AUTHOR=Powell Lydia C. , Adams Jennifer Y. M. , Quoraishi Sadik , Py Charlène , Oger Anaϊs , Gazze Salvatore A. , Francis Lewis W. , von Ruhland Christopher , Owens David , Rye Philip D. , Hill Katja E. , Pritchard Manon F. , Thomas David W. 

TITLE=Alginate oligosaccharides enhance the antifungal activity of nystatin against candidal biofilms

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2023.1122340

DOI=10.3389/fcimb.2023.1122340

ISSN=2235-2988

ABSTRACT=<sec><title>Background</title><p>The increasing prevalence of invasive fungal infections in immuno-compromised patients is a considerable cause of morbidity and mortality.  With the rapid emergence of antifungal resistance and an inadequate pipeline of new therapies, novel treatment strategies are now urgently required.</p></sec><sec><title>Methods</title><p>The antifungal activity of the alginate oligosaccharide OligoG in conjunction with nystatin was tested against a range of <italic>Candida</italic> spp. (<italic>C. albicans</italic>, <italic>C. glabrata</italic>, <italic>C. parapsilosis</italic>, <italic>C. auris</italic>, <italic>C. tropicalis</italic> and <italic>C. dubliniensis</italic>), in both planktonic and biofilm assays, to determine its potential clinical utility to enhance the treatment of candidal infections.  The effect of OligoG (0-6%) ± nystatin on <italic>Candida</italic> spp. was examined in minimum inhibitory concentration (MIC) and growth curve assays.  Antifungal effects of OligoG and nystatin treatment on biofilm formation and disruption were characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) and ATP cellular viability assays.  Effects on the cell membrane were determined using permeability assays and transmission electron microscopy (TEM).</p></sec><sec><title>Results</title><p>MIC and growth curve assays demonstrated the synergistic effects of OligoG (0-6%) with nystatin, resulting in an up to 32-fold reduction in MIC, and a significant reduction in the growth of <italic>C. parapsilosis</italic> and <italic>C. auris</italic> (minimum significant difference = 0.2 and 0.12 respectively).  CLSM and SEM imaging demonstrated that the combination treatment of OligoG (4%) with nystatin (1 µg/ml) resulted in significant inhibition of candidal biofilm formation on glass and clinical grade silicone surfaces (<italic>p</italic> &lt; 0.001), with increased cell death (<italic>p</italic> &lt; 0.0001).  The ATP biofilm disruption assay demonstrated a significant reduction in cell viability with OligoG (4%) alone and the combined OligoG/nystatin (MIC value) treatment (<italic>p</italic> &lt; 0.04) for all <italic>Candida</italic> strains tested.  TEM studies revealed the combined OligoG/nystatin treatment induced structural reorganization of the <italic>Candida</italic> cell membrane, with increased permeability when compared to the untreated control (<italic>p</italic> &lt; 0.001).</p></sec><sec><title>Conclusions</title><p>Antimicrobial synergy between OligoG and nystatin against Candida spp. highlights the potential utility of this combination therapy in the prevention and topical treatment of candidal biofilm infections, to overcome the inherent tolerance of biofilm structures to antifungal agents.</p></sec>