Differentiation between staphylococcus aureus and epidermidis is done by?

ANSWER: (C) CoagulaseREF: Jawetz Microbiology, 24th Ed Ch 14The genus Staphylococcus has at least 35 species. The three main species of clinical importance are Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus saprophyticus.* Staphylococcus aureus is coagulase-positive, which differentiates it from the other species. The coagulase-negative staphylococci are normal human flora and sometimes cause infection, often associated with implanted appliances and devices, especially in very young, old, and immunocompromised patients.* Approximately 75% of these infections caused by coagulase-negative staphylococci are due to S epidermidis. Staphylococci produce catalase, which converts hydrogen peroxide into water and oxygen. The catalase test differentiates the staphylococci, which are positive, from the streptococci, which are negative.S saprophyticus is typically nonpigmented, novobiocin-resistant, and nonhemolytic; it causes urinary tract infections in young women. Resistance to nafcillin (and oxacillin and methicillin) occurs in about 35% of S aureus and approximately 75% of S epidermidis isolates. So it cannot be used to differentiate them.