• Gram-positive cocci can first be categorized as catalase positive or catalase negative.
  — Catalase-positive cocci include species of Staphylococcus.
  — Catalase-negative cocci include species of Streptococcusand Enterococcus.

Catalase-positive cocci: Staphylococcus

• Species of Staphylococcus can be categorized based on the presence of coagulase, which is a bacterial enzyme that induces blood or plasma coagulation:
  — The coagulase-positive group comprises Staphylococcus aureus.
  — Coagulase-negative species include Staphylococcus epidermidis and Staphylococcus saphrophyticus.

Staphylococcus aureus

• Named for its golden color.
• Some strains are resistant to the antibiotic Methicillin (these strains are called MRSA); infections caused by these strains are difficult to treat.
• Inflammatory Conditions caused by S. aureus
  — Skin infections include various purulent conditions such as impetigo, furuncles, and others.
  — Serious organ infections include endocarditis, pneumonia, and infections of the bones and joints that lead to osteomyelitis and septic arthritis.

• Toxin-mediated conditions caused by S. aureus
• Toxic shock syndrome
  — Formerly associated with tampon use, septic shock now occurs at least as often, if not more often, in non-menstruating individuals.
  — Toxic shock syndrome is characterized by acute onset of fever, gastrointestinal upset, sore throat, and diffuse erythroderma; desquamation occurs when the skin begins to peel and flake away.
• Scalded skin syndrome* is also a desquamating condition, is most common in infants and young children.
  — In our illustration, we’ve shown the characteristic red and flaky areas of skin.
• Food Poisoning

Staphylococcus epidermis

• An important source of medical device infections, particularly in individuals with prosthetic joints and valves or catheters and shunts; it is a significant cause of bacterial sepsis.

Staphylococcus saphrophyticus

• Common cause of urinary tract infections.

Catalase-negative cocci: Streptococci & Enterococci

• Hemolysis can be used to distinguish between species that are alpha-hemolytic, beta-hemolytic, and gamma-hemolytic.

Alpha-hemolytic strains
Can be further distinguished by their sensitivity to optochin:

• Streptococcus pneumoniae is sensitive to optochin, whereas Viridans group Streptococci are not.
  — Streptococcus pneumoniae is associated with pneumonia, otitis media and sinusitis, as well as meningitis.
  — Viridans group Streptococci are associated with subacute endocarditis and dental caries, as well as some other infections not listed here.

Beta-hemolytic strains
Can be distinguished by their sensitivity to Bacitracin:

• Group A Streptococcus is sensitive, whereas Group B streptococcus is not.
  — Group A Streptococcus, also known as Streptococcus pyogenes, causes pharyngitis with white exudate in the tonsils (strep throat); some people will also develop a rash over their bodies, called Scarlet fever.
  — Group A Streptococcus is also responsible for a variety of soft tissue infections, which can range from impetigo and erysipelas to the more serious cellulitis or even necrotizing fasciitis.
  — Group A streptococcus can cause toxic shock syndrome.
  — Delayed, anti-body mediated reaction to Group A Streptococcus infection can occur in some patients, and may produce post-streptococcal glomerulonephritis or rheumatic fever.
  — Group B Streptococcus, also called Streptococcus agalactiae, is associated with neonatal infections including meningitis, pneumonia, and bacteremia; because the neonates acquire the bacteria from their mothers, prenatal care should include screening for Group B Streptococcus. Post-pregnancy infections can also have serious consequences for the mother.
  — Adult infections can manifest similarly, including bacteremia, pneumonia, and bone, joint, and soft tissue infections.

Gamma-hemolytic strains
Strains that can grow in relatively high concentrations of salt and bile are categorized as Enterococcus
— These bacteria were formerly categorized as Group D Streptococcus, and are common commensals of the GI tract.

• Of particular concern are strains resistant to Vancomycin.
• Enterococci are a significant cause of nosocomial infections.
• Enterococci are commonly associated with urinary tract infections, as well as endocarditis, peritonitis, and bacteremia.
• Streptococcus bovis, which is also gamma-hemolytic but cannot thrive in high salt concentrations, causes similar illnesses as Enterococcus, and is also associated with colorectal cancer.