Epidemiology, antifungal susceptibility, and pathogenicity of Candida africana isolates from the United Kingdom

Abstract

Candida africana was previously proposed as a new species within the Candida albicans species complex, together with C. albicans and C. dubliniensis, although further phylogenetic analyses better support its status as an unusual variant within C. albicans. Here we show that C. africana can be distinguished from C. albicans and C. dubliniensis by pyrosequencing of a short region of ITS2, and we have evaluated its occurrence in clinical samples by pyrosequencing all presumptive isolates of C. albicans submitted to the Mycology Reference Laboratory over a 9-month period. The C. albicans complex constituted 826/1,839 (44.9%) of yeast isolates received over the study period and included 783 isolates of C. albicans, 28 isolates of C. dubliniensis, and 15 isolates of C. africana. In agreement with previous reports, C. africana was isolated exclusively from genital specimens, in women in the 18-to-35-year age group. Indeed, C. africana constituted 15/251 (6%) of "C. albicans" isolates from female genital specimens during the study period. C. africana isolates were germ tube positive, grew significantly more slowly than C. albicans and C. dubliniensis on conventional mycological media, could be distinguished from the other members of the C. albicans complex by appearance on chromogenic agar, and were incapable of forming chlamydospores. Here we present the detailed evaluation of epidemiological, phenotypic, and clinical features and antifungal susceptibility profiles of United Kingdom isolates of C. africana. Furthermore, we demonstrate that C. africana is significantly less pathogenic than C. albicans and C. dubliniensis in the Galleria mellonella insect systemic infection model.

Fig 1

Appearance of C. albicans (left panel) and C. africana (right panel) after 48 h of incubation at 35°C on CHROMagar.

Fig 2

Virulence of C. albicans, C. dubliniensis, and C. africana in Galleria mellonella larvae is species specific and temperature dependent. Kaplan-Meier plots of G. mellonella survival after injection with 10⁶ CFU/larva of C. albicans (solid lines), C. dubliniensis (dashed lines), or C. africana (dotted lines) or an equivalent volume of sterile PBS (arrowed lines) and incubation at 30°C (left panel), 37°C (middle panel), and 42°C (right panel). Four strains were tested per species, with 15 larvae per strain (60 larvae per species). Experiments were performed in duplicate; curves represent the combined (additive) data from all strains and all experiments.