Which of the following is NOT a gram negative cocci?

Staphylococcus aureus is the correct answer because it is classified as a gram-positive cocci. This means that when subjected to the Gram stain procedure, it retains the crystal violet dye, appearing purple under a microscope due to its thick peptidoglycan layer. In contrast, the other choices listed are examples of gram-negative cocci.

Moraxella and Neisseria species, including Neisseria meningitidis, are typically identified as gram-negative cocci because they do not retain the crystal violet stain and instead take up the counterstain, appearing pink. This characteristic is critical in microbiology for identifying and differentiating types of bacteria based on their cell wall structure. Understanding these classifications helps in diagnosing infections and determining appropriate antibiotic treatments.