Methods: We devised a rapid, PCR assay that identifies Candida spp. by amplifying ACT1 and accounting for differences in intron sizes. We extracted total DNA from blood culture bottles from 15 patients, from which Candida had been recovered by the clinical microbiology laboratory.
Results: Using standard laboratory protocols and MALDI-TOF, candidemia was ascribed to a single Candida sp. in 14 patients. In 1 patient, C. albicans and C. glabrata (Ca/Cg) co-infection was identified. Using our PCR marker, 3 patients (15%) were found to have mixed spp. infections, including the patient known to have Ca/Cg co-infection. In one patient diagnosed originally with Cg fungemia, Ca was also identified. In one patient diagnosed with C. parapsilosis (Cp) fungemia, C. fabianii (Cf) was also identified. In the latter two cases, analysis of colonies recovered from subculturing of blood culture bottles subsequently confirmed the presence of both spp. Comparative phenotypic studies of Cp and Cf isolates from the co-infected patient revealed that colony morphologies were indistinguishable on solid agar at 48 hours. Thereafter, Cp formed smaller wrinkled colonies, comprised of a mixture of elongated and round cell morphologies, whereas Cf demonstrated round small cells, and formed smooth, big colonies. In addition, Cp showed increased agar invasion and echinocandin resistance. Cf had increased growth rate, biofilm formation and resistance to neutrophil killing.
Conclusion: Mixed Candida spp. may account for more cases of fungemia than currently recognized by clinical laboratories. In some cases, failure to detect mixed spp. infections can have important clinical implications, including failure to appreciate antifungal resistance. It is possible that complementary phenotypic or virulence characteristics between isolates of different spp. may potentiate pathogenesis. More efficient methods of screening for mixed Candida spp. infections are needed for clinical laboratories.
C. J. Clancy,
M. H. Nguyen, None