quellung reaction /kwel″ung/ [Ger, Quellung, swelling; L, re, again, agere, to act] , the swelling of the capsule of a bacterium, seen in the laboratory when the organism is exposed to specific antisera. This phenomenon is used to identify the genera, species, or subspecies of the bacteria causing a disease, including Haemophilus influenzae, Neisseria meningitidis, and many kinds of streptococci.
