This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Quellung reaction is seen in ? 
Select and explain. 
A. Group B streptococcus, B. Staphylococcus, C. Pneumococcus, D. Enterococcus
C: Pneumococcus
Answer: C: Pneumococcus 
Explanation: Ans. is 'c' i.e., Pneumococcus A suspension of pneumococci is mixed on a slide with a drop of the type specific antiserum and methylene blue. On the presence of homologous antiserum capsule becomes apparently swollen, sharply delineated and refractile. This is called Quellung reaction.