Most common cause of acute UTI:
→ 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.
E.coli
Klebsiella
Strep. faecalis
Staph. saprophyticus