Antifungal effect of high- and low-molecular-weight chitosan hydrochloride, carboxymethyl chitosan, chitosan oligosaccharide and N-acetyl-D-glucosamine against Candida albicans, Candida krusei and Candida glabrata.

OBJECTIVES: Generally, chitosan is a water-insoluble polyaminosaccharide with antimicrobial activity. The antifungal activity of water-soluble low- and high-molecular-weight chitosan hydrochloride, carboxymethyl chitosan, chitosan oligosaccharide and N-acetyl-d-glucosamine against Candida albicans, Candida krusei and Candida glabrata was investigated.

METHODS: Solutions of the tested substances in different concentrations (1, 0.5, 0.25, 0.1, 0.05, 0.025, 0.01, 0.005, and 0.0025%) were prepared and the influence on C. albicans DSM 11225, C. krusei ATCC 6258 and C. glabrata DSM 11226 was investigated. Yeasts (3 x 10(5) cells/mL) were incubated with Sabouraud liquid medium at 30 degrees C. Measurements were done with a microplate nephelometer (NEPHELOstar Galaxy, BMG LABTECH Ltd.) for 24 h. High values of light scattering correlate with strong cultural growth. Results were shown as growth curves and histograms displaying 24 h end points. These were compared with control by Mann-Whitney test. Furthermore, MIC(50%), MIC(80%) and Spearman correlation coefficients were calculated.

RESULTS: C. albicans and C. krusei were the most sensitive species. C. glabrata was also inhibited, whereas 1% of tested substances could not prevent its growth completely. However, only both chitosan hydrochlorides showed a definite antifungal effect with high correlation between inhibition and test concentration. Carboxymethyl chitosan, chitosan oligosaccharide and N-acetyl-D-glucosamine showed only a weak or no antifungal activity, respectively.

CONCLUSIONS: Antifungal activity decreases with declining molecular mass (chitosan oligosaccharide and N-acetyl-D-glucosamine) and increasing masking of the protonated amino groups with functional groups (carboxymethyl chitosan).