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 Streptococc