Cellular Morphology and 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 colonies of M. catarrhalis 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 degrees Celsius for 24 hours. Cultures of the M. catarrhalis bacterium revealed gray-white hemispheric colonies about 1 millimeter 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. This is a test in which a wooden stick is used to try and push the colonies across the agar plate. The M. catarrhalis colonies scored positively on this test, which means that the colonies could be slid across the plate. The colonies did not demonstrate hemolysis, and were not able to ferment glucose, sucrose, maltose, and lactose. They were able to produce DNase. Cultures of the M. catarrhalis tested positive for oxidase 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 M. catarrhalis from a culture.
The recognition of M. catarrhalis as a pathogenic bacterium has led to studies for possible antibodies against it, which have led to a wider understanding of the composition of M. catarrhalis. A study by Merja Helminen and her colleagues revealed that the outer membrane protein (OMP) profiles of different strains of M. catarrhalis are extremely similar to each other. Analyses of these outer membrane protein profiles with monoclonal antibodies (MAbs) revealed that a few proteins with similar molecular masses in the different strains of M. catarrhalis have cross-reactive epitopes. Their experiments also identified a surface-exposed protein on M. catarrhalis that has an unusually high molecular mass. There has been a report that an 80kDa outer membrane protein on M. catarrhalis is immunogenic and common to all nonencapsulated strands of M. catarrhalis, which suggests that it may be used as an antigen for immunization.
Read more about this topic: Moraxella Catarrhalis
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