Human Pathogenic Species Respond Distinctively to Lactic Acid Stress.

Several species are opportunistic human fungal pathogens and thrive in various environmental niches in and on the human body. In this study we focus on the conditions of the vaginal tract, which is acidic, hypoxic, glucose-deprived, and contains lactic acid. We quantitatively analyze the lactic acid tolerance in glucose-rich and glucose-deprived environment of five species: and . To characterize the phenotypic space, we analyzed 40-100 clinical isolates of each species. Each species had a very distinct response pattern to lactic acid stress and characteristic phenotypic variability. and were best to withstand high concentrations of lactic acid with glucose as carbon source. A glucose-deprived environment induced lactic acid stress tolerance in all species. With lactate as carbon source the growth rate of is even higher compared to glucose, whereas the other species grow slower. may use lactic acid as carbon source in the vaginal tract. Stress resistance variability was highest among strains. In conclusion, each spp. is adapted differently to cope with lactic acid stress and resistant to physiological concentrations.