Validation of predictive mathematical models describing growth of Staphylococcus aureus

Abstract

An investigation was performed on the growth of Staphylococcus aureus in a commerciallly available, sterile, homogeneous food at 12°C with 1.2 and 5.9% NaCl; at 25° C with 10.4% NaCl; and at 20 and 35°C with 1.2, 5.3 12.5, and 15.8% NaCl: over a pH range of 5.5 to 7.5. Growth data were filled to the Gompertz equation and the resulting growth kinetics were compared with predictions from the Pathogen Modeling Program (PMP) and Food MicorModel (FMM). For the PMP. predicted lag-phase durations varied from 0.5 to 130 h longer than the observed values. In general. close agreement with growth rates was obtained but there was a 10-fold difference in one case. For FMM, predicted lay-phase durations ranged from 27 h shorter to 47 h longer than the observed values. Again, close agreement with growth rates obtained, but in one case a fivefold difference was observed. In general, for the sterile foods used under the growth conditions tested, the models underestimated the growth of S. aureus. This implies that while the models can be used as a guide to indicate growth rates in foods they should not be relied upon as the sole determinant of the product's safety.