Insight into Virulence and Mechanisms of Amphotericin B Resistance in the Candida haemulonii Complex

The Candida haemulonii complex includes emerging opportunistic human fungal pathogens with documented multidrug-resistance profiles. It comprises Candida haemulonii sensu stricto, Candida haemulonii var. vulnera, Candida duobushaemulonii, Candida pseudohaemulonii, and Candida vulturna. In recent years, rates of clinical isolation of strains from this complex have increased in multiple countries, including China, Malaysia, and Brazil. Biofilm formation, hydrolytic enzymes, surface interaction properties, phenotype switching and cell aggregation abilities, extracellular vesicles production, stress response, and immune evasion help these fungi to infect the host and exert pathological effects. Multidrug resistance profiles also enhance the threat they pose; they exhibit low susceptibility to echinocandins and azoles and an intrinsic resistance to amphotericin B (AMB), the first fungal-specific antibiotic. AMB is commonly employed in antifungal treatments, and it acts via several known mechanisms. Given the propensity of clinical Candida species to initiate bloodstream infections, clarifying how C. haemulonii resists AMB is of critical clinical importance. This review outlines our present understanding of the C. haemulonii complex's virulence factors, the mechanisms of action of AMB, and the mechanisms underlying AMB resistance.