Anti-dermatophytic activities and time-kill kinetics of the methanol extracts of Napoleona imperialis Activités anti-dermatophytiques et cinétique de destruction temporelle des extraits méthanoliques de Napoleona imperialis

Abstract

Background: Dermatophytosis is one of the most common cutaneous infections in the world. This is a superficial fungal infection that pose public health challenges to man and animals. The objective of this study is to evaluate the anti-dermatophytic activities of the different parts of Napoleona imperialis extract against selected clinical dermatophytes isolated from school children in Anambra State, Nigeria.
Methodology: The pulverized materials of the authenticated plant parts were extracted using cold maceration method for 48 hours in methanol. Stock solutions of the extracts were prepared by dissolving 1000mg of the extract in 2ml of dimethylsulphoxide (DMSO) to obtain a final concentration of 500mg/ml, that was used to primarily screen the plant extracts for their anti-dermatophytic activities on the selected dermatophytes by the agar well diffusion method. For determining the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC), stock solution of the plant extracts was prepared by dissolving 10000mg of the extract in 2 ml of DMSO to attain a final concentration of 5,000 mg/ml, which was used to prepare different concentrations of the extract by 2-fold serial dilution. The extracts were then tested on selected dermatophytes consisting of two isolates of Trichophyton mentagrophytes, one isolate of Microsporum audouinii, one isolate of Microsporum canis, and two isolates of Microsporum ferrugineum. The time kill kinetics was also performed using standard method.
Results: The mean (±SD) inhibition zone diameter produced by the stem bark extract against the different dermatophytes at concentration of 500mg/ml was significantly higher than all other plant extracts used (p<0.05) with M. ferrugineum as the most susceptible. The MICs and MFCs were the same for the leaf, root, stem bark and seed extracts of the plant, which ranged from 31.25-250 mg/ml for M. audouinii; 62.5-250 mg/ml for M. canis, and 0.978-62.5 mg/ml for M. ferrugineum 2. Similarly, the MICs and MFCs were the same for the root extract of the plant against T. mentagrophyte 2 (62.5 mg/ml), stem bark extract against T. mentagrophyte 1 (3.912 mg/ml) and against T. mentagrophyte 2 (1.956 mg/ml). The seed extract against T. mentagrophyte 1 and against M. ferrugineum 1 also had the same MIC and MFC (15.625 mg/ml). In the time -kill assay, there was drastic reduction in the number of viable cells count within 0-1 hour, and at 8-hour time period, there were no viable cells.
Conclusion: Crude methanol extracts of N. imperialis stem bark exhibited higher fungicidal effect when compared to the other plant parts. This extract can be a complementary source of novel antifungal agents. The study provides evidence for the use of this plant in traditional settings for the treatment of dermatophytosis.