Chapter Overview

Gram-positive and gram-negative cocci are significant causes of infections and disease in the community and clinical settings.
Members of the genus Staphylococcus are gram-positive cocci that commonly inhabit the human skin and mucous membranes yet are resistant enough to survive drying, heat, and other harsh environmental conditions.
Staphylococcus aureus, the most serious pathogen in the group, may be identified by its production of coagulase, hemolysis, and several types of virulence factors that aid its invasion and establishment in tissues.
Among the most notable staphylococcal skin infections are furuncles, carbuncles, and impetigo; important systemic infections are toxic shock syndrome, osteomyelitis, and scalded skin syndrome.
Streptococcus bacteria are gram-positive cocci in chains that are widespread in humans, animals, and the environment. Human species are commensals and pathogens of the skin, mucous membranes, and large intestine.
The primary pathogen is Streptococcus pyogenes (group A), which has a variety of virulence factors including surface antigens, toxins, and enzymes.
The primary diseases of group A include skin infections (pyoderma, erysipelas, and pharyngitis), and systemic infections (scarlet fever, rheumatic fever, and glomerulonephritis).
Other streptococcal diseases include subacute endocarditis, tooth abscesses, dental caries, streptococcal pneumonia, and otitis media (S. pneumoniae).
The Neisseria are gram-negative diplococci that reside in the mucous membranes of humans and animals.
Two major infectious agents are N. gonorrhoeae, the cause of gonorrhea, and N. meningitidis, the cause of one form of meningitis.
The pathogenicity of Neisseria comes from capsules, pili, and endotoxins.
Gonorrhea is a common STD that presents symptoms of urethritis, pelvic inflammatory disease, and ophthalmic inflammation.
Meningococcal meningitis invades the nasopharynx and spreads to the meninges, brain, spinal cord, and general circulation.
Control of infections by all cocci requires use of universal precautions, care in testing and selection of appropriate antimicrobial drugs, and in a few cases, vaccination.

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