Quellung reaction is seen in ?
Group B streptococcus
Staphylococcus
Pneumococcus
Enterococcus
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.