What is the identification of staphylococci isolates that showed a positive tube test for free coagulase?

The identification of staphylococci isolates that show a positive tube test for free coagulase is Staphylococcus aureus. This species is uniquely characterized by its ability to produce free coagulase, an enzyme that causes the coagulation of plasma. In the laboratory, the coagulase test is employed as a crucial differentiator among staphylococci species, with Staphylococcus aureus being the only clinically relevant species that commonly gives a positive result in a tube coagulase test.

In contrast, other species such as Staphylococcus haemolyticus and Staphylococcus saprophyticus typically test negative for free coagulase. These species, while they can be found in clinical settings, do not possess the same pathogenic profile or the ability to coagulate plasma in the same way. Furthermore, Micrococcus luteus, while also part of the broader family of staphylococci, is not associated with coagulase production at all, thus confirming that it does not belong in the category with Staphylococcus aureus in this context.

Therefore, the ability to produce free coagulase is a definitive marker for diagnosing Staphylococcus aureus, affirming its role as a key pathogenic organism in various infections.