Sample inoculation. Aliquots of diluted bacterial cocktails
were spot inoculated on each red salsa sample container at five
locations for even distribution of inocula. Two inoculation levels,
low (3.2 log CFU/g) and high (4.2 log CFU/g), were used for the S.
aureus survival study. These two inoculation levels were designed
to simulate situations in which the food matrix was contaminated
because of mishandling. The log difference was used to evaluate
the effect of inoculation level on the ability of the bacterium to
overcome the environmental conditions and grow. For the toxin
production assay, a higher initial inoculation of 6.0 log CFU/g was
used to provide the population level necessary for toxin
production. For the Salmonella survival study, a single inoculation
level of 15 to 20 cells per sample was used. This low inoculation
level was selected based on information provided by the U.S. Food
and Drug Administration Web site (21), which indicates that
Salmonella has a very low infective dose.