Requirement for Capsule in Colonization by Streptococcus pneumoniae

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Abstract
Nasopharyngeal colonization is a necessary first step in the pathogenesis of Streptococcus pneumoniae. Using isolates containing defined mutations in the S. pneumoniaecapsule locus, we found that expression of the capsular polysaccharide is essential for colonization by the type 2 strain D39 and the type 3 strains A66 and WU2. Nonencapsulated derivatives of each of these strains were unable to colonize BALB/cByJ mice. Similarly, type 3 mutants that produced S. pneumoniae and show that isolates producing reduced levels of capsule can remain highly virulent.