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Development of an in vitro, isolated, infected spore testing model for disinfectant testing of Microsporum canis
Karen A Moriello1, Douglas J Deboer, Lynn M Volk
1Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Drive West, Madison, WI 53706, USA. moriellk@svm.vetmed.wisc.edu
Abstract:
The isolated infected hair model is a commonly used technique to test the fungicidal efficacy of topical therapies against Microsporum canis. The most commonly used model uses mats of infective hairs, and results from various laboratories have differed. The objectives of this study were to develop a method to produce spores for testing when only mycelial forms were available and to develop a semiquantitative testing method that used only infective spores from hairs, and not pooled hair samples for testing. Ten isolates of M. canis were used in this study. Juvenile guinea pigs were easily infected using mycelial forms of M. canis and large numbers of spores were easily harvested for testing. Eight dilutions of disinfectants were tested. Fungal culture data were evaluated using an endpoint dilution at which there was 100% fungicidal activity, i.e. no growth on the plates. The 10 samples showed identical results. Chlorhexidine and Virkon(R) S were ineffective even when used at x4 the manufacturer's recommended dilution. Lime sulphur (1 : 33), enilconazole (20 microL mL(-1)), and bleach (1 : 10) were consistently effective when used at the recommended dilution. In addition, lime sulphur and enilconazole were 100% fungicidal even when the recommended concentration was diluted 1 : 4 or x4 as dilute as recommended.
Insights
This study developed a new method for testing topical treatments against Microsporum canis. Lime sulphur and enilconazole proved effective, even at diluted concentrations, for controlling fungal infections.
Area of Science:
- Veterinary Mycology
- Antifungal Efficacy Testing
- Dermatophytosis Research
Background:
- The isolated infected hair model is standard for testing topical antifungals against Microsporum canis.
- Existing methods using pooled hair samples yield variable results.
- A need exists for a standardized, spore-based testing method.
Purpose of the Study:
- To develop a method for producing Microsporum canis spores from mycelial forms.
- To establish a semiquantitative testing protocol using only hair-borne spores.
- To evaluate the fungicidal efficacy of various disinfectants against M. canis.
Main Methods:
- Ten isolates of Microsporum canis were cultured and used to infect juvenile guinea pigs.
- Spores were harvested from infected hairs for semiquantitative testing.
- Eight dilutions of disinfectants were tested, with fungicidal activity determined by lack of growth on culture plates.
Main Results:
- Lime sulphur (1:33), enilconazole (20 µL/mL), and bleach (1:10) were effective at recommended dilutions.
- Chlorhexidine and Virkon S were ineffective, even at four times the recommended dilution.
- Lime sulphur and enilconazole maintained 100% fungicidal activity when diluted fourfold.
Conclusions:
- A reliable method for producing and testing M. canis spores from infected hairs was developed.
- Lime sulphur and enilconazole demonstrate superior fungicidal efficacy against M. canis compared to chlorhexidine and Virkon S.
- These findings support the use of lime sulphur and enilconazole for topical treatment of M. canis infections.
