Final answer:
Lab diagnosis of Moraxella catarrhalis involves microscopic examination, culture on chocolate agar, oxidase positive testing, and sugar utilization tests, followed by antimicrobial susceptibility testing to guide treatment.
Step-by-step explanation:
In the lab diagnosis of Moraxella catarrhalis, microscopic examination of sputum or bronchoalveolar lavage samples typically reveals the presence of the bacteria. They are identified as gram-negative diplococci. The identification process may include culturing on agar that supports the growth of M. catarrhalis, such as chocolate agar, followed by oxidase testing, where the bacteria will test positive. Additionally, sugar utilization tests can be performed where M. catarrhalis would exhibit positive glucose oxidation but would not utilize lactose or sucrose.
Unlike other bacteria, M. catarrhalis may not present distinctive traits on agar media as some might do (like hemolysis on blood agar), so reliance on these biochemical and enzymatic tests is crucial for a definite diagnosis. Antimicrobial susceptibility testing (AST) is also typically conducted to inform treatment decisions.