Abstract
Specific colonization of solid tumors by bacteria opens the way to novel approaches in both tumor diagnosis and therapy. However, even non-pathogenic bacteria induce responses by the immune system, which could be devastating for a tumor bearing patient. As such effects are caused e.g., by the lipid A moiety of the lipopolysaccharide, a msbB-mutant of the probiotic E. coli Nissle 1917 strain was investigated. Bacteria of the mutant strain did not show any growth defects in culture media when compared to wild-type E. coli Nissle 1917 but were unable to myristoylate lipid A, had less toxic effects on immunocompetent BALB/c mice, and were still able to specifically colonize tumors. Therefore, the modification of lipid A could result in bacterial strains that might be better suited for diagnosis and therapy of tumors than the corresponding wild-type strains, even if those are not considered pathogenic or are of probiotic background.