Immunization with Haemophilus influenzae type B (Hib) conjugate vaccine has prevented oropharyngeal colonization. It would be of interest to determine whether pneumococcal antibody can similarly prevent acquisition of SP. To determine whether BPIG, which is enriched in antibodies to SP polysaccharide, could prevent SP nasal colonization in the infant rat, we developed an intranasal challenge model with vaccine-type SP. In our previous studies, 10μL of 0.5% low-gelling-point agarose containing 2×105 cfu of SP was placed onto the nares of infant rats and reliably produced persistent colonization with SP serotypes 3, 4, 6 and 19.Methods: We randomized 4 day old Sprague-Dawley infant rats to one of 3 groups:1)low dose subcutaneous (SC) BPIG (10μg), 2)high dose SC BPIG(50 μg), or 3)equal volume of SC normal saline solution. One day later, all animals received intranasal challenge with 2 × 105 cfu SP serotype 3 in 0.5% agarose. Nasal aspirate (NA) were then obtained from all animals on day 2 and day 6 following nasal inoculation. Mean serum anti-SP IgG concentrations were measured just prior to nasal inoculation.Results: Mean serum anti-SP IgG concentrations in the low and high dose SC BPIG groups were approximately 2μg/mL and 10μg/mL, respectively.(+NA indicates a positive nasal aspirate for SP)Table With high challenge doses of SP, subcutaneous BPIG did not prevent nasal colonization in infant rats. Ongoing studies are evaluating whether vaccine-induced antibodies to SP polysaccharide will prevent nasal acquisition and carriage of SP after lower challenge inocula that more closely reflect human exposures. Conclusion: We describe a model of SP colonization of infants rats which may be useful for the evaluation of mucosal or systemic vaccines or therapeutic agents against SP.

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