Comparative genomic and morphological analyses of capsular and capsular-deficient pneumococcal strains simultaneously isolated from a patient with invasive pneumococcal disease.

Introduction: To understand the in-vivo dynamics in pneumococci, investigation into the carriage in patients with invasive pneumococcal disease (IPD) is extremely important.

Methods: To clarify genomic and morphological differences between pneumococcal strains simultaneously isolated from different sites in a patient with IPD, we conducted comparative analyses of two strains. A capsular strain isolated from the blood and a non-capsular strain isolated from the sputum of a patient with IPD were used.

Results: The strain isolated from blood was serotype 24B with capsule. The strain isolated from sputum with capsular type 24 genes was non-encapsulated, and genomic analysis revealed an insertion region in the wcxK gene. Its biofilm-forming capacity was higher than that of the capsular strain, as was that of the pspK-positive true non-encapsulated strain. Furthermore, observing the microbe using transmission electron microscopy revealed that the strain isolated from sputum lacked a capsule, like the pspK-positive true non-encapsulated strain.

Conclusions: Our analysis of the two strains isolated from the blood and sputum of a patient with IPD showed one possible in-vivo morphological change in Streptococcus pneumoniae.