Which of the following bacteria is classified as gram positive cocci?

Staphylococcus aureus is classified as a gram-positive cocci bacterium due to its spherical shape and its reaction to the Gram stain. When subjected to the Gram staining procedure, Staphylococcus aureus retains the crystal violet dye, appearing purple under the microscope. This characteristic is indicative of a thick peptidoglycan layer in its cell wall, which is typical of gram-positive bacteria.

In contrast, the other options are classified differently. Escherichia coli and Salmonella enterica are gram-negative bacilli, which means they have a thinner peptidoglycan layer and an outer membrane that does not retain the crystal violet dye during the staining process. Bacillus cereus, while it is a gram-positive bacterium, is rod-shaped (bacillus) rather than cocci (spherical). Therefore, it does not fit the criteria for this specific classification as it relates to shape. The unique characteristics of Staphylococcus aureus make it the clear choice as the gram-positive cocci.