Gram-positive cocci are often isolated from clinical samples. It is important to be able to distinguish these organisms from one another because while some are normal flora, others can be pathogenic.

This is in contrast to Streptococcus species, whose growth is selected against by this high salt ... The selective ingredients are the bile salts and the dye, crystal violet which inhibit the growth ...

"Normal flora" include Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, and anaerobes such as Bacteroides species, anaerobic gram-positive cocci, and Fusobacterium species.