A non-contact co-culture method for studying metabolic interactions in the human microbiome

Neisseria meningitidis is a commensal of the upper respiratory tract (URT) that can sporadically cause invasive meningococcal disease (IMD). Utilisation of propionic acid by N. meningitidis is a known pathogenicity factor, and N. meningitidis is associated with propionic acid-producing bacteria of the URT microbiome, in particular Porphyromonas. An in vitro non-contact co-culture assay is proposed to study metabolic interactions between N. meningitidis and Porphyromonas gingivalis via propionic acid. This assay is modelled using ordinary differential equations showing that it is feasible when permeability of oxygen and propionic acid is balanced, and that quantification can be achieved only when N. meningitidis growth is limited by both oxygen and propionic acid. Parameter values from a verified model, fitted to in vitro data, would quantify the metabolic interaction. The apparatus was designed using limits and rules discovered by the model analysis, and by an iterative development process. The ability to capture N. meningitidis growth dynamics, and generate anaerobic conditions for P. gingivalis, was demonstrated. Growth inhibition by propionic acid, and yields of N. meningitidis from glucose, pyruvate and propionic acid were measured. Other important aspects of N. meningitidis growth were identified using plate reader experiments. The developed assay is not fully demonstrated. However, all results indicate that it is suitable for quantifying metabolic interactions between the aerobic N. meningitidis and the anaerobic P. gingivalis. Insights into this metabolic interaction would be useful for developing novel therapeutics to prevent IMD. This methodology is also of general interest for studying metabolic interactions in the human microbiome.