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Appl Environ Microbiol. 1974 March; 27(3): 443-447
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Interaction of pH and NaCl on Enumeration of Heat-Stressed Staphylococcus aureus¹

Department of Microbiology and Medical Technology, The University of Arizona, Tucson, Arizona 85721
Department of Dairy and Food Sciences, The University of Arizona, Tucson, Arizona 85721

ABSTRACT

The effect of pH level and NaCl concentrations, alone and in combination, on the enumeration of unstressed and heat-stressed cells of three strains of Staphylococcus aureus was determined. A definite narrowing of the optimum pH range for enumeration of both unstressed and heat-stressed cells was observed as the NaCl concentration was increased from 0.0 to 7.5%. Counts of unstressed cells diminished only slightly with increases in NaCl, whereas heat-stressed cells showed a marked sensitivity to NaCl concentrations of 4% and above, regardless of the pH level. Because of this sensitivity to NaCl, recoveries were far poorer than with unstressed cells at NaCl concentrations of 4% and above.

² Present address: Presbyterian Hospital, Albuquerque, N.M. 87106.

¹ Arizona Agricultural Experiment Station technical paper no. 2193.