Clonality Analysis of Streptococcus pneumoniae in Clinical Specimens

Pneumococcal pneumonia is a significant cause of illness and death globally, particularly among young children and the elderly. The cpsB gene is involved in the biosynthesis of the capsule polysaccharide, and polymorphisms in the cpsB gene are the basis for sequetyping, a molecular biology-based approach to serotyping. In this study, we attempted the sequetyping of pneumococci directly from clinical sputum specimens collected from adult patients diagnosed with community-acquired pneumonia (CAP). We performed conventional PCR for the cpsB gene, followed by TA cloning and Sanger sequencing of the amplicon. The results showed the status of clonality of pneumococci in each specimen. We also performed real-time PCR targeting pneumococci for each specimen. It revealed a significant association between the Ct value of the real-time PCR and the clonality status of pneumococci among the specimens (p-value 0.0007 by Fisher's exact test analysis). Specifically, when the Ct value was below 22, there was a high probability that pneumococcus existed as a single clone. Thus, this study demonstrates the possible correlation between pneumococcal clonality and bacterial load in clinical specimens, which might indicate the infection status.