According to Todar's Online Textbook of Bacteriology, Gram-positive cocci bacteria are responsible for one-third of all bacterial infections in humans. These infections include strep throat, pneumonia, food poisoning, otitis media, various skin diseases, meningitis and severe types of septic shock. Additionally, Gram-negative cocci bacteria are responsible for causing gonorrhea and meningococcal meningitis.
Cocci bacteria are spherical in shape and include Gram-positive bacteria Staphylococcus aureus, Streptococcus pyogenes and Streptococcus pneumoniae, according to Todar's Online Textbook of Bacteriology. Gram-negative cocci bacteria include Neisseria gonorrhoeae and N. meningitidis.
Staphylococcus aureus is most commonly found in the nasal membranes, skin and GI tract of humans, according to Todar's Online Textbook of Bacteriology. It is the most likely to cause disease and is considered a pathogen. Because it is resistant to penicillin and lives on otherwise healthy individuals, it is easily transmitted to others. Streptococcus pyogenes is the bacteria responsible for strep throat, scarlet fever and tonsillitis. Streptococcus pneumoniae causes bacterial pneumonia as well as infections of the middle ear and meningitis.
Neisseriaceae, a Gram-negative bacteria family, has many strains that help make up the normal flora found in the respiratory tract and throat of humans, according to Todar's Online Textbook of Bacteriology. However, the Neisseria gonorrhoeae causes bacterial gonorrhea, and Neisseria meningitidis causes a severe form of bacterial meningitis that is responsible for epidemics of the disease.