Rapid antifungal susceptibility testing from positive blood cultures using direct gradient diffusion: a prospective study.

OBJECTIVE

To evaluate the agreement between direct gradient diffusion (DGD), performed directly from positive blood culture bottles, and the Sensititre™ YeastOne™ (SYO) method for antifungal susceptibility testing in Candida spp.

METHODS

A prospective observational study including blood cultures positive for yeasts between June and October 2024 was conducted. DGD (ETEST®) was performed directly from blood culture broth and compared with SYO. The antifungal agents evaluated were anidulafungin, micafungin, caspofungin, fluconazole, voriconazole, and amphotericin B. Categorical agreement (CA) and essential agreement (EA) were analyzed.

RESULTS

A total of 32 Candida isolates were included. Overall CA was 90%, whereas EA was 60.6%. CA was 100% for amphotericin B, 92.5% for azoles, and 86% for echinocandins. No very major errors were observed. However, all Candida parapsilosis isolates showed major errors for anidulafungin, appearing resistant by DGD and susceptible by SYO. All DGD results were interpretable after 24 hours.

CONCLUSIONS

DGD performed directly from positive blood culture bottles provides early antifungal susceptibility results with high CA and markedly reduced turnaround time. However, caution is required when interpreting anidulafungin resistance in C. parapsilosis. This approach may serve as an adjunctive tool for early optimization of antifungal therapy.