The dynamics of microorganisms and their association with clam in fresh water ecosystem

Abstract

Clams are shelled marine or fresh water mullusks belonging to the class Bivalvia. They are invertebrates with shells divided into two pieces called valves. They are rich source of proteins and minerals especially calcium and are recommended in the diet of pregnant women and in protein deficient cases. They inhabit the bottom of fresh water bodies or slow running waters. Fresh water is one which contain less than 0.5 parts per thousand of dissolved salts or other impurities, and are found in fresh water lakes, swamps and some rivers. The deposition of litter, substrates and other faecal materials in water body results in a build-up of pathogenic microorganism (bacteria) in the water which gives high burden on the water inhabitants including clams. The concentration of the bacteria in the water body varies with the season. This research was therefore aimed at accessing the type and density of bacteria and fungi present in fresh water associated with clams, and to determine the effect of the microorganism on the nutritional value of clams over a period of ten months in a fresh water ecosystem. Samples for analysis were water from Itu river, labeled sample A, sample B was water used to rinse the clams, sample C was homogenized clam intestine while sample D was homogenized body of the clam. The microbial load was determined using serial dilution and plating methods. Characterization and identification of microbial isolates was done using different standard biochemical tests, to determine; colonial morphology, Gram staining reaction, spore stain, motility, sugar fermentation, production of indole, coagulase and catalase. The methods as outlined by Association of Official Analytical Chemistry were used for physicochemical and nutritional analysis to test for moisture content, ash content, crude protein, fibre, fats and mineral elements. Results of the various analysis showed that, the total microbial count for the four samples through the ten months sampling period was highest in February with sample C having the highest of 1.2 X 105 cfu/mL, followed by sample D 7.0 X 104 cfu / mL, sample B had 5.8 X 104 cfu / mL while sample A was the lowest with 4.4 X 104 cfu / mL. The count was lowest in the month of September with C having 3.7 X 104 cfu / mL, followed by D with 2.4 X 104 cfu / mL, B had 8.0 X 103 cfu / mL while A the lowest was 4.0 X 103 cfu / mL. Microorganisms present in the fresh water sample and clam were mostly coliform from faecal matter and include; Staphylococcus aureus, Enterobacter aerogenes, Spirosoma lingual, Bacillus cereus, Lactobacillus plantarum, Escherichia coli, Flavobacterium aquatile and Micrococcus varians. We conclude that microbial load was higher in dry season than in rainy season probably due to dilution of the water and its velocity during rainy season. Results also showed that the nutritional values of the clam varies with season and density of microbial load. We recommend proper sanitation in water where clams are harvested and proper boiling of clams and possible removal of the intestine before consumption especially during the dry season.