This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
In a patient of the nephritic syndrome with spontaneous bacterial peritonitis, which one of the following micro-organisms is most commonly involved? 
Select and explain. 
A. Proteus, B. Escherichia, C. Pneumococcus, D. Staphylococcus
B: Escherichia
Answer: B: Escherichia 
Explanation: Spontaneous bacterial peritonitis means peritonitis without any apparent source of contamination.Enteric gram-negative organism E. coli most commonly encountered but sometime gram-positive organisms such as streptococci and enterococci also responsible.