[S6-2] Spontaneous phase shift during the establishment of pneumococcal colonization
Streptococcus pneumoniae frequently colonizes the human nasopharynx in the early childhood and causes various infectious diseases such as otitis media, rhinosinusitis, pneumonia and invasive disease. During the establishment of colonization and the development of infection, pneumococci exhibit a spontaneous and reversible phase shift between opaque and transparent to adapt to various environments. We evaluated the dynamics of pneumococcal phase shift during the course of adhesion and subsequent invasion into epithelial cell monolayers by bacteria-cell co-culture assay with a time-lapse microscopy. The invasion to the intercellular space of a transparent variant inoculum of pneumococci was strongly associated with its transformation into an opaque-like variant. However, the change was not observed when an opaque variant was cultured with epithelial cells in suspension. Sub-MIC levels of clarithromycin inhibited the spontaneous pneumococcal phase shift from a transparent to an opaque variant. The current findings show that the encapsulated pneumococcus can modulate its fitness in response to the environment during the establishment of colonization, providing a more in depth understanding of how the pneumococcal phase shift distributes to conquer the barrier of mucosal epithelium and colonize for the encapsulated pneumococci.