MODEL FOR THE SURVIVAL OF STAPHYLOCOCCUS-AUREUS IN NONGROWTH ENVIRONMENTS

A model was developed to estimate the survival times of Staphylococcus aureus in nongrowth environments. A four strain mixture of S. aureus was inoculated into BHI broth that had a lactate buffer with various c ombinations of pH (3-7) and lactate (0-1%), NaCl (0.5-20%) and NaNO2 ( 0-200 ppm) and stored at different temperatures (4-42 degrees C). At a ppropriate times the survivors were enumerated by sampling and spreadi ng on TSA plates. The survival curves were modeled with two forms of a logistic equation and the D values were determined. Polynomial regres sion equations were then calculated to predict the effect of the envir onmental factors on the D values. Survival times were increased with h igher pH values, lower temperatures, and lower nitrite and lactate con centrations. Added salt increased survival times until the salt concen trations exceeded that of most foods.