This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Streptococci, Subject name: Microbiology
A chronic alcoholic is presenting with clinical features of meningitis. Most likely organism which will grow on CSF culture - 
Select and explain. 
A. Streptococcus pneumoniae, B. N. meningitidis, C. Listeria monocytogenes, D. E coli
A: Streptococcus pneumoniae
Answer: A: Streptococcus pneumoniae 
Explanation: Ans. is 'a' i.e., Streptococcus pneumoniae o Streptococcus pneumoniae is the most common cause of meningitis in adults older than 20 years of age.o A number of predisposing conditions increase the risk of pneumococcal meningitis, the most common of which is pneumonia.o Additional risk factors include alcoholism, acute and chronic otitis media, diabetes, splenectomy, hypogamaglobulinemia and head trauma with basilar skull fracture and CSF leak.