Filamentous growth and elevated vaginopathic potential of a nongerminative variant of Candida albicans expressing low virulence in systemic infection

Abstract

The vaginopathic potential and the intravaginal morphology of a nongerminative variant of Candida albicans, strain CA-2, were studied in a rat vaginitis model. Although it expressed low virulence in systemic infections, strain CA-2 was capable of causing a vaginal infection of the same duration and extent as that obtained in rats challenged with the germ- tube-forming strain C. albicans 3153 from the stock collection or with a fresh clinical isolate of C. albicans from a case of human vaginitis. During the experimental infection, the CA-2 cells did not maintain their yeast morphology but gave rise to single enlarged-elongated elements (1 to 2 days) which grew predominantly as coarse, short, pseudomycelium-like filaments (2 to 3 days) and then as long threads (7 days). These latter filaments were ultimately indistinguishable from the hyphal filaments formed by the germ- tube-forming strains, which, however, initially developed in the vagina by typical germ tube formation. This peculiar morphological development of strain CA-2 was not observed in organs of systemically infected mice, where, in contrast to strain 3153 which formed typical hyphae, strain CA-2 maintained a typical pattern of yeast growth. Vaginal isolates of strain CA- 2 taken at different days of infection were found to be identical to the challenging CA-2 cells, in terms of biochemical characteristics, inability to form germ tubes in any medium at 37°C in vitro, echinocandin resistance, DNA biotype, and low virulence in systemic infections in mice. Thus, experimental vaginitis by strain CA-2 is associated with a peculiar filamentous growth in the vagina, through an apparently novel morphological development bypassing classical germ tube formation but ultimately leading to ordinary hyphae. The elevated vaginopathic potential of strain CA-2, in contrast to its low virulence in systemic infection, also suggests that different Candida virulence factors (and host responses) come into play in local and disseminated candidal infections.