Abstract:

Survival of Salmonella in sterile seawater and freshwater microcosms without supplemental nutrition was studied at ambient (30 ± 2°C) and refrigerated temperature (5 ± 1°C). When inoculated at high initial concentration (log 7.5 CFU ml-1), Salmonella survived for up to 16 weeks and 24 weeks respectively in seawater and freshwater at ambient temperature. At low temperature, cells could survive for 48 weeks in seawater and 58 weeks in freshwater microcosms. Trials with low initial cell density (log 3.1 CFU ml-1) revealed that the die-off rate was faster and a maximum survival of 13 weeks was recorded at 5°C in both the microcosms. Although, the bacteria survived for 13 weeks without supplemental nutrition, metabolic injury was observed as revealed by their failure to grow on selective media. Phenotypic variations were also observed on colonies recovered after prolonged starvation. These results suggested that Salmonella could survive well in nutrient-free seawater and freshwater microcosms. Survival is better supported in freshwater than in seawater microcosms and that low temperature favours longer survival. Starvation induced morphological changes can have identification bias and the survival potential of Salmonella sp. could pose potential risk of contaminating the aquatic products not only from polluted waters but also in oligotrophic seawater if they gain entry into such water systems.

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Date 2003/09/01

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