Which test can provide a presumptive identification of Moraxella catarrhalis?

The beta-lactamase test is a valuable tool for the presumptive identification of Moraxella catarrhalis because this organism is known to produce beta-lactamase, an enzyme that provides resistance to certain antibiotics, particularly penicillins. When conducting this test, the presence of beta-lactamase indicates that the organism is capable of hydrolyzing the beta-lactam ring structure of antibiotics, which would be characteristic of Moraxella catarrhalis. This resistance is a key feature that helps differentiate it from other species that do not produce this enzyme.

In the context of the other tests mentioned, the coagulase test is used primarily to differentiate Staphylococcus aureus from other staphylococci and is not relevant for Moraxella catarrhalis. The oxidase test can determine the presence of cytochrome oxidase activity, which is useful for differentiating certain genera but is not specific for Moraxella catarrhalis. The Gram stain provides information about the morphology of the bacteria (it is a Gram-negative diplococcus), but by itself cannot confirm identification because many other bacteria share similar characteristics. Therefore, the beta-lactamase test is the most definitive choice for presumptive identification