Bacterial associations with commercially important marine bivalves

This study is concerned with the interactions between bacteria and commercially important bivalves. It is divided into two sections, the first part consists of the isolation and identification of bacteria collected from hatcheries at Reculver, Guernsey and Conwy in the U.K. Identification of the bacteria was carried out using phenotypic analysis combined with numerical taxonomy. Results showed that diverse microbial flora was detected in these shellfish farms, and that the principal groups consisted of Vibrio, Enterobacter, Pseudomonas, Cytophaga, Flavobacterium, Moraxella, Micrococcus and Aeromonas species. The distribution of these bacteria was as follows; Vibrio were predominant at Guernsey whereas Enterobacter and Cytophaga were the most common isolates at Reculver and Conwy. Antibiotic resistance patterns were performed in order to establish the profile of bacterial resistance to commonly used aquaculture and medical important antibiotics. The outcome was a heterogenous resistance profile. Part two includes the analysis and screening of the tentatively identified bacterial isolates for their toxicity to bivalve haemocytes and known pathogens. In parallel other isolates from France, Spain, Norway and Scotland were included in the study for comparative analysis. Isolates were subjected to cytotoxicity tests in order to detect potential bivalve pathogens. A cytotoxocity test was developed and optimised for this purpose using natural conditions where possible. Alternative methods such as neutral red dye and molecular probes were used in order to obtain better results but were not successful. Thus visual observation of haemocyte-bacteria interactions proved to be more reliable. Principally bacteria from Vibrio and Cytophaga I Flavobacterium produced marked effects on haemocytes. Further tests revealed that this effect was more prominent in filtered haemolymph when compared to filtered sterile sea water. This was probably due to the presence of factor(s) that may have played an important role in this reaction, which merit further investigation to elucidate their exact role. Species specificity of several bacterial pathogens of bivalves is reflected in their interaction with bivalve haemocytes