A flow cytometry method for quantitative measurement and molecular investigation of the adhesion of bacteria to yeast cells

Abstract The interaction of bacteria with yeasts deserves great interest in animal and human welfare. To investigate these microbial interactions at the cellular and molecular level, a simple, reliable and quantitative method is proposed. We showed that flow cytometry enables the interaction to be measured at single cell level,by distinguishing single yeast cells with fluorescent bound bacteria from cell aggregates. free fluorescent bacteria Flow cytometry coupled with imaging showed that number of bacteria attached to yeast followed a Gaussian distribution with a maximum of 14, at a high bacteria: yeast ratio. Although the dynamic of adhesion resembles a Langmuir adsorption model, we found that this adhesion is a rapid and almost irreversible process that involves mannose-specific type 1 fimbriae, since mutants lacking these appendages no longer adhered to yeast. Furthermore, attachment of bacteria to yeast likely involved factors in addition to mannosyl sugars of the cell wall since yeast mutants with alteration in mannans content did not show difference in adhesion as compared to wild type. In summary, flow cytometry is an appropriate method for studying the mechanisms of interaction between bacteria and yeast, as well as for the high-throughput screening of candidate molecules likely to promote or counteract this interaction.