Mechanism of the temperature protective effect of salts on Staphylococcus aureus

Abstract

The maximum temperature for growth of S. aureus was about 2.degree. C higher in media supplemented with NaCl. MgCl2 was the most effective protectant at 0.4 M. NaCl and KCl were as effective as MgCl2 when tested at 1 M. NH4Cl was less effective at all concentrations and LiCl was not protective. Sucrose and glucose (1 M) gave about half the biomass of 1 M NaCl. Glycerol, Na2SO4, NaNO2, NaNO3 and CH3COONa were not protective. Protection is probably due to the nonpenetrating solute (sucrose) or the nonpenetrating Cl- anion. Mg2+ had an effect additional to that attributable to Cl- because MgSO4 and to a slight extent (CH3COO)2Mg were protective. The morphology of the cells grown at 45.degree. C in 1 M NaCl was abnormal: septation became irregular, cell walls were thickened and the cells occurred in irregularly-sized clumps surrounded by capsular material. [This study has relevance to production of toxin in foods.].