Magnetic Bead-Based Separation (MBS) of Pneumococcal Serotypes

There is often a need to separate a specific serotype of pneumococcus from a complex mixture of other pneumococcal strains. For instance, there could be a minority strain present at a low frequency in the nasopharynx that is difficult to identify and isolate by traditional culture. Or there might be a need to detect a minority serotype that has switched capsules in clinical samples or in laboratory experiments. We therefore developed a novel assay to separate mixed pneumococcal samples using serotype-specific antiserum and a magnetic bead-based separation method. We show using qPCR and colony counting methods, that six serotypes (12F, 23F, 3, 14, 19A and 15A) present as ~0.1% of a dual serotype mixture can be enriched to between 10% and 90% of the final sample. This method is an important development for laboratory techniques which select for certain target serotype such as transformation and co-colonization experiments. With further development, this method has potential for clinical applications such as isolating pneumococcal strains from clinical samples. ### Competing Interest Statement DMW has received consulting fees from Pfizer, Merck, GSK, and Affinivax and is PI on research grants from Pfizer and Merck to Yale. ALW has received consulting fees from Pfizer and is PI on research grants from Pfizer to Yale. The other authors declare no conflict of interest.