An innovative microplate-based method to measure coaggregation between a model pair of coaggregating oral bacteria

Background Coaggregation is proposed to enhance oral biofilm development. This study aims to evaluate an innovative high-throughput spectrophotometric method for quantifying coaggregation, which relies upon dome-shaped wells (DSWs) in microplates to partition coaggregates in cell suspensions, and compare its utility against other established methods.Materials and methods Batch-cultured cells of Streptococcus gordonii DL1 and Actinomyces oris T14V were suspended individually in coaggregation buffer (Coag-B) or buffered KCl (B-KCl) for coaggregation experiments. Multiple methods were used to assess coaggregation between S. gordonii DL1 and A. oris T14V in the two buffers: the high-throughput spectrophotometric assay using modified 24-well microplates; visual aggregation assays; confocal microscopy; and cuvette-based spectrophotometry.Results In either buffer, S. gordonii DL1 and A. oris T14V coaggregated strongly in visual tube-based assays, although the coaggregates were typically larger and more condensed in B-KCl. This observation was supported by microscopy and cuvette-based measurements. Compared with other well/buffer combinations, coaggregation was most strongly and reproducibly detected in endpoint and kinetic studies when cells were suspended in B-KCl and added to DSWs.Conclusion Using DSWs in combination with B-KCl provided a high-throughput quantitative approach to study coaggregation between S. gordonii DL1 and A. oris T14V.