Galleria mellonella in antimicrobial drug discovery: bioactive substances extracted from probiotic against Candida albicans persisters

Abstract

In the last years, conventional antifungal screening strategies have failed to yield new classes of effective antimicrobials. New paradigms for discovering novel antimicrobial agents are needed. Ideally, new agents should be effective against persisters cells, the subpopulation of fungal cells that show tolerance to conventional drugs. This is clinically important because persister cells are responsible for recurrent infections, such as oral candidiasis. Oral candidiasis is one of the most common human fungal infections and some in vitro studies have shown that Lactobacillus can produce bioactive substances capable of inhibiting C. albicans, becoming interesting the identification and development of new substances for the treatment of oral candidiasis. Thus, in vivo studies are important tools for assessing pathogenicity of Candida species and to evaluate the effectiveness of these alternative treatments. An animal host model can mimic the pathogenesis of infection in humans, including colonization, invasion and interaction with the host's immune system. In this context, Galleria mellonella has been considered a suitable host model that can optimize the translation of drug discoveries from in vivo studies to mammalian diseases. The objective of this study is to evaluate the metabolites produced by L. paracasei 28.4 on C. albicans persisters through induction of experimental candidiasis in invertebrate model of G. mellonella. Ten clinical strains of C. albicans isolated from oropharyngeal candidiasis lesions of HIV-positive patients and from patients with invasive candidiasis will be studied. Firstly, persisters cells in C. albicans biofilms will be isolated. C. albicans persisters will be inoculated in G. mellonella and treated with crude extract and the identified fractions of L. paracasei 28.4 supernatant. The experimental infection will be assessed by survival curves, hemocyte density, cellular characterization of hemocytes by flow cytometry and by detection of C. albicans infection in real time, using bioluminescence assay. The results will be analyzed for selecting the best statistical test for each analysis of this study, considering a significance level of 5% test.