Characterization of Streptococcus pneumoniae phage-like element SpnCI reveals an enhanced virulent phenotype in the acute invertebrate infection model Galleria mellonella

Abstract

AbstractPhage-like elements are found in a multitude of streptococcal species, including pneumococcal strain Hungary19A-6 (SpnCI). The aim of our research was to investigate the role of phage-like element SpnCI in enhanced virulence and phenotypic modulation within Streptococcus pneumoniae. SpnCI was found to significantly enhance virulence within the invertebrate infection model Galleria mellonella. Infections with SpnCI led to a lower mean health score (1.6) and survival percentage (20%) compared to SpnCI null TIGR4 infections (3.85 mean health score and 50% survival). SpnCI remained integrated throughout growth, conferring greater sensitivity to UV irradiation. Change in transcriptional patterns occurred, including downregulation of operons involved with cell surface modelling in the SpnCI containing strain of TIGR4. Kanamycin-tagged SpnCI strain in Hungary19A-6 was inducible and isolated from lysate along with both annotated prophages. No phages were identified by PCR nor electron microscopy (EM) following induction of TIGR4 SpnCIΔstrA suggesting helper-phage dependence for dissemination. EM of lysate showed typical siphoviridae morphology with an average capsid size of 60 nm. Two of sixty capsids were found to be smaller, suggesting SpnCI disseminates using a similar mechanism described for Staphylococcus aureus phage-like element SaPI. SpnCI from lysate infected capsule null strain T4R but was incapable of infecting the encapsulated TIGR4 strain suggesting that capsule impedes phage infection. Our work demonstrates that SpnCI can modulate virulence, UV susceptibility, alter transcriptional patterns, and furthermore, can disseminate via infection within pneumococcus. Further research is necessary to elucidate how SpnCI modulates virulence and what genes are responsible for the enhanced virulence phenotype.ImportanceAlthough vaccines have limited the scope of pneumococcal infections, Streptococcus pneumoniae still remains an important human pathogen. Understanding novel elements, such as SpnCI, that enhance virulence can lead to the development of more targeted therapeutic and diagnostic tools within the clinical realm.