This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Renal and Urinary Tract Disorders, Subject name: Gynaecology & Obstetrics
Most common causative organism of acute pyelonephritis in pregnancy is? 
Select and explain. 
A. E.coli, B. Klebsiella pneumonia, C. Enterobacter, D. Staphylococcus group
A: E.coli
Answer: A: E.coli 
Explanation: ANSWER: (A) E.coliREF: Dutta's textbook of obstetrics 6th ed page 296Incidence of pyelonephritis in pregnancy 1-3%Previous history of urinary tract infection increases chance by 50%Organisms associated are: E:coli (70%), Klebsiella (10%), Enterobacter, Proteus pseudomonas, Staphylococcus aureus