Differentiating Staphylococcus from Streptococcus

Staphylococcus species

Staphylococcus are pathogens of humans and other mammals. Traditionally they were divided into two groups on the basis of their ability to clot blood plasma (the coagulase reaction). The coagulase-positive staphylococci constitute the most pathogenic species S. aureus. The coagulase-negative staphylococci (CNS) are now known to comprise over 30 other species. The CNS are common commensals of skin, although some species can cause infections. It is now obvious that the division of staphylococci into coagulase positive and negative is artificial and indeed, misleading in some cases. Coagulase is a marker for S. aureus but there is no direct evidence that it is a virulence factor. Also, some natural isolates of S. aureus are defective in coagulase. Nevertheless, the term is still in widespread use among clinical microbiologists.

Streptococcus species

Streptococcus is a group of spheroidal bacteria belonging to the family Streptococcaceae. The term Streptococcus (“twisted berry”) refers to the bacteria’s characteristic grouping in chains that resemble a string of beads. Streptococci are microbiologically characterized as gram-positive and nonmotile.

Streptococcus contains a variety of species, some of which cause disease in humans and animals, while others are important in the manufacture of certain fermented products. Streptococcus pyogenes, often referred to as group A streptococcus bacteria, can cause rheumatic fever, impetigo, scarlet fever, puerperal fever, streptococcal toxic shock syndrome, strep throat, tonsillitis, and other upper respiratory infections. Necrotizing fasciitis, a rapidly spreading infection of the skin and underlying tissue caused by S. pyogenes, has been popularly referred to as the “flesh-eating disease.” Streptococcus agalactiae, or group B streptococcus bacteria, can cause infections of the bladder and uterus in pregnant women; in newborn infants infection with the bacterium may result in sepsis (blood poisoning), meningitis (inflammation of the membranes covering the brain and spinal cord), or pneumonia. Streptococcus pneumoniae, also called pneumococcus, is an important human pathogen that causes pneumonia, sinusitis, otitis media, and meningitis. Fecal (enterococcal) species occur in great numbers in the bowel and can cause urinary tract infections and endocarditis. S. mutans, belonging to the viridans species, inhabits the mouth and contributes to tooth decay. Among the lactic species, S. lactis and S. cremoris are used in commercial starters for the production of butter, cultured buttermilk, and certain cheeses. Streptococci generally are classified by the type of carbohydrate contained in the cell wall, a system called the Lancefield classification.