Enhanced Susceptibility of Mice Infected with Murine Cytomegalovirus to Intranasal Challenge with Escherichia coli: Pathogenesis and Altered Inflammatory Response
Three-week-old mice inoculated intraperitoneally with murine cytomegalovirus (MCMV) and then challenged intranasally with Escherichia coli strain K1 demonstrated enhanced mortality (70%-90%) as compared with control animals infected with either pathogen alone (0-20%, P < 0.05). Mortality was greatest when animals were challenged with E. coli on days 1 or 3 after MCMV inoculation. On day 3 of infection with MCMV, clearance of E. coli from blood and tissues was impaired, and there was a decreased inflammatory response to an E. coli-inoculated sponge implanted subcutaneously (geometric mean of 830 leukocytes in sponge fluid/mm3 in MCMV-infected animals vs. 8,510 Ieukocytes/mm3 in controls, P < 0.01). On days 1 and 3 of MCMV infection, decreased leukocyte counts in sponge fluid correlated with increased levels of bacteremia (P < 0.05). These results indicate that MCMV enhances susceptibility to an intranasal challenge with E. coli. A decrease in the inflammatory response may be one mechanism by which MCMV increases susceptibility to bacterial infections.