Isolation and Characterization of Shewanella putrefaciens from Farm Reared Freshwater Prawn and Farm Environment

Farmed Macrobrachium rosenbergii, farm water and mud were analysed for hydrogen sulphide producing bacteria including Shewanella putrefaciens. The biochemical characteristics and spoilage potential of S. putrefaciens strains isolated from M. rosenbergii were investigated and compared to marine and brackishwater strains isolated from fish (Rastrelliger kanagurta) and black clam(Villorita cyprinoides) respectively. The H2S producing bacteria including S. putrefaciens constituted a low proportion (<2%) of the total aerobic flora of pond water and mud and 12% of the total aerobic population on fresh prawn. On icing, there was a lag or slight decrease in the counts of H2S producing bacteria including S. putrefaciens in the muscle of M. rosenbergii. The proliferation started on 16th day of iced storage and the count of sulphide producers reached ca. 6.25 log (10) cfu g (-)1 in prawn muscle at the time of rejection after 3 weeks. Gram-negative, non-fermentative, motile rods constituted 16-25% of the hydrogen sulphide producing bacteria on prawn muscle and intestine and they were identified as Shewanella putrefaciens. The results indicate that S. putrefaciens is an important spoiler of freshwater prawn. All the S. putrefaciens isolates from M rosenbergii were able to produce H2S and reduce TMAO and exhibited high spoilage potential. The present study suggests that counts of H2S producing bacteria can be a useful indicator of quality deterioration of farm reared M. rosenbergii.