an important pathogenic microbe, development of a possible antibiotic has been ongoing. A fraction of M. catarrhalis strains seemed to be resistant to ampicillin, which makes ampicillin and amoxicillin inappropriate choices of antibiotic against it. Although all strains of M. catarrhalis were susceptible to cotrimoxazole, erythromycin, sulfadimidine, and tetracycline, they were also resistant to trimethoprim. M. catarrhalis resistance to beta-lactam antibiotics, such as ampicillin and amoxicillin, is mediated by periplasmic lipoprotein beta-lactamases BRO-1 and BRO-2, which protect the peptidoglycan layer by hydrolyzing the beta-lactam molecules that enter the bacterial cell. The beta-lactamases are produced in the cytoplasm and translocated to the periplasmic space by twin-arginine translocation pathway, which is a protein secretion pathway that transports proteins across a bilipid membrane in a folded state. M. catarrhalis produces and secretes beta-lactamase containing outer-membrane vesicles that can function as an extracellular delivery system of beta-lactam resistance that promotes the survival of otherwise beta-lactam sensitive bacteria in the vicinity of M. catarrhalis. This behavior is beneficial for the other bacteria and can make the antibiotic treatment of polymicrobial infections more difficult. Also, the resistance of M. catarrhalis to other antibiotics may be attributed to beta-lactamase, as well, because the use of these antibiotics has triggered an increase in development of beta-lactamase, which resists antibiotics. However, a 1994 study has identified a large protein on the surface of M. catarrhalis that may serve as a target for protective antibodies. This UspA (the designated antigen) protein is the first surface-exposed protein on M. catarrhalis that can be a target for biologically active antibodies, and therefore lead to a vaccination. This protein was also present in all of the strains tested. The large size of the exposed protein macromolecule makes it similar to Neisseria gonorrhoeae outer membrane protein macromolecular complex, which implies that UspA may be a single polypeptide chain. Active immunization, in a study, of M. catarrhalis in the respiratory tract allowed the control of the growth of M. catarrhalis and led to the development of serum antigens. Also, an enhanced ability exists in the test subjects (mice) to clear M. catarrhalis from their lungs. Likewise, passive immunization of M. catarrhalis from the mice respiratory tracts also enhanced the mice's ability to clear the microbes from their lungs, which means that serum antibodies likely play a large role in the immunization and protection of the respiratory tract. Along with outer membrane proteins that are consistent