Which genera are positive for phenylalanine deaminase?

The genera that are positive for phenylalanine deaminase include Morganella, Providencia, and Proteus. The test for phenylalanine deaminase is particularly significant in differentiating certain Enterobacteriaceae. These three genera are known to produce the enzyme phenylalanine deaminase, which catalyzes the conversion of phenylalanine to phenylpyruvic acid, leading to a color change when specific reagents are added during the testing process.

Morganella and Proteus, in particular, are often identified in clinical settings due to their association with urinary tract infections and other infections. Providencia also shares similar pathogenic characteristics and is included in this group. The ability to produce phenylalanine deaminase is an important biochemical marker that aids in the identification and differentiation of these organisms in microbiological studies.

The other genera listed in the choices either do not have this enzymatic activity or are not typically characterized by a positive phenylalanine deaminase test, making option B the correct selection.