Serratia marcescens is classified as which type of organism by DNase results?

Serratia marcescens is classified as a Gram-negative organism based on its cell wall structure and staining characteristics. In the Gram stain procedure, the bacteria retain the crystal violet stain poorly, allowing the counterstain (usually safranin) to be visible, which gives the bacteria a pink appearance under the microscope.

In addition to its classification as Gram-negative, Serratia marcescens exhibits certain biochemical activities, including the production of DNase. This enzyme is involved in the degradation of DNA, which is a characteristic feature of some bacterial species, particularly within the Enterobacteriaceae family, to which Serratia belongs.

While the other classifications provided in the options pertain to different characteristics of bacteria (like aerobic and anaerobic respiration), they do not accurately pertain to Serratia marcescens as a Gram-negative organism, which is fundamentally defined by its cell wall structure and reaction to Gram staining. Thus, identifying Serratia marcescens as a Gram-negative organism aligns with standard microbiological classification practices.