Microbial pollution of sea water and shellfish in Morocco
1997
Bouchriti, N. | Marrakchi, A.E. | Goyal, S.M.
Microbiological contamination of a Morocco oyster growing area was determined on the basis of bacterial analyses. A taxonomic study involving 215 strains of faecal streptococci revealed the existence of three species, Streptococcus faecalis, S. faecium and S. bovis. This taxonomic study allowed the determination of the sources of pollution which are manure, recreational activity, installation of spats and traditional fishing activity. The changes in the bacteria levels of mussels from harvest to sale were also studied. Freshly harvested and market mussels were the most contaminated while shucked mussels, obtained by heating shellstock were the least contaminated. Heating, used as a means of removing shells, reduces the initial bacterial loads. However storage of mussels prior to marketing resulted in their recontamination. A number of 803 strains of Vibrio isolated from sea water, shellfish and sediments were identified. The most predominant species was V. alginolyticus (62.4%), followed by V. fluvialis (12.1%), V. anguillarum (11.5%) and V. harvevi (9.6%). The frequency of occurence of V. parahaemolyticus and V. vulnificus, which are human pathogens, was low, 2.2% and 0.4%, respectively. Shellfish harvested from some Moroccan coastal areas contained high levels of faecal bacteria. It is advisable therefore, to depurate them before marketing and to place some control on recreational activities in the vicinity of shellfish growing areas. A strict surveillance should prevent clandestine harvesting and selling of mussels. Three methods were compared for the concentration of poliovirus from artificially contaminated oysters (Crassostrea gigas), mussels (Mytilus edulis), and carpet-shell clams (Ruditapes decussatus) grown in Morocco. For all shellfish species tested, the adsorption-elution-precipitation method gave the lowest virus recovery (27.2%), whereas the two elution-precipitation methods yielded average virus recoveries of 42%. For oysters, none of the tested methods gave satisfactory viral recovery while for mussels and clams it is possible to use the two elution-precipitation methods. It is advisable to develop a superior method for the concentration of viruses from oysters. Before using a particular method in the field, the efficiency of the method should be evaluated using known amounts of virus.
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