Our preliminary studies suggested that infant rats exposed to SP via the intranasal route develop persistent nasal colonization with SP. In these experiments, 10μL of 0.5% low-gelling-point agarose containing approximately 2×105 SP serotypes 3, 4, 6 or 19 were placed onto the nares of infant rats (n=12 for each group). All pups became colonized with SP, without bacteremia. To develop this intranasal model of SP colonization further and attempt to induce invasive pneumococcal disease, 4 day old Sprague-Dawley infant rats received an intranasal inoculation of 2 × 105cfu SP serotype 3 in 10μL of 0.5% agarose. Six days following intranasal challenge, animals were randomized to either intrapulmonary injection of 0.025 ml of 0.5% agarose to produce lung injury or to no injection. Nasal aspirates (NA) and blood cultures (BCx) were monitored for SP just prior to the intrapulmonary injection (Day 6) and daily thereafter for three days (Days 7-9). (+NA and +BCx indicate positive nasal aspirates and blood cultures for SP, respectively): Table Two animals with bacteremia after lung puncture died one day after the bacteremia was detected. We conclude that: 1)this intranasal inoculation model produces reliable and persistent SP nasal colonization in the infant rat and 2)intranasal colonization followed by intrapulmonary puncture with agarose resulted in pneumococcal bacteremia and death in 20% of animals. Therefore, intranasal inoculation with SP serotype 3 together with intrapulmonary injection of agarose may become a suitable model of invasive pneumococcal disease following SP colonization in the infant rat.

Table 1
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