In vitro susceptibility testing for black grain eumycetoma causative agents

Area of Science:

• Medical Mycology
• Tropical Diseases
• Antimicrobial Resistance

Background:

• Eumycetoma is a neglected tropical mycosis causing subcutaneous swellings, with causative agents found in grains within infected tissue.
• The most common eumycetoma agents produce black grains and are sterile in culture, complicating diagnosis and treatment.
• Standardized in vitro susceptibility assays are needed to guide antifungal therapy for eumycetoma.

Purpose of the Study:

• To evaluate the utility of in vitro susceptibility assays for eumycetoma causative agents in drug discovery and clinical decision-making.
• To assess the correlation between in vitro antifungal activity and therapeutic efficacy in a model system.
• To determine the feasibility of establishing clinical breakpoints for eumycetoma treatment.

Main Methods:

• In vitro susceptibility assays were developed based on the Clinical and Laboratory Standards Institute M38A protocol, modified for hyphal inoculum.
• Viability dyes like resazurin or XTT were employed to facilitate endpoint determination.
• Antifungal compound efficacy was tested against eumycetoma agents, and results were compared with Galleria mellonella larval survival models.

Main Results:

• The assays successfully determined antifungal inhibition and were useful for drug discovery by identifying compounds preventing hyphal growth.
• A clear correlation between in vitro measures (MIC50) and therapeutic efficacy in the Galleria mellonella model was not established.
• While some agents showed MIC50 values below attainable serum levels (e.g., itraconazole), clinical breakpoints are yet to be defined.

Conclusions:

• In vitro susceptibility assays are valuable for antifungal drug discovery against eumycetoma agents.
• Further research is required to correlate in vitro results with clinical outcomes before these assays can guide mycetoma treatment decisions.
• Establishing clinical breakpoints is essential for the effective use of in vitro susceptibility data in managing eumycetoma.