Capacity of serotype 19A and 15B/C Streptococcus pneumoniae isolates for experimental otitis media: implications for the conjugate vaccine

Laufer, Alison S.; Thomas, Jonathan C.; Figueira, Marisol; Gent, Janneane F.; Pelton, Stephen I.; Pettigrew, Melinda M.

Non-vaccine Streptococcus pneumoniae serotypes are increasingly associated with disease. We evaluated isolates of the same sequence type (ST199) but different serotype (15B/C, 19A) for growth in vitro, and pathogenic potential in a chinchilla otitis media model. We also developed a qPCR assay to quantitatively assess each isolate, circumventing the need for selectable markers. In vitro studies showed faster growth of serotype 19A over 15B/C. Both were equally capable of colonization and middle ear infection in this model. Serotype 19A is included in new conjugate vaccine formulations while serotype 15B/C is not. Non-capsular vaccine targets will be important in disease prevention efforts.