Myristoylation negative msbB-mutants of probiotic E. coli Nissle 1917 retain tumor specific colonization properties but show less side effects in immunocompetent mice.

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.