Most common cause of acute UTI:: (A) E.coli, (B) Klebsiella, (C) Strep. faecalis, (D) Staph. saprophyticus
Answer is A. → Acute uncomplicated UTI:-  

Escherichia coli– cause about 80% of UTI. 

 
→ 20% UTI caused by:- 

Gram negative enteric bacilli – Klebsiella proteus. 
Gram positive cocci – Streptococcus faecalis. 
Staphylococcus saprophyticus - restricted to infection in young sexually active women.