Methods: Three day old C57B/6 mice were infected with E. coli by intranasal or oral route. Animals were sacrificed at 24 or 48 hours and organs were collected. Cross sections of brains were stained with Gap43 antibody to demarcate neural tissue and FluoroMyelin stains and NFKβ antibodies to identify regions of immune activation. Bacteria were identified by fluorescence in situ hybridization (FISH) using ribosomal probes. To model post-delivery prevention of infection, intranasal ciprofloxacin was given 30 minutes after the inoculation in an attempt to abrogate the brain infection.
Results: Intranasal and oral inoculation with E. coli resulted in similar gut colonization. However, intranasal inoculation of E. coli resulted in a significantly higher rate of CNS infection (80% vs. 22%,p <0.001). Colony forming units (CFUs) in whole brain specimen were significantly higher after intranasal infection compared to oral infection (626 vs. 510 respectively, p= 0.0015). Liver, spleen and blood did not differ in CFU with either route of infection. Overt morbidity or mortality were not observed. Microscopic examination showed E. coli within the olfactory nerve only following intranasal inoculation. Intranasal infected animals had markedly less myelin staining compared to orally infected and uninfected controls. Intranasal treatment with ciprofloxacin abrogated CNS infection.
Conclusion: E. coli efficiently infects the neonatal CNS by tracking along the olfactory nerve and results in NFKβ activation and reduced myelination. Single dose intranasal treatment with ciprofloxacin abrogates infection. Ongoing studies will determine the long term effect of ascending olfactory infection on motor and behavioral development.
Y. Tang, None
P. Seed, None