Assessment of pH ranges for intestinal yeast growth at various cultivation temperatures

Prokopiev V.V.

Ltd. Clinical-diagnostic laboratory “Zdorovie”, Barnaul, Russia
Altai State Medical University, Barnaul, Russia

Aim. To evaluate the pH ranges supporting the growth of basidiomycetous (Rhodotorula mucilaginosa, Trichosporon spp.) and ascomycetous (Candida albicans, Geotrichum candidum, Pichia spp., Wickerhamiella pararugosa) yeasts at three incubation temperatures (25, 35, and 42°C).

Materials and Methods. The strains used in this study were isolated from fecal samples of patients at a multidisciplinary medical center during bacteriological examination. Fungal identification was performed using a Microflex mass spectrometer. To assess physiological pH ranges, the fungi were inoculated into microplates containing Sabouraud medium adjusted to pH values ranging from 2 to 11. Microbial growth at different pH levels was evaluated by measuring the difference in optical density (ΔOD) at 450 nm after 96 hours of incubation compared to the initial post-inoculation readings. Viability of the fungi at extreme pH values was confirmed by subculturing onto Sabouraud agar after 96 hours of incubation and by trypan blue staining.

Results. Significant differences in physiological pH ranges were observed among the studied fungal species. Cultivation temperature strongly influenced the pH ranges supporting microbial growth. Candida albicans and Pichia kudriavzevii demonstrated the ability to grow across the entire tested pH range (2-11) at all incubation temperatures.

Conclusions. Determining the pH ranges helps assess the potential of the studied fungi to cause infections in different human biotopes with varying pH levels and provides insights into the pathogenesis of mycoses caused by these microorganisms. The obtained data may also be useful for ecological and biotechnological evaluations of the studied yeasts.