Magnetic bead-based separation of pneumococcal serotypes

Abstract

Summary: The separation of pneumococcal serotypes from a complex polymicrobial mixture may be required for different applications. For instance, a minority strain could be present at a low frequency in a clinical sample, making it difficult to identify and isolate by traditional culture-based methods. We therefore developed an assay to separate mixed pneumococcal samples using serotype-specific antiserum and a magnetic bead-based separation method. Using qPCR and colony counting methods, we first show that serotypes (12F, 23F, 3, 14, 19A, and 15A) present at ∼0.1% of a dual serotype mixture can be enriched to between 10% and 90% of the final sample. We demonstrate two applications for this method: extraction of known pneumococcal serotypes from saliva samples and efficient purification of capsule switch variants from experimental transformation experiments. This method may have further laboratory or clinical applications when the selection of specific serotypes is required. Motivation: Use of molecular methods has improved identification of pneumococci in saliva samples; however, isolating pneumococcus, particularly from mixed/complex samples, can be challenging. We developed a magnetic bead-based separation method to enrich samples for pneumococci in order to make isolation easier and less labor intensive.

Keywords

• CP: Microbiology