Using the catalase test, a streptococcus sample would be:
a. gram (+), catalase (+)
b. gram catalase (+)
c. gram catalase
d. gram (+), catalase

The correct answer would be option D: Gram (+) and Catalase (-).

Explanation:

Streptococcus bacteria have a cellular wall made up of various layers of peptidoglycan which is a macromolecule composed of amino acids and sugars that are assembled as if woven together, therefore they are Gram (+) bacteria.

The Catalase test is used to determine if a bacteria has the ability to produce the Catalase enzyme, the principle of the test is, when the bacteria comes into contact with hydrogen peroxide, if it is Catalase (+) then oxygen bubbles will appear, since the bacteria is able to break down hydrogen peroxide into oxygen and water, and if the bacteria is Catalase (-) then, nothing will happen.

In this case, Streptococcus bacteria are not able to produce the Catalase enzyme, therefore, they are Catalase (-).

Answers A, B and C are incorrect because they have the wrong combinations of a results, in answer A: Streptococcus bacteria are Gram (+) but Catalase (-), in answer B: Streptococcus bacteria are neither Gram (-) or Catalase (+), and in answer C: Streptococcus bacteria are Catalase (-) but are not Gram (-).