In Vitro Acid Resistance of Feline-Derived Candidozyma auris Isolates in Simulated Gastric Fluid: A Pilot Study

The survival of Candidozyma (Candida) auris under gastric conditions remains poorly understood, particularly in veterinary species. This pilot in vitro study evaluated the resistance of two cat-derived C. auris strains and Candida parapsilosis ATCC 22019 in simulated gastric fluid (SGF). Yeast suspensions were exposed to SGF adjusted to pH 1–5 and 7 for up to 4 h at 37 °C, and colony-forming units (CFUs) were enumerated at 1, 2, and 4 h. Results were expressed as mean log10 CFU/mL ± standard deviation. A clear pH-dependent effect was observed: At pH 7, all strains showed increased CFU counts over time, whereas acidic conditions induced a marked reduction in culturability. At pH 1, reductions of approximately 3–4 log10 units occurred within 1 h, while at pH 2–5 a more moderate decrease of about 1 log10 unit was observed, with most reduction occurring early and stabilizing over time. Two-way ANOVA confirmed significant effects of pH and exposure time, with a significant interaction for all strains (p < 0.0001). Overall, gastric-like acidity strongly reduced, but did not completely abolish, the culturability of the two feline C. auris isolates under the specific in vitro conditions tested. Further studies using larger isolate collections and more physiologically relevant gastrointestinal models are needed to determine whether these findings translate into in vivo survival, intestinal transit, or colonization.