In Vitro Exploration of Probiotic Bacteria Interactions with Candida Using Culture Techniques to Model Dysbiotic Conditions in Colonized Tissues

Candida albicans overgrowth at various mucosal sites is an ongoing and complex clinical concern involving interactions with indigenous microbiota and therapeutic or preventive measures superimposed on the pathogen-microbiome interaction. In this paper we describe the use of quantitative flow cytometry (specific to the cytometer’s sample introduction mechanism) to explore the in vitro interaction between Candida albicans, probiotic lactobacilli and a topical vaginal therapeutic. Our central hypothesis was cytometric measurements of co-cultures of yeast and bacteria could provide a useful method for exploring the dynamics of different microbial species in culture, with and without inhibitors. Two commercial products were used as exemplars for this research, a vaginal antimicrobial gel and two species of probiotic lactobacillus intended or oral administration with crystalline bovine lactoferrin to augment the vaginal gel. The cytometer forward channel height parameter distinguished yeast from bacteria in co-culture experiments in the presence of a vaginal therapeutic gel or components of its formulation including EDTA, glycogen, polydextrose as well as the host defense factor, lactoferrin. Flow cytometry showed lactobacilli influenced yeast counts in co-culture, with the technique lending itself to wide-ranging test conditions including organisms, media composition and screening of various antimicrobials. Key findings: The proprietary vaginal gel augmented the effect of lactobacilli, as did EDTA and lactoferrin. Prebiotic compounds also enhanced Candida inhibition by lactobacilli. Propidium iodide (Fluorescence channel 3) discriminated between necrotic and non-necrotic yeast and bacteria in co-cultures under various culture conditions. This research demonstrates the value of flow cytometry to evaluate the population dynamics of yeast and bacteria in co-culture using a proprietary product and its components. We discuss both the limitations of the current study and describe how methods employed here would be transferrable to the investigation of organisms present in defined cultures or at body sites colonized by fungal species and the effects of therapeutics or probiotics on Candida.