The infant rat as a model of bacterial meningitis.

The pathogenesis of bacterial meningitis was studied in infant rats. Intranasal intoculation of greater than 10(3) Haemophilus influenzae type b resulted in an incidence of bacteremia that was directly related to the size of hte challenge inoculum. The temporal and quantitative relationship of bacteremia to meningitis indicated that bacteria spread to the meninges by the hematogenous route and that the magnitude of bacteremia was a primary determinant in the development of meningitis. In a sparate series of experiments, infant rats that were fed Escherichia coli strain C94 (O7:K1:H-) became colonized and developed bacteremia and meningitis, but invasive disease was rare when rats were fed E. Coli strain Easter (O75:K100:H5). A comparison of intranasal vs. oral challenge indicated that the nasopharynx was the most effective route for inducing H. influenzae bacteremia, whereas the gastrointestinal route was the more effective challenge route for the E. coli K1 serotype.