In vitro C3 deposition on Cryptococcus capsule occurs via multiple complement activation pathways.

Complement can be activated via three pathways: classical, alternative, and lectin. Cryptococcus gattii and Cryptococcus neoformans are closely related fungal pathogens possessing a polysaccharide capsule composed mainly of glucuronoxylomannan (GXM), which serves as a site for complement activation and deposition of complement components. We determined C3 deposition on Cryptococcus spp. by flow cytometry and confocal microscopy after incubation with serum from C57BL/6J mice as well as mice deficient in complement components C4, C3, factor B, and mannose binding lectin (MBL). C. gattii and C. neoformans activate complement in EGTA-treated serum indicating that they can activate the alternative pathway. However, complement activation was seen with factor B(-/-) serum suggesting activation could also take place in the absence of a functional alternative pathway. Furthermore, we uncovered a role for C4 in the alternative pathway activation by Cryptococcus spp. We also identified an unexpected and complex role for MBL in complement activation by Cryptococcus spp. No complement activation occurred in the absence of MBL-A and -C proteins although activation took place when the lectin binding activity of MBL was disrupted by calcium chelation. In addition, alternative pathway activation by C. neoformans required both MBL-A and -C, while either MBL-A or -C was sufficient for alternative pathway activation by C. gattii. Thus, complement activation by Cryptococcus spp. can take place through multiple pathways and complement activation via the alternative pathway requires the presence of C4 and MBL proteins.

Aureobasidium pullulans var. melanigenum fungemia in a pediatric patient.

This report describes a chronically ill child who presented with high fever and was diagnosed with catheter-related sepsis. Aureobasidium pullulans variety melanigenum, a dematiaceous fungus that rarely causes opportunistic infections, was recovered from multiple blood cultures. Antifungal susceptibilities were performed and the minimum inhibitory concentration (MIC) for fluconazole was 64 mg/l, suggestive of fluconazole resistance. The patient made a full recovery after removal of the catheter line and treatment with liposomal amphotericin B. This is the first case report of an elevated in vitro fluconazole MIC of an A. pullulans isolate and only the third case of successful treatment of A. pullulans fungemia.