Enhancing effect of chitosan on methylene blue-mediated photodynamic therapy against C. albicans: A study in planktonic growth, biofilms, and persister cells.

Chitosan (CS) is a natural polymer extracted from the exoskeleton of crustaceans. Due to its cationic structure, CS has been studied as a possible enhancer of antimicrobial photodynamic therapy (aPDT). The objective was to evaluate the association of CS with methylene blue (MB)-mediated aPDT on Candida albicans, investigating its effects on planktonic growth, biofilms, and cells persistent to fluconazole. The ability of CS to interfere with MB absorption by Candida cells was also evaluated. For the assays, planktonic cells of C. albicans were cultivated for 24 h, and the biofilms were formed for 48 h. For the induction of persister cells, C. albicans was cultivated with high concentration of fluconazole for 48 h. Treatments were performed with MB, CS or MB+CS, followed by irradiation with LED (660 nm ). As results, aPDT with MB (300 µm) reduced the planktonic cells by 1.6 log10 CFU, while the MB+CS association led to a reduction of 4.8 log10 CFU. For aPDT in biofilms, there was a microbial reduction of 2.9 log10 CFU for the treatment with MB (600 µm) and 5.3 log10 CFU for MB+CS. In relation to persister cells, the fungal reductions were 0.4 log10 CFU for MB and 1.5 log10 CFU for MB+CS. In the absorption assays, the penetration of MB into Candida cells was increased in the presence of CS. It was concluded that CS enhanced the antimicrobial activity of aPDT in planktonic growth, biofilms, and persister cells of C. albicans, probably by facilitating the penetration of MB into fungal cells.

Galleria mellonella as an experimental model to study human oral pathogens.

The oral cavity is home to a microbial community of more than 800 species. This important microbiome is formed by commensal and opportunistic bacteria, fungi and viruses. Several distinct habitats within the mouth support heterogeneous microbial communities that constitute an important link between oral and general health. The use of animal models for in vivo studies in microbial pathogenicity is well established in the scientific community. Galleria mellonella as a model host has increased in use significantly in the last few years. This invertebrate model provides studies on a large scale, serving as screens for studies on vertebrate animals, such as mice and rats. In this review, different studies of microbial genera of dental importance (Enterococcus, Candida, Lactobacillus, Porphyromonas and Streptococcus) are discussed, highlighting the use of G. mellonella as a suitable model for studying pathogenesis, efficacy of antimicrobial compounds, and immune responses.