High-frequency, in vitro reversible switching of Candida lusitaniae clinical isolates from amphotericin B susceptibility to resistance

Recent studies have revealed an increase in the incidence of serious infect ions caused by non-albicans Candida species. Candida lusitaniae is of speci al interest because of its sporadic resistance to amphotericin B (AmB). The present in vitro study demonstrated that, unlike other Candida species, C. lusitaniae isolates frequently generated AmB-resistant lineages form previ ously susceptible colonies. Cells switching from a resistant colony to a su sceptible phenotype were also detected after treatment with either UV light , heat shock, or exposure to whole blood, all of which increased the freque ncy of switching. In some C, lusitaniae lineages, after a cell switched to a resistant phenotype, the resistant phenotype was stable; in other lineage s, colonies were composed primarily of AmB-susceptible cells. Although resi stant and susceptible lineages were identical in many aspects, their cellul ar morphologies were dramatically different, Switching mechanisms that invo lve exposure to antifungals may have an impact on antifungal therapeutic st rategies as well as on standardized susceptibility testing of clinical yeas t specimens.