A 47 year old man with a history of sickle cell disease has had numerous hospitalizations requiring the placement of intravenous lines. The patient has poor peripheral venous access, and a catheter is placed in the right subclan vein. The patient subsequently develops right arm discomfo and swelling and a temperature of 40.1 degrees C with chills. Multiple blood cultures are taken, and gram-positive cocci are isolated. The organism is catalase positive and grows on mannitol salt agar, but does not turn the agar yellow; the colonies are gamma-hemolytic on a sheep blood agar plate. Which of the following organisms is the most likely cause of this patient’s symptoms?

**Core Concept**
The patient's symptoms and laboratory findings suggest a case of bacteremia caused by a gram-positive coccus that is catalase positive, grows on mannitol salt agar, but does not produce acid from mannitol, and is gamma-hemolytic on sheep blood agar. This organism is likely to be a common cause of skin and soft tissue infections.

**Why the Correct Answer is Right**
The organism in question is likely Staphylococcus saprophyticus, a catalase-positive, gram-positive coccus that grows on mannitol salt agar but does not ferment mannitol. This is in contrast to Staphylococcus aureus, which ferments mannitol and produces a yellow color on mannitol salt agar. S. saprophyticus is a common cause of urinary tract infections and bacteremia, particularly in patients with indwelling catheters. The patient's symptoms, including fever, chills, and arm discomfort, are consistent with a diagnosis of bacteremia.

**Why Each Wrong Option is Incorrect**
* **Option A:** Staphylococcus aureus is catalase-positive, gram-positive coccus that grows on mannitol salt agar and ferments mannitol, producing a yellow color. This is in contrast to the organism described in the case.
* **Option B:** Staphylococcus epidermidis is also a catalase-positive, gram-positive coccus that grows on mannitol salt agar, but it is typically coagulase-negative and does not cause the same level of morbidity as the organism described in the case.
* **Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
S. saprophyticus is a common cause of urinary tract infections in young, sexually active women, but it can also cause bacteremia in patients with indwelling catheters. The organism's ability to grow on mannitol salt agar but not ferment mannitol can be used to differentiate it from S. aureus.

**Correct Answer:** B.

✓ Correct Answer: C. Staphylococcus epidermidis