Precision delivery of antibiofilm therapies using Candida-sensing probiotic yeast

ABSTRACT Fungal infections, particularly Candida albicans (Ca), have a high worldwide disease burden and mortality rate. Unfortunately, antifungal resistance is rising in this pathogen, necessitating the search for alternative treatment modes. Ca can exist in the gut of healthy individuals without causing disease, but can also switch into a pathogenic form. Key drivers of Ca virulence include hyphal growth and biofilm formation that is enforced by its mating pheromone, α-factor. Unfortunately, biofilm formation also reduces the efficacy of antifungal drugs. Therefore, drugs that inhibit the ability of C. albicans to form biofilms in the gut may synergize with currently available therapies to treat Candida infections. Excitingly, Ca biofilms can be inhibited with synthetic peptides or biofilm-degrading enzymes. However, because protein drugs are susceptible to degradation in the gut, delivery of these drugs remains a challenge. Targeted delivery strategies such as liposomes or nano-lipid carriers are promising candidates for this purpose, but release their therapeutic cargo in response to rather crude signals (e.g. mucus or pH) which are relatively uniform in the large intestine. Engineered probiotic microbes are a promising vehicle for delivery of protein drugs into the large intestine. Recent advances in our ability to engineer non-model microbes, as well as an increased understanding of the gut microbiota, have led to a renewed focus in these therapies. Engineered probiotics achieve site-specific protein delivery due to the ability to sense highly specific extracellular cues (e.g. peptide hormones), localize to defined regions of the gut by displaying adhesins on their surface, and secreting recombinant proteins extracellularly. For the purposes of treating Ca biofilms, the probiotic yeast Saccharomyces boulardii (Sb) is particularly promising because of its high secretion rates, ability to easily display recombinant proteins on its cell surface, and its ability to express receptors for the Ca mating pheromone. In this study, we will develop strains of probiotic yeast that can bind to Ca biofilms, secrete biofilm-inhibiting proteins, and sense peptides secreted by Ca during biofilm formation. In doing so, we will generate a lead live biotherapeutic against Ca biofilms that is ready for testing in preclinical models of gut-derived candidiasis.