Name a common test used to identify Staphylococcus aureus.

The coagulase test is a well-established method used to identify Staphylococcus aureus, a significant pathogen often associated with a variety of infections. This test is particularly relevant because Staphylococcus aureus is the only species in the Staphylococcus genus that possesses the enzyme coagulase, which causes plasma to clot.

When performing the coagulase test, a sample from the suspected colony is mixed with plasma. If coagulase is present, the plasma will clot, confirming the identity of the organism as Staphylococcus aureus. This characteristic is crucial for distinguishing it from other staphylococci, particularly Staphylococcus epidermidis, which is coagulase-negative and does not produce this enzyme.

In contrast, the other tests mentioned serve different purposes: the lactose fermentation test is typically used for identifying lactose-fermenting bacteria like Escherichia coli, the oxidase test identifies organisms containing cytochrome oxidase and is commonly used for certain gram-negative bacteria, and the urease test detects urease production, which is characteristic of some Enterobacteriaceae and other genera but not relevant for Staphylococcus aureus identification.