This invention relates to a strain of Moraxella catarrhalis containing a gene mutation that prevents endotoxic lipooligosaccharide (LOS) synthesis and potential use of the mutant for developing novel vaccines against the pathogen, for which there is currently no licensed vaccine. M. catarrhalis is one of the causative agents of otitis media (middle ear infection), sinusitis, and lung infections. The mutant is defective in the lpxA gene, whose enzyme product is relevant in lipid A biosynthesis (lipid A is part of the LOS). The nontoxic mutant was found to elicit high levels of antibodies with bactericidal activity and provided protection against wild type bacterial challenge. Use of this mutant bacterium is envisioned as a new approach for vaccines against M. catarrhalis.