Purpose: This work determines the survival of three serovars of Salmonella, either individually or as a cocktail, in water representative of surface waters.
Methods: Salmonella Newport, Anatum, and Gaminara (all previously isolated from surface waters), were prepared individually (n = 3) or in a cocktail (n = 6) and added to sterile deionized water (DI), sterile (SS) or non-sterile (NSS) surface water from the same local water source, or EPA worst case water (EPAWC). Uninoculated water was stored for 24 h prior to inoculation at incubation temperature. Incubation temperatures were 15, 21, and 28°C; samples were stored stationary and protected from light for up to 6 months. Samples were serial diluted in 0.1% peptone water, and spread plate onto XLT4 agar. Plates were incubated 24 ± 2 h at 37°C and colonies counted by hand. Once populations fell below the limit of detection by spread plating, MPN enrichments were performed.
Results: No significant difference existed between the individual serovar or cocktail populations at any time point. At time zero, no significant differences (P > 0.05) between Salmonella populations, 7.9 ± 0.1 log CFU/100 ml, existed between water types or temperatures. Populations in DI, SS, and EPAWC were either not significantly different or significantly different at only one time point. By day three, and thereafter, in NSS populations were significantly lower than those in other waters. At six months, populations in NSS significantly decreased to 2.7 ± 0.8, 3.8 ± 0.7, and 0.9 log MPN/100 ml, at 15°C, 21°C, and 28°C, respectively. In DI, SS and EPAWC, populations at 15°C and 21°C were significantly lower than waters at 28°C.
Significance: Salmonella may persist in various types of water for durations exceeding six months after initial contamination. Survival is higher in water without background populations.