Nonencapsulated Streptococcus pneumoniae Cause Acute Otitis Media in the Chinchilla That Is Enhanced by Pneumococcal Surface Protein K.
BACKGROUND
Use of the pneumococcal conjugate vaccine has led to serotype replacement of carriage and acute otitis media (AOM) pneumococcal isolates. Increases in nonencapsulated Streptococcus pneumoniae (NESp) isolates have also occurred, and there are increasing reports of NESp-associated disease. Disease prevalence and virulence factors of NESp isolates have not been studied.


METHODS
A chinchilla model of pneumococcal AOM was utilized, and disease was assessed through bacterial enumeration along with scoring visible signs of pathology. An adhesion-invasion assay using a human epithelial cell line was performed.


RESULTS
Nonencapsulated Streptococcus pneumoniae strains containing pneumococcal surface protein K (PspK) were more likely to cause AOM and pathology upon infection. Deletion of PspK from an isolate significantly reduced bacterial loads. Increased epithelial cell adhesion correlated with increased virulence of NESp isolates naturally lacking PspK. Furthermore, expression of PspK by an avirulent NESp resulted in virulence.


CONCLUSIONS
The presence of PspK increased the disease potential of NESp. Pneumococcal surface protein K is not the only virulence factor of NESp in AOM. Expression of PspK in an avirulent NESp mediated the progression to pneumococcal disease. Genetic exchange between pneumococci may allow dissemination of PspK, increasing the potential of NESp disease. The current study is the first report of a NESp-specific virulence factor.
Departments of Microbiology.
Lance E
LE
Keller
Departments of Microbiology.
Jessica
J
Friley
Departments of Microbiology.
Cheshil
C
Dixit
Departments of Pathology ; Microbiology , University of Alabama at Birmingham.
Moon H
MH
Nahm
Departments of Microbiology ; Surgery ; Division of Infectious Diseases , University of Mississippi Medical Center, Jackson, Mississippi.
Larry S
LS
McDaniel
AOM; NESp; PspK; acute otitis media; nonencapsulated Streptococcus pneumoniae; pneumococcal surface protein K