Fungistatic Action of N-Acetylcysteine on Candida albicans Biofilms and Its Interaction with Antifungal Agents

Therapies targeted to fungal biofilms, mainly against the matrix, and therapies that do not induce microbial resistance are relevant. N-acetylcysteine (NAC), a mucolytic agent, has shown antimicrobial action. This study evaluated the effect of NAC against fluconazole-susceptible (CaS) and -resistant (CaR) Candida albicans. The susceptibility of planktonic cultures to NAC, the effect of NAC on biofilms and their matrix, the interaction of NAC with antifungal agents, and confocal microscopy were evaluated. Data were analyzed descriptively and by the ANOVA/Welch and Tukey/Gomes–Howell tests. The minimum inhibitory concentration (MIC) of NAC was 25 mg/mL for both strains. NAC significantly reduced the viability of both fungal strains. Concentrations higher than the MIC (100 and 50 mg/mL) reduced the viability and the biomass. NAC at 12.5 mg/mL increased the fungal viability. NAC also reduced the soluble components of the biofilm matrix, and showed synergism with caspofungin against planktonic cultures of CaS, but not against biofilms. Confocal images demonstrated that NAC reduced the biofilm thickness and the fluorescence intensity of most fluorochromes used. High concentrations of NAC had similar fungistatic effects against both strains, while a low concentration showed the opposite result. The antibiofilm action of NAC was due to its fungistatic action.

Antifungal activity of chitosan and its quaternized derivative in gel form and as an edible coating on cut cherry tomatoes

The antifungal activities of medium molecular weight chitosan and its hydrosoluble derivative salt N,N,N-trimethylchitosan were examined as both gel and as a solid protective coating against three common food spoilage fungi (Penicilliumsp., wild Aspergillussp. and one standard strain of Aspergillusflavus). The salt derivative is characterized by having permanent positive charges and is expected to have a higher antimicrobial activity than commercial chitosan. In gel form, the minimum inhibitory concentration (MIC) resulted in the same value for both polymers against all tested fungi (> 2.0 gl-1). The derivative presented a significant fungistatic action against the Penicillium strain within the concentration range of 0.2 to 0.6 gl-1. When applied as protective coatings on freshly cut cherry tomatoes, the commercial chitosan appeared to be more effective in forming stable films and preventing fungal infestation than its derivative. Less than 20?25% of samples were infected after one week of incubation when compared to control (uncoated) and chitosan treated samples.