Anticapsular polysaccharide antibodies and nasopharyngeal colonization with Streptococcus pneumoniae in infant rats

Abstract

To evaluate the effect of passive immunization with anticapsular antibodies on nasopharyngeal carriage, two models of Streptococcus pneumoniae colonization were developed in infant rats. In a direct inoculation model, 3- to 4-day-old infant rats were intranasally inoculated with 2 x 105 cfu of S. pneumoniae type 3 or 6 x 103 cfu of S. pneumoniae type 23F. In an intralitter transmission model, 2 infant rats were intranasally inoculated with 103 cfu of pneumococcus type 3 or type 19F and placed in a cage containing 10 infant rats. Pretreatment with bacterial polysaccharide immune globulin led to a significant reduction in colonization of contact animals with S. pneumoniae type 3 or 19F in the intralitter transmission model (P < .05). No effect of immune globulin could be demonstrated in the direct inoculation model. These results indicate that systemic anticapsular antibodies conferred significant protection against nasopharyngeal acquisition by intralitter spread of S. pneumoniae type 3 and 19F.