Which of the following bacteria is coagulase positive?

The identification of coagulase-positive bacteria is significant in microbiology, particularly in differentiating between various species of Staphylococcus. Staphylococcus aureus is the only species among the choices provided that is coagulase positive. Coagulase is an enzyme that allows the bacterium to clot blood plasma, which is a trait that can help in diagnosing infections caused by S. aureus, as this species can cause a variety of diseases ranging from skin infections to more severe bloodstream infections.

The ability to produce coagulase also has clinical implications, as S. aureus is often associated with more pathogenic strains compared to its coagulase-negative counterparts. Infections caused by coagulase-positive bacteria like Staphylococcus aureus can be more serious and are known to produce toxins, which play a role in the disease progression and symptoms observed in patients.

In contrast, the other listed organisms, Staphylococcus epidermidis and the Streptococcus species (agalactiae and pyogenes), are all coagulase negative. This distinction is critical in clinical diagnostics and treatment decisions, underscoring the importance of identifying coagulase positive bacteria accurately.