What is the preferred method to differentiate Staphylococcus aureus from Staphylococcus epidermidis?

The preferred method to differentiate Staphylococcus aureus from Staphylococcus epidermidis is the coagulase test. This test specifically identifies the presence of coagulase, an enzyme produced by Staphylococcus aureus that causes fibrinogen in plasma to clot, forming a fibrin barrier around the bacteria. This clumping is a key characteristic that allows clinicians and microbiologists to differentiate between S. aureus, which is coagulase-positive, and S. epidermidis, which is coagulase-negative.

The importance of this distinction lies in the pathogenicity of S. aureus, which is known to be a significant cause of various infections, including skin infections, pneumonia, and more severe conditions such as bloodstream infections. In contrast, S. epidermidis is generally considered a skin commensal with lower pathogenicity, primarily involved in opportunistic infections, particularly in patients with indwelling medical devices.

Other test options present are less specific for this differentiation. The oxidase test is used to determine whether an organism produces cytochrome c oxidase and is typically applied to identify species in the Enterobacteriaceae family rather than staphylococci. The indole test determines the ability to convert tryptophan to indole,