Model for combined effect of temperature and salt concentration/water activity on the growth rate of Staphylococcus xylosus

The combined effect of temperature and NaCl concentration/water activity on the growth rate of a strain of halotolerant Staphylococcus is described by the squareroot models which had been used previously to model temperature dependence only. The model r = b ( T ‐ T min ) is shown to be a special case of the BélehraAdek temperature function which is given by r = a ( T ‐ aL) d . The constant aL is the so‐called ‘biological zero’ and equivalent to T min in the square‐root models. This and the exponent d = 2 were unaffected by changing NaCl concentration/water activity. The Bélehradek‐type equations are preferable to the Arrhenius equation in that their parameters do not change with temperature. The constancy of T min allows derivation of a simple expression relating growth rate of strain CM21/3 to temperature and salt concentration/water activity within the range of linear response to temperature predicted by the square‐root model.