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Gram-Positive Cocci - Overview
Overview of Gram-Positive Cocci
Catalase-positive cocci: Staphylococcus
Coagulase-Positive Staphylococcus
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
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
Coagulase-Negative Staphylococcus
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
Alpha-hemolytic strains
Optochin-Sensitive:
Streptococcus pneumoniae is associated with pneumonia, otitis media and sinusitis, as well as meningitis.
Optochin-Insensitive:
Viridans group Streptococci are associated with subacute endocarditis and dental caries, as well as some other infections not listed here.
Beta-hemolytic strains
Bacitracin-Sensitive:
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.
Bacitracin-Insensitive:
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.