EFFECTS OF INCUBATION TEMPERATURE ON THE SALT TOLERANCE OF SALMONELLA

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Abstract
Salt has been shown effective in preventing growth of salmonellae in foods. Many of the studies reported in the literature have been on the lethal action of high levels of salt as used in curing brines. Little information is available on the interaction of incubation temperature and low levels of salt on the growth of salmonellae. The growth of Salmonella heidelberg, Salmonella typhimurium, and Salmonella derby in nutrient broth containing 0 to 8% added NaCl (in 0.5 or 1% increments) has been tested by shake cultures at 8, 12, 22, and 37 C. In addition, S. heidelberg has also been tested in 0 to 9% added NaCl at 39, 41, 43, and 45 C. At 8 C, growth of S. heidelberg took place in 1 and 2% added NaCl; S. typhimurium increased in numbers in 1% added NaCl; and S. derby failed to increase. When incubated at 12 C, the three serotypes were all able to increase in numbers in the range of 0 to 4% NaCl. At 22 C, this range increased from 0 to a maximum of 5 to 8%. When incubated at 37 C, the organisms were able to increase in numbers in up to 7 to 8% NaCl. The salinity of the medium was not found to increase the maximum growth temperature of S. heidelberg as has been reported in the literature for other organisms. Low levels of salt were found to stimulate growth of salmonellae. This stimulation was more pronounced at low temperatures than near the optimum for the organisms. Since salt is used to preserve foods, these data are important in the preservation of perishable foods. Salt concentrations preventing growth of salmonellae at low temperatures may not be sufficient to prevent growth of these pathogens at higher temperatures.

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