Application of chitosan in the control of fungal infections by dermatophytes

Abstract

Dermatophytes are a goup of fungi that can invade keratinized tissues of humans and other animals and produce an infection - dermatophytosis. Dermatophytic infections are an important public health problem and to control them a prolonged therapy is required. But, the existing drugs seem to exhibit side effects and the frequent and prolonged use of these compounds is responsible for strain resistance, representing a potential risk for the environment and human health. Because of this features, new drug biocompatible formulations for long term use are required. Chitosan is a cationic, biocompatible polysaccharide that possess antimicrobial action. So, the main objective of this work was to evaluate the antifungal activity of chitosan upon some dermatophytes (T. rubrum and M. canis ) and some Aspergillus (A. terreus, A. niger, A. flavus and A. fumigatus). For this, the MIC of chitosans was determined and the results showed that chitosan possesses antifungal activity against T. rubrum and M. canis, presenting MIC ranging from 1.1 to 2.2 mg/mL. For Aspergillus species, in the range of tested concentrations it was not possible to determine the chitosan's MICs. Minimum fungicidal concentrations were also obtained for both dermatophytes, corresponding in both cases to the values obtained for MIC. As dermatophytes are responsible for infections of keratinized surfaces, is crucial to understand if chitosan exert any effect on fungi activity. The analysis of SEM images showed that chitosan seems to have a protective effect of the hair (substract), when this was infected with dermatophytes. The study of the effect of chitosan on enzymatic activity using protease K showed an important activity in preventing proteases action. The effect of chitosan on keratin degradation by M. canis and T. rubrum, was also studied by keratin-azure test and the results showed that the dye release is reduced when chitosan is present in culture media. A microscopic analysis of keratin-azure surface when chitosan was present in the culture media corroborated the previous conclusion, because keratin-azure surface treated with chitosan showed no damage, despite the existence of fungal structures around them. Based on the obtained results, it´s possible to conclude that chitosan showed relevant antifungal activity against dermatophytes, which opens good prospects to chitosan as an alternative for the usual tinea treatments.

Date of Award	25 Sept 2013
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Maria Manuela Pintado (Supervisor) & Freni Tavaria (Co-Supervisor)