Gram-positive cocci in clusters, catalase positive, tube coagulase positive. Which organism matches this profile?

Prepare for the CAMLPR Microbiology Test. Utilize flashcards and engaging multiple-choice questions, each equipped with descriptions and explanations. Ready yourself for an excellent performance!

Staphylococcus aureus is identified by a combination of traits: gram-positive cocci arranged in irregular clusters, catalase positivity, and the ability to convert fibrinogen to fibrin in plasma (tube coagulase positive). The cluster arrangement points to Staphylococcus species, and the catalase test confirms you’re dealing with staphylococci (they produce the enzyme catalase, unlike streptococci and enterococci). Within Staphylococcus, the tube coagulase test distinguishes the species: Staphylococcus aureus is coagulase positive, meaning it can clot plasma, while coagulase-negative staphylococci (like S. saprophyticus or S. epidermidis) do not. Bacillus species are Gram-positive rods, not cocci, so they don’t fit the profile. Since the organism is a Gram-positive coccus in clusters, catalase positive, and tube coagulase positive, the best match is Staphylococcus aureus.