W27 IgA suppresses growth of Escherichia in an in vitro model of the human intestinal microbiota.

W27 monoclonal immunoglobulin A (IgA) suppresses pathogenic Escherichia coli cell growth; however, its effect on the human intestine remains unclear. We aimed to determine how W27 IgA affects the human colonic microbiota using the in vitro microbiota model. This model was established using fecal samples collected from 12 healthy volunteers; after anaerobic cultivation, each model was found to retain the genera found in the original human fecal samples. After pre-incubating W27 IgA with the respective fecal sample under aerobic conditions, the mixture of W27 IgA (final concentration, 0.5 μg/mL) and each fecal sample was added to the in vitro microbiota model and cultured under anaerobic conditions. Next-generation sequencing of the bacterial 16S rRNA gene revealed that W27 IgA significantly decreased the relative abundance of bacteria related to the genus Escherichia in the model. Additionally, at a final concentration of 5 μg/mL, W27 IgA delayed growth in the pure culture of Escherichia coli isolated from human fecal samples. Our study thus revealed the suppressive effect of W27 IgA on the genus Escherichia at relatively low-concentrations and the usefulness of an in vitro microbiota model to evaluate the effect of IgA as a gut microbiota regulator.