Emerging evidence for a multitude of mechanisms and factors that determine amphotericin B resistance in pathogenic fungi

The fungicidal polyene amphotericin B (AMB) is the oldest antifungal for the treatment of systemic infections, and it remains a critical broad-spectrum therapeutic option, despite its well-documented nephrotoxicity. In many countries use of conventional amphotericin deoxycholate has been eclipsed by the introduction in the 1990s of the considerably more expensive but much less nephrotoxic lipid formulations. Amphotericin B is valued for its strong fungicidal activity at low doses and its rarity of resistance, as resistance usually carries a significant fitness cost for fungi. However, emerging pathogens such as Candidozyma auris (formerly Candida auris) often exhibit significant resistance levels, with >30 % of clinical isolates showing reduced AMB susceptibility. Like azoles, AMB targets ergosterol in the fungal membrane, but unlike azoles, it binds pre-existing ergosterol; however, reduced ergosterol alone does not fully explain emerging resistance. Recent studies have revealed novel, often sterol-independent mechanisms related to sphingolipid content that drive AMB resistance, particularly in yeast species. These findings broaden our understanding and emphasize critical knowledge gaps. We review these evolving mechanisms and the pressing need for further research into the evolution of AMB resistance pathways.