420. A Rapid PCR Assay Detects Fungemia Due to Mixed Candida Species That Is Missed by the Clinical Microbiology Laboratory

BACKGROUND: As identified by blood cultures, ~4% of candidemia is caused by mixed Candida spp. Studies of PCR-based diagnostics, however, suggest that ≥ 2 spp. can be detected in 6%–36% of candidemia. Our objective was to use molecular methods to determine rates of mixed Candida spp. fungemia at our center. 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 one patient, C. albicans and C. glabrata co-infection was identified. Using our PCR marker, threepatients (15%) were found to have mixed spp. infections, including the patient known to have C. albicans/C. glabrata co-infection. In one patient diagnosed originally with C. glabrata fungemia, C. albicans was also identified. In one patient diagnosed with C. parapsilosis fungemia, C. fabianii 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 C. parapsilosis and C. fabianii isolates from the co-infected patient revealed that colony morphologies were indistinguishable on solid agar at 48 hours. Thereafter, C. parapsilosis formed smaller wrinkled colonies, comprised of a mixture of elongated and round cell morphologies, whereas C. fabianii demonstrated round small cells, and formed smooth, big colonies. In addition, C. parapsilosis showed increased agar invasion and echinocandin resistance. C. fabianii 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. DISCLOSURES: All authors: No reported disclosures.