797 PROTECTION AGAINST HEMOPHILUS INFLUENZAE (HITB) MENINGITIS RESULTING FROM FEEDING OF E. COLI 075: K100: H5 (E.C. 89)

Abstract

Serum antibody to HITB capsular polysaccaride (ACAB) has been induced by gastrointestinal colonization with genetically unrelated bacteria possessing cross-reactive antigen (CRA). To investigate whether immunization with CRA results in altered susceptability to HITB meningitis, rats aged 5 days were fed either 10⁷ E.C. 89 or saline (controls) on 3 successive days. All rats thrived normally. Stool cultures from 95% of 76 E.C. 89-fed rats yielded bacteria with CRA for ≥ 7 days, and 42% for 35 days; none of 68 controls were thus colonized. When aged 42 days, all rats were inoculated intransally with 10⁷ HITB. After 5 days comparison of blood and CSF cultures showed a significantly (p<0.05) decreased incidence of bacteremia (41% vs. 62%) and meningitis (7% vs. 20%) in E.C. 89-fed rats. Pre-challenge serum levels of ACAB were undetectable (<20 ng/ml.) in both E.C. 89-fed and control rats. Five days after HITB challenge ≥200 ng/ml ACAB was detected in 32/46 E.C. 89-fed rats compared to 19/44 control rats (p<0.01). Levels of ACAB correlated with protection against bacteremia and meningitis; rats with meningitis had ACAB levels < 30 ng/ml. These data are consistent with priming of ACAB following colonization with E.C. 89 and extends previous observations to include protection against meningitis in a model in which the evolution of invasive HITB infection simulates that occurring in humans.

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