The identification of MreB as essential for bacterial chromosome segregation provides a new target for antibiotic action. The MreB function is useful in the development of screening assays for new antibiotics, which may use, for example, genetic mutants in MreB, tests of MreB mediated chromosome segregation, and the like. In one embodiment of the invention, the antibiotic is an isothiourea compound, which may comprise a polyhalogenated benzyl group, e.g. at the 4 position, the 2,4 position, etc. A pharmaceutical composition comprising an MreB targeted antibiotic as an active agent is administered to a patient suffering from a microbial infection, particularly bacterial infections.