P076 The promising antimycotic activities of a novel cyclic antifungal lipopeptide against Human Dermatophyte Isolates

Abstract

Poster session 1, September 21, 2022, 12:30 PM - 1:30 PM Objectives To determine the minimum inhibitory concentrations (MICs) of a novel antifungal lipopeptide against clinical isolates of dermatophytes of human origin. Methods To perform antifungal susceptibility testing (AFST) by CLSI microbroth dilution method, a reversed-phase high-performance liquid chromatography (RP-HPLC) purified lipopeptide of 1071.4 Da from a wild-type soil isolate Bacillus subtilis was used and compared with the standard allylamine terbinafine MICs. Briefly, 1200 ml of cell-free culture supernatant was extracted using a solvent mixture and silica gel (230-400 mesh size)-based adsorption chromatography. The semi-preparative RP-HPLC system consisted of an Agilent quaternary pump and a variable wavelength detector equipped with a Phenomenex Luna C18 column (10 mm × 250 mm, 5 μm). The solvent system for RP- HPLC was (A) water with 0.1% trifluoroacetic acid (TFA) and (B) acetonitrile containing 0.1% TFA. The gradient of solvent B used for purification was as follows: 0%-54% for 0-20 min at the flow rate of 1 ml/min, 54%-60% from 20-48 min at 0.5 ml/min, 60%-100% from 48-58 min at 0.5 ml/min, 100%-0% from 58-65 min at 1 ml/min and monitored at 210 nm. Results Superficial skin infections are caused by dermatophytes including Trichophyton spp. Nowadays, resistance to terbinafine in Trichophyton spp. isolates with higher MICs have been documented in India. We report here the antifungal prowess of a novel small antifungal lipopeptide against 20 clinical isolates of Trichophyton spp. of human origins (from human skin scrapings and nails) with the clinical diagnosis of tinea corporis/cruris and tinea unguium. The representative photographs of T. tonsurans, T. rubrum, and T. mentagrophytes complex are provided below. A total of 6 isolates of T. mentagrophytes and T. rubrum carry point mutations at F397L of squalene epoxidase (SQLE) protein. The in vitro antifungal efficacies determined by AFST revealed that the lipopeptide showed less or equivalent MICs (100% inhibition) in the case of five dermatophytes. The lipopeptide drug has exhibited improved MICs against two T. mentagrophytes complex and two T. rubrum isolates with amino acid substitution F397L in SQLE protein. Trichophyton mentagrophytes complex and T. rubrum with F397L mutations were inhibited at MICs 4-32 μg/mL of terbinafine. In comparison, the lipopeptide showed 4-16 μg/ml (100% inhibition). In the case of all four Trichophyton tonsurans, the MICs ranged between 2-4 μg/ml for the lipopeptide. Conclusions The broad-spectrum lipopeptide showed promising antifungal activity against dermatophytes and may be considered for nano-emulsion formulation and tested for topical application in a mice model.