Cell Viability Assays for Candida auris

Dry Surface Biofilm Formation by Candida auris Facilitates Persistence and Tolerance to Sodium Hypochlorite

Candida auris is an enigmatic fungal pathogen, recently elevated as a critical priority group pathogen by the World Health Organisation, linked with its ability to cause outbreaks within nosocomial care units, facilitated through environmental persistence. We investigated the susceptibility of phenotypically distinct C. auris isolates to sodium hypochlorite (NaOCl), and evaluated the role of biofilms in surviving disinfection using a dry-surface biofilm (DSB) model and transcriptomic profiling. Planktonic cells were tested for susceptibility to NaOCl, with biofilm formation using the 12-day DSB model, assessed using viable counts, biomass assays and microscopy. Disinfection efficacy was assessed using clinical protocols of 500-1,000 ppm for 1-5 min. RNA sequencing was performed on untreated DSBs in comparison to planktonic cells. Isolates were found to be susceptible planktonically, but grew NaOCl-tolerant biofilms, with only 2-4 log10 reductions in viable cells observed at highest concentrations. Transcriptomics identified DSB upregulation of ABC transporters and iron acquisition pathways relative to planktonic cells. Our findings optimized a DSB protocol in which C. auris can mediate tolerance to NaOCl disinfection, suggesting a lifestyle through which this problematic yeast can environmentally persist. Mechanistically, it has been shown for the first time that upregulation of small-molecule and iron transport pathways are potential facilitators of environmental survival.

Informed development of a multi-species biofilm in chronic obstructive pulmonary disease

Recent evidence indicates that microbial biofilm aggregates inhabit the lungs of COPD patients and actively contribute towards chronic colonization and repeat infections. However, there are no contextually relevant complex biofilm models for COPD research. In this study, a meta-analysis of the lung microbiome in COPD was used to inform development of an optimized biofilm model composed of genera highly associated with COPD. Bioinformatic analysis showed that although diversity matrices of COPD microbiomes were similar to healthy controls, and internal compositions made it possible to accurately differentiate between these cohorts (AUC = 0.939). Genera that best defined these patients included Haemophilus, Moraxella and Streptococcus. Many studies fail to account for fungi; therefore, Candida albicans was included in the creation of an interkingdom biofilm model. These organisms formed a biofilm capable of tolerating high concentrations of antimicrobial therapies with no significant reductions in viability. However, combined therapies of antibiotics and an antifungal resulted in significant reductions in viable cells throughout the biofilm (p < 0.05). This biofilm model is representative of the COPD lung microbiome and results from in vitro antimicrobial challenge experiments indicate that targeting both bacteria and fungi in these interkingdom communities will be required for more positive clinical outcomes.

Investigating Dual-Species Candida auris and Staphylococcal Biofilm Antiseptic Challenge

Candida auris can persistently colonize human skin, alongside a diverse bacterial microbiome. In this study we aimed to investigate the efficacy of antiseptic activities on dual-species interkingdom biofilms containing staphylococci to determine if antiseptic tolerance was negatively impacted by dual-species biofilms. Chlorhexidine, povidone iodine, and hydrogen peroxide (H₂O₂), were able to significantly reduce biofilm viable cell counts following exposure at 2%, 10%, and 3%, respectively. Notably, H₂O₂-treated biofilms were able to significantly recover and considerably repopulate following treatment. Fortunately, inter-kingdom interactions in dual-species biofilms of C. auris and staphylococci did not increase the tolerance of C. auris against antiseptics in vitro. These data indicate mixed infections are manageable with chlorhexidine and povidone iodine, but caution should be exercised in the consideration of H₂O₂.