This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Which one of the following gram-positive organism is the most common cause of UTI among sexually active women- 
Select and explain. 
A. Staphylococcus epidermidis, B. Staphylococcus aureus, C. Staphylococcus saprophyticus, D. Enterococcus
C: Staphylococcus saprophyticus
Answer: C: Staphylococcus saprophyticus 
Explanation: Staph saprophyticus 

Staph saprophyticus may be present on normal human skin and the periurethral area and can cause urinary tract infection, particularly in sexually active young women.
Staph saprophyticus strains causing UTI are usually sensitive to most antibiotics, except nalidixic acid.
Staph saprophyticus is novobiocin resistant.