This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
Which one of the following gram positive organism is 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: Ans. is 'c' i.e., Staphylococcus saprophyticus(Ref: Ananthanarayan, 9th/e, p. 206 and 8th/e, p. 202)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.Note: Most common cause is E. coli, which is not provided in the option.