Plating medium pH as a factor in apparent survival of sublethally stressed yeasts.

Sublethally stressed cells of 9 of 10 species of yeast were recovered at maximum levels when potato dextrose agar was adjusted to approximately pH 8. The optimum for candida utilis was at approximately pH 10. At pH 3.5, as commonly employed with media selective for yeasts and molds, recovery of heat-stressed organisms ranged from essentially the same as at optimum pH to levels of 1% or less of the maximum count. The extent to which this may be of practical significance in assessing the microbiological quality of food products remains to be determined.