Bacterial Profile of Black Clam (Villorita cyprinoides var. cochinensis) and Clam Harvesting Waters from Vembanad Lake in Kerala (India)

Abstract

The bacterial flora of black clam (Villorita cyprinoides var. cochinensis ) and water samples collected from three clam harvesting areas in Vembanad lake (Kerala, India) were studied. Samples were examined for total aerobic mesophilic count, psychrotrophic count. Vibrios and indicator bacteria. The mean mesophilic counts were in the range of 5.0-5.7 logu, cfu ml"1 and 5.6-6.4 log|0cfu g1 respectively for water and clam samples. The shellfish collected from Vembanad lake showed faecal contamination at levels which did not conform to legal standards. The densities of enterococci and Clostridium perfringens were higher in clams than in the growing waters indicating bioconcentration of these organisms in clams. The bacterial flora on newly caught clam consisted of a variety of bacteria of which 28% were Gram-positive and 72% were Gram-negative. Vibrio and Aeromonas together formed 46% of the total . mesophilic flora. Vibrio species isolated were V. fluvialis, V. fnrnissi, V. metsdmikovii. Among Aeromoms species, Aeromonas hydrophila, A. veronii biovar. sobria, A. media, A caviae were isolated. The remaining Gram-negative genera in the flora belonged to Acinetobacter, Shewvanella, Moraxella and Pseudomonas. The Gram-positive flora of clam was constituted by genera Bacillus, Micrococcus, Corynebacterium and Arthrobacter. High prevalence of Escherichia coli, faecal Streptococci and C. perfringens in water and clam indicates high degree of faecal pollution of the harvesting areas. The isolation of potentially pathogenic bacteria from clams indicates a risk for health of people consuming and also handling raw seafood