The preferred method of differentiating Staphylococcus aureus from Staphylococcus epidermidis is?

The preferred method of differentiating Staphylococcus aureus from Staphylococcus epidermidis is the coagulase test. This test is based on the ability of Staphylococcus aureus to produce the enzyme coagulase, which causes the clotting of plasma. When a sample suspected of containing these bacteria is mixed with plasma, the presence of coagulase leads to clot formation, indicating a positive result for S. aureus.

In contrast, Staphylococcus epidermidis does not produce coagulase and thus results in no clot formation, giving a negative result. This distinctive enzymatic characteristic makes the coagulase test a reliable and straightforward method for differentiating these two species of staphylococci, as S. aureus is pathogenic and S. epidermidis is typically non-pathogenic and part of the normal skin flora.

While other tests, such as the DNase test or mannitol fermentation test, can also help in identifying S. aureus, the coagulase test is historically and clinically regarded as a more definitive method for this differentiation.