An Excised Prophage of Streptococcus Pneumoniae Mediates Adherence to Respiratory Epithelial Cell

Streptococcus pneumoniae is a leading cause of infectious disease globally. Serotype 19A ST320, being prevalent in many countries, often are resistant to multiple antibiotics, and have emerged worldwide to be important pathogens associated with invasive pneumococcal disease, pneumonia, acute otitis media, and hemolytic uremic syndrome. It was suggested that the serotype 19A ST320 strain was derived from a capsular switching event that occurred between an international Taiwan 19F-14 (ST236) strain and a serotype 19A strain. Clinically, we observed that serotype 19A ST320 was more virulent than its ancestral Taiwan 19F-14 (ST236) clones do. For example, serotype 19A ST320 has substantial invasive potential, in contrast to serotype 19F ST236. Serotype 19A ST320 strains also have been classified among pleuropneumonia strains, but serotype 19F ST236 strains have not. In our previous study, we observed that the serotype 19A ST320 strain exhibited improved colonizing ability compared to its ancestral Taiwan 19F-14 (ST236) strain. More importantly, genetic change from ST236 into ST320 confers a competitive advantage in nasopharyngeal colonization. The evolution of Taiwan 19F-14 (ST236) to serotype 19A ST320 provided the clone with increased capacity for host colonization. Using whole transcriptome comparison of the two strains (serotype 19A ST320 and Taiwan 19F-14 ST236) by high-throughput RNA-sequencing technology, we identified that a prophage (～18 kb) had higher expression in serotype 19A ST320. The prophage can excised from the chromosome as an extrachromosomal, close-circular form in serotype 19A ST320, but not in serotype 19F ST236. Inactivation of integrase gene of the prophage, which resulted in no spontaneous excision activity in serotype 19A ST320, decreased adherence to A549 cell compared with wild type and was outcompeted by wild type in a competition experiment of murine colonization model. We conclude that spontaneous induction of the prophage promote adherence during colonization within a host. The study hypothesizes that excised prophage will directly contribute to adherence or prophage excision will result in higher expression of other adherence-associated genes to indirectly contribute to adherence. The investigation will 1) demonstrate how spontaneous induction of this prophage contribute to adherence: directly or indirectly. If a gene associated with adherence is found, we will express it, generate antibody and perform antibody inhibition assay to investigate if this gene is an adhesin. 2) utilize prophage promotor fusions for monitoring spontaneous induction of prophage at a single cell in serotype 19A ST320 and its association with adherence. 3) understand whether the prophage form functional infective phage particles. 4) study whether transfer the prophage into a prophage-negative strain will increase adherence. This study will elucidate how bacteria and prophage interact and affect pneumococcal adherence, which is helpful for development of novel therapeutic agents or vaccination to prevent pneumococcal colonization and infection.

Project ID:PC10507-0264
External Project ID:MOST105-2314-B182-049-MY3