Background: PLD-118 is a new, orally active antifungal agent of the beta-amino acid class, primarily active against yeasts. It shows no activity in standard assays for susceptibility testing of Candida spp., so special method based on YNG medium had to be developed. Similarly, PLD-118 was not active against dermatophytes in commonly used test (NCCLS standard for filamentous fungi), so efforts have been made to develop appropriate assay. Methods: Five clinical isolates of T. mentagrophytes were identified using standard methods. Testing was performed in two 24-well plates per strain. The final volume per well was 2 mL. Serial doubling dilutions of tested antifungals (PLD-118, terbinafine, miconazole and clotrimazole) were prepared in sterile distilled water with 0.1% of 10% yeast extract. Autoclaved human hairs were suspended in sterile normal saline and 20 µL of suspension added to each well. Inoculum was prepared according NCCLS standard for filamentous fungi. It was diluted with sterile distilled water. Plates were incubated for 3 weeks at 28°C. The MIC in the presence of keratin was defined as the lowest concentration of an agent used which inhibited visible growth. Testing was performed in duplicate. Results: All strains grew as a mycelium by invading the hairs. Highly reproducible MICs, comparable to that determined by NCCLS method, were obtained for terbinafine (0.03-0.06 µg/ml), clotrimazole (0.125-0.25 µg/ml) and miconazole (0.5-2 µg/ml). In contrast to NCCLS assay, PLD-118 showed activity against T. mentagrophytes (2-32 µg/ml), but between-run variations were in range of 1-4 dilutions. Conclusion: In vitro activity of PLD-118 against T. mentagrophytes has been shown in the presence of keratin. Developed assay was very reproducible for terbinafine, clotrimazole and miconazole, but further optimization would be needed for PLD-118.
Full conference title:
43rd Interscience Conference on Antimicrobial Agents
- ICAAC 43rd