Cell Wall Changes in Amphotericin B-Resistant Strains from Candida tropicalis and Relationship with the Immune Responses Elicited by the Host

Abstract

eWe have morphologically characterized Candida tropicalis isolates resistant to amphotericin B (AmB). These isolates present an enlarged cell wall compared to isolates of regular susceptibility. This correlated with higher levels of ␤-1,3-glucan in the cell wall but not with detectable changes in chitin content. In line with this, AmB-resistant strains showed reduced susceptibility to Congo red. Moreover, mitogen-activated protein kinases (MAPKs) involved in cell integrity were already activated during regular growth in these strains. Finally, we investigated the response elicited by human blood cells and found that AmB-resistant strains induced a stronger proinflammatory response than susceptible strains. In agreement, AmB-resistant strains also induced stronger melanization of Galleria mellonella larvae, indicating that the effect of alterations of the cell wall on the immune response is conserved in different types of hosts. Our results suggest that resistance to AmB is associated with pleiotropic mechanisms that might have important consequences, not only for the efficacy of the treatment but also for the immune response elicited by the host.A mphotericin B (AmB) is a widely used antifungal drug that presents strong killing activity against fungi after binding to ergosterol. Classically, it has been described that AmB induced cell death by forming pores at the level of the cell membrane (1, 2). However, recent findings suggest that AmB elicits its fungicidal effect through multiple mechanisms. In this sense, AmB induces ergosterol sequestration, which causes alterations in the cell membrane that result in killing of the cells (3, 4). In addition, AmB induces a significant accumulation of reactive oxygen species (ROS), which has been correlated with cell damage, apoptosis induction, and death (5-9).Resistance to AmB is a complex process, and multiple mechanisms have been described to be responsible for it. Lack of ergosterol at the cell membrane has been frequently correlated with reduced susceptibility to AmB (10-14). However, there are also some cases in which resistance to AmB can occur in cells with normal ergosterol content (15, 16). Aspergillus terreus, which is a mold that presents reduced susceptibility to AmB, contains similar ergosterol content to Aspergillus fumigatus, which is fully susceptible to this antifungal. In this case, increase in catalase and reduction of ROS production have been associated with increased resistance to AmB (17). Moreover, mechanisms that protect against the production of ROS also confer reduced susceptibility to AmB (6, 9). These results indicate that AmB exerts multiple responses in the cells and that resistance to this antifungal can be acquired by different mechanisms.The correlation between the cell wall and resistance to AmB has been poorly described. A relationship between resistance to AmB and changes in the cell wall has been observed in different fungi (18)(19)(20), although it is not known to what extent changes in the cell wall contribute to amphotericin B res...

Generational distribution of a Candida glabrata population: Resilient old cells prevail, while younger cells dominate in the vulnerable host

“…The observation that glucan is much more abundant in old cells compared to young cells is supported by recent studies in Candida tropicalis , where a thicker cell wall rendered strains less susceptible to amphotericin B and more resistant to stress responses [66]. Also in this instance, the authors found more beta-glucans in strains with thicker cell wall with no change in chitin content, similar to our findings.…”

Efficacy of chemical disinfectants for the containment of the salamander chytrid fungus Batrachochytrium salamandrivorans

“…In these latter, cell wall composition (mainly elevated levels of β-1,3 glucan), wall thickness, and relative porosity are linked to antifungal susceptibility (see e.g. [23, 29]). Chytrid zoospores are surrounded by a plasma membrane, but whenever a zoospore ‘settles’, or retracts its flagellum and encysts, a cell wall is formed which increases in size and thickness to become a sporangium [20,30].…”

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