Comparison of counterimmunoelectrophoresis and the capsular reaction test for typing of pneumococci.

The capsular reaction test is recommended as the method of choice for typing of pneumococci. Counterimmunoelectrophoresis also works in most cases, but has the following definite drawbacks. (i) The polysaccharide type antigens of types 7F, 7A, 14, 33F, 33A, and 37 are neutral and therefore do not form precipitates when conventional buffers are used. (ii) Counterimmunoelectrophoresis does not permit differentiation between types within groups since many factor sera do not contain sufficient amounts of precipitating antibodies. Omniserum contains low-titered antibodies against cell wall antigens and also reacts with thioglycolate-containing broth.