In vitro synergistic activity of betulinic acid combined with azoles against pathogenic fungi.

BACKGROUND

Invasive fungal infections and emerging antifungal resistance threaten global public health, demanding effective combination therapies.

OBJECTIVE

To evaluate in vitro synergistic antifungal activity of betulinic acid (BA) combined with four azoles (itraconazole [ITR], voriconazole [VOR], posaconazole [POS], fluconazole [FLC]) against Aspergillus spp., Candida spp., Exophiala dermatitidis, and Cryptococcus neoformans.

METHODS

Per CLSI M27-A3/M38-A2, broth microdilution checkerboard assay determined BA's minimum inhibitory concentration (MIC) and synergy with azoles (n = 110); flow cytometry measured intracellular reactive oxygen species (ROS) in fungi co-cultured with BA.

RESULTS

BA alone had no antifungal activity, but showed synergy with specific azoles: BA/POS had 82.7% (43/52) synergy against Aspergillus spp., 95.2% (20/21) against E. dermatitidis, and 70% (7/10) against Candida auris (of 28 Candida spp., 28.6% synergy). BA/FLC had 55.6% (5/9) synergy against C. neoformans. Among the 110 strains, the synergy rates of BA with POS, ITR and VOR were 66.4, 10.9 and 2.7%, respectively; the BA-FLC synergy rate was 18.5% in 27 strains. BA/POS co-culture increased fungal ROS.

CONCLUSION

BA-POS reduces POS's MIC and exerts potent synergy against Aspergillus spp. and E. dermatitidis. BA has potential as an adjuvant for treating Aspergillus and E. dermatitidis infections.