Abstract
Vaccines targeting Streptococcus pneumoniae (Spn) are limited by dependence on capsular polysaccharide and its serotype diversity. More broadly-based approaches using common protein antigens have not resulted in a licensed vaccine. Herein, we used an unbiased, genome-wide approach to find novel vaccine antigens to disrupt carriage modeled in mice. A Tn-Seq screen identified 198 genes required for colonization of which 16 are known to express conserved, immunogenic surface proteins. After testing defined mutants for impaired colonization of infant and adult mice, 5 validated candidates (StkP, PenA/Pbp2a, PgdA, HtrA, and LytD/Pce/CbpE) were used as immunogens. Despite induction of antibody recognizing the Spn cell surface, there was no protection against Spn colonization. There was, however, protection against an unencapsulated Spn mutant. This result correlated with increased antibody binding to the bacterial surface in the absence of capsule. Our findings demonstrate how the pneumococcal capsule interferes with mucosal protection by antibody to common protein targets.
Highlights
Streptococcus pneumoniae (Spn, the pneumococcus) is a common member of the human upper respiratory tract (URT) flora, found in 25–65% of children and
S. pneumoniae strains were grown in tryptic soy (TS) broth (BD, Franklin Lakes, NJ) at 37 °C, without aeration, to an optical density at 620 nm (OD620) of 1.0; or incubated on TS agar plates supplemented with 100 μl of catalase (30,000 U/ml; Worthington Biochemical) and antibiotic at 37 °C in 5% CO2, overnight
Protein concentration was assessed by Bradford protein assay (Bio-Rad cat. no. 5000006; bovine serum albumin Protein Standard II cat. no. 5000007)
Summary
Streptococcus pneumoniae (Spn, the pneumococcus) is a common member of the human upper respiratory tract (URT) flora, found in 25–65% of children and 98 pneumococcal capsular polysaccharide (CPS)
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