Persistence of Salmonella enterica Serovar Agona in Oil for Fish Feed Production

摘要

Globally, Salmonella is one of the most important food borne pathogens. Even though bacteria in the genus Salmonella are typical intestinal organisms, they show ability to survive and even multiply in environments other than the intestine, e.g., food and feed. Furthermore, the survival of Salmonella sp. in stored food and feeds are enhanced by a lowered water activity (aw). Some Salmonella serovars such as Agona, may occasionally be found in animal feed and its ingredients, as well as in the feed production facilities. In the present study we have examined the persistence of Salmonella enterica serovar Agona in an experimentally contaminated marine oil intended for fish feed production. The bacterium was added to the sterile oil in an average concentration of 2x106 Colony Forming Units (CFU mL-1) and kept aerobically at 20°C to mimic common storage conditions. At days 0, 6, 18, 32, 54, 80, 94, 116 and 122, one sample from each of ten parallel aliquots of the oil were examined quantitatively and qualitatively. At day six after inoculation, a log increase of viable Salmonella cells could be observed, as the average number reached 1.9x107. From day 18-54 the cell numbers were stable at between 1.8 and 3.1x106 cells. After day 54 until the termination of the experiment the number of cells steadily decreased and the bacterium could not be detected by quantitative or qualitative methods at day 122 after inoculation. This experiment demonstrates that Salmonella enterica serovar Agona can survive for at least four months in a marine fish oil.