organisms that synthesize or metabolize chitin, such as insects, yeasts, and crustaceans, and those that do not synthesize or metabolize chitin, such as higher plants and mammals.…”