Augmentation of host defence against bacterial and fungal infections of mice pretreated with the non-pathogenic Escherichia coli strain Nissle 1917.

Escherichia coli strain Nissle 1917 (DSM 6601, Mutaflor) was investigated for its ability to enhance the immune response against bacterial or fungal infections in vivo. Mice were infected intravenously with either 6 x 10(3) colony forming units (cfu) of Listeria monocytogenes bacteria or 5 x 10(5) Candida albicans cells. One day prior to infection, mice were treated orally with four different concentrations of E. coli strain Nissle 1917 (10(6), 10(7), 10(8), and 10(9) viable cells). Three days after infection with L. monocytogenes or one day after infection with C. albicans, mice were sacrificed and the parasite burden of the main target organs of the respective infection model were examined. The protective effect of E. coli strain Nissle 1917, compared to placebo-treated controls and to mice treated with a dose of 10(4). Units interferon gamma, is shown as the reduction of viable bacteria in spleen and liver or viable fungi in the kidneys of infected animals, respectively. Orally administered E. coli strain Nissle 1917 reduced Listeria monocyto-genes and Candida albicans in a dose-dependent manner. Treatment with 10(9) cfu of E. coli bacteria led to a reduction of Listeria counts to 7.4% in spleen and 2.4% in liver. A more than 10-fold decrease of viable Candida albicans (residual parasitaemia 6.8%) in the kidneys of the infected animals was also achieved by this E. coli concentration. These results suggest that E. coli strain Nissle 1917 is a potent immunostimulator of bacterial origin with highly protective efficacy against pathogenic bacterial of fungal infections.