Streptococcus.

Streptococcus is a genus of gram-positive cocci, or bacteria, with a thick peptidoglycan layer in their cell walls (gram-positive) that appear under the microscope as chains of two or more spherical cells (cocci). The streptococci can grow in low concentrations of oxygen or without oxygen and are distinguished from bacteria in the genus Staphylococcus in the laboratory by the production of the enzyme catalase by staph species.