Experimental meningococcal infection in mice: a model for mucosal invasion

A more complete understanding of meningococcal disease has been hampered by the lack of an appropriate animal model. Previous models have utilized injections of meningococci, which precludes the study of nasopharyngeal colonization and invasion. We have developed a model for meningococcal disease in which litters of 5-day-old mice are challenged intranasally with 10(7) viable meningococci. Bacteremia is monitored by jugular venous blood cultures, and cerebrospinal fluid is sampled by cisternal punctures. Human disease-associated and carrier strains were compared; nasopharyngeal colonization was similar for these bacteria, but the case-associated strains were much more frequently invasive and caused bacteremia. Twenty-one percent of bacteremic animals had meningitis. There was an age-related susceptibility to infection which correlated inversely with the levels of serum complement. Preinjection of iron dextran increased the number of animals which were bacteremic, the concentration of bacteria in blood, and nasopharyngeal colonization. Noncapsular variants of virulent meningococci did not colonize nasopharyngeal tissue in vivo, and they were not invasive. This neonatal mouse model mimics meningococcal disease as seen in humans and may be useful in studying the initial events in the pathogenesis of meningococcal disease.