Evaluation of the effect of pH on in vitro growth of Malassezia pachydermatis.

The purpose of this study was to evaluate the effects of pH on the growth of canine Malassezia pachydermatis isolates in vitro. Yeast growth was monitored by measuring the optical density with a spectrophotometer. The growth of American Type Culture Collection and field strains of M. pachydermatis was optimal between the pH values of 4.0 and 8.0, and inhibited at the ranges of 1.0 to 3.0 and 9.0 to 10.0. An analysis of covariance showed no significant differences among the growth curves at pH levels 5.0 to 8.0. Although specific contrast tests showed that the growth slope at pH 4.0 was significantly different from that at pH 5.0 to 8.0, only small, random differences were found when the growth slope at pH 4.0 was compared to the individual slopes at pH 5.0, 6.0, 7.0, and 8.0. The findings of this study suggest that topical acidifying products could be beneficial therapeutic options for cutaneous yeast infections in dogs.