Isolation and identification of heterotrophic and enteric bacteria from fresh and salted hilsa (Tenualosa ilisha)

Abstract

Hilsha (Tenualosa ilisha) is a popular, tasty fish found in the rivers of Bangladesh round the year. In our local market both fresh and salted hilsha are available. Samples were collected from different local markets of Dhaka city to investigate the microorganisms associated with fresh and salted hilsa fish. Along with the associated microorganisms nutritional quality was also studied. During this study four different market of Dhaka city viz. Palashi Bazaar, Karwan Bazaar, Anando Bazaar and New Market were selected for sampling.The temperature and pH of fresh fish samples ranged from 28.6 to 32.40C and 6.55 to 6.72 respectively while the temperature and pH of salted fish samples ranged from 28.2 to 32.5ºC and 5.31 to 5.70, respectively. Five types of bacteriological culture media viz. nutrient agar (a generalized complex medium), EMB agar medium for coliform, SS agar for Salmonella-Shigella, MSA agar for Staphylococcus and TCBS for Vibrio were used to assess the quantitative and qualitative study of bacteria associated with the hilsa fish. The bacterial load of fresh hilsa fish was ranged between 6.6×104 cfu/gm to 1.22 ×106 cfu/g, 1.5×102 to 6.35×103 cfu/g, 8.5×103 to 1.2×106 cfu/g and 2.5×102 to 1.64×105 on nutrient agar, SS agar, EMB agar and MSA agar respectively. On the other hand the bacterial load of salted fish samples was found to be ranged between 1.4×104 to 7.45×106 cfu/g, 6.4×103 to 7.75×104 cfu/g, 1.5×102 to 4×104 cfu/g on nutrient agar, EMB agar, and MSA agar, respectively. No bacterial colony was found on SS agar and TCBS agar plate in salted fish. The results clearly showed that fresh fish samples were associated with high bacterial loads than that of salted fish. The highest heterotrophic bacterial count 1.22×106 cfu/g recorded in the fresh fish sample of Karwan Bazar. Maximum coliform bacterial count was also noticed in the fresh fish sample of same market. During this investigation 66 bacterial colonies were isolated. Of them 24 bacterial isolates were selected for detail study. Out of 26 isolates 12 were Gram positive bacteria and 12 were Gram negative bacteria. Among the Gram positive 3 were rod shaped and two were spore former and members of the genus Bacillus. The non spore former bacterium was the member of Listeria monocytogenus. The provisionally identified Bacillus spp. were Bacillus megaterium and B. marinus. The remaining 9 Gram positive bacteria were the members of Planococcus citreus (1), Micrococcus variens (1), Micrococcus nishinomiyaensis (1), Staphylococcus lentus(1), Staphylococcus epidermidis (2) and Staphylococcus aureus (3). Twelve Gram negative bacterial isolates belonged to the member of Salmonella paratyphi (2), Salmonella spp. (2), Escherichia coli (1), Proteus morganii (3), Proteus vulgaris (2), Vibrio sp.(1) and Halobacterium (1). Proximate composition of raw Tenualosa ilisha in dorsal and ventral part was 55.47% and 46.03% moisture, 18.94% and 24.25% protein, 23.47% and 24.24% lipid and 1.64% and 2.92% ash, respectively. In salted T. ilisha, the proximate composition of dorsal and ventral part was 44.88% and 40.05% moisture, 20.79% and 20.19% protein, 15.89% and 20.83% lipid and 18.15 and 18.35% ash. It was found that the protein, lipid, moisture contents decreased and ash content increased after salting condition.