ASCP Technologist in Microbiology (M) Practice Exam – Prep Guide & Study Questions 2026

Moraxella catarrhalis possesses the unique feature of producing DNase, which is a critical characteristic for its identification in laboratory settings. DNase acts on DNA, breaking it down into smaller fragments, and this enzymatic activity is often detected in culture media. The presence of DNase can be demonstrated by incorporating DNA into the medium, where a clear zone of hydrolysis around the colony indicates DNase activity. This characteristic is particularly useful for differentiating Moraxella catarrhalis from other organisms that may appear similar in morphology, especially members of the Neisseria genus, which do not produce DNase.

Other features listed in the choices do not uniquely aid in the identification of Moraxella catarrhalis. For example, clear colonies on sorbitol MacConkey agar typically refer to Escherichia coli O157:H7, which is not relevant to Moraxella. Swarming growth on sheep blood agar (SBA) is a characteristic associated with certain species of Proteus, and bright red pigment production does not pertain to Moraxella catarrhalis as it is not known for producing such pigments. Thus, the ability to produce DNase is a distinct and key feature leveraged in the laboratory for recognizing