The effect of temperature and water activity on the growth of Staphylococcus aureus

Abstract

The growth responses of Staphylococcus aureus 2064 as affected by water activity and incubation temperature were studied in two different laboratory media. Growth parameters at temperatures from 7 to 51°C and a<sub>w</sub> in the range from 1.0 to 0.86 were fitted using Ratkowsky models. The effect of temperature within its whole range on the specific growth rate was modelled by the extended model under the following equation: √µ = 0.0456 (T – T<sub>min</sub>) [1 – e<sup>0.447(T – T<sub>max</sub>)</sup>]. The water activity values of tested media were adjusted by sodium chloride in the range from a<sub>w</sub> = 1.0 to 0.86 and experiments were conducted at 15 and 18°C. The growth responses of S. aureus on water activity at 15°C and 18°C in PCA broth and BHI broth was described by simplified Ratkowsky model in the form: √µ = b × a<sub>w</sub>. Validation of the found relationships confirmed sound fitting of the data and thus the referred results of the isolate originated from ewes’ cheese can be used in the growth prediction of S. aureus, reliably.