Lack of Middle Ear Virulence of Streptococcus pneumoniae 33F Isolates in Chinchillas is Associated with Absence of the PsrP Pathogenicity Island
Methods: We screened more than 10 selected serotypes of Streptococus pneumoniae in our chinchilla model of experimental otitis media (EOM), initially using nasopharyngeal inoculation followed by barotrauma and subsequently with direct intrabullar challenge. Genomic DNA of these isolates was extracted by standard methods and sequenced using the HiSeq Illumina platform. De novo assembled sequences were annotated with RAST (Rapid Annotation by Subsystem Technology). Functional comparative genomic analysis was performed in SEED viewer; genes of subsystems identified as uniquely absent in 33F strains underwent detailed analysis in SEED, BRIG and BLAST.
Results: The serotype 33F isolates colonized the nasopharynx comparable to all other serotypes but failed to produce either clinically apparent or culture-positive middle ear disease. The lack of virulence was confirmed by the failure to develop middle ear disease following direct intrabullar challenge as well as with 2 additional 33F isolates. Functional genomic comparison against OM producing strains as well as ~50 invasive strains revealed that all three 33F strains lack the pneumococcal serine-rich repeat protein (PsrP) pathogenicity island. The PsrP island appeared to be present in the sequenced IPD strains.
Conclusion: Serotype 33F failed to produce EOM using either NP colonization and barotrauma or direct inoculation. Comparative genomic analysis revealed the absence of the PsrP pathogenicity island in these strains. PsrP is a representative of serine-rich repeat proteins found in many pathogenic streptococci and Staphylococcus aureus. Although non-essential for survival, it plays an important role in the formation of biofilms and adhesion to host cells. Further characterization of the function of this island in S. pneumoniae is necessary to define its role in virulence both for middle ear infection as well as invasive disease and pneumonia.
N. J. Croucher, None
S. I. Pelton, None
V. Sabharwal, None