among different strains of M. catarrhalis, a sort of subclass-specific IgG antibody response to certain outer membrane proteins may also exist. Therefore, the outer membrane antigens of M. catarrhalis also provide a possible vaccine source. Also, a bactericidal serum antibody has also been developed in response to the diseases caused by M. catarrhalis. Treatment Treatment options include antibiotic therapy or a so-called "watchful waiting" approach. The great majority of clinical isolates of this organism produce beta-lactamases, so are resistant to penicillin. Resistance to trimethoprim, trimethoprim-sulfamethoxazole (TMP-SMX), clindamycin, and tetracycline have been reported. It is susceptible to fluoroquinolones, most second- and third-generation cephalosporins, erythromycin, and amoxicillin-clavulanate. Vaccine development Currently, no vaccine is known in the US against M. catarrhalis infection. It is a significant cause of respiratory tract infections against which a vaccine is sought. Several outer membrane proteins are currently under investigation as potential vaccine antigens, including the porin M35. Biochemistry During the first reported case of M. catarrhalis causing bacteremia that was associated with septic arthritis, the microbe was cultured, which revealed much about the morphology of its colonies, as well as M. catarrhalis itself. M. catarrhalis is a large, kidney-shaped, Gram-negative diplococcus. It can be cultured on blood and chocolate agar plates after an aerobic incubation at 37 °C for 24 hours. Cultures revealed gray-white hemispheric colonies about 1 mm in diameter. These colonies were fragile and easy to crumble, and appeared to have a waxy surface. The hockey puck test was applied to these M. catarrhalis colonies, in which a wooden stick is used to try to push the colonies across the plate. The M. catarrhalis colonies scored positively on this test, which means they could be slid across the plate. The colonies did not demonstrate hemolysis, and were not able to ferment glucose, sucrose, maltose, or lactose. They were able to produce DNase. Cultures of the M. catarrhalis tested positive for oxidase, lipase, and nitrate reduction, which is characteristic of M. catarrhalis. Many laboratories also perform a butyrate esterase test and a beta-lactamase test. Both tests should be positive and can help to rapidly identify it from a culture. The recognition of M. catarrhalis as a pathogen has led to studies for possible antibodies against it, which have led to a wider understanding of its composition. The outer membrane protein (OMP) profiles of different strains of M. catarrhalis are extremely similar to each other. Analyses of