Serologic Methods: Counterimmunoelectrophoresis (CIE)

1. Modification of the Ouchterlony method.
2. Unknown bacterial antigen and a known specific antibody move towards each other in an electrical field
3. Most bacterial antigen are negatively charged  (eg. Capsular polysaccharide) in a slightly alkaline environment.
4. When Ag and Ab meet in optimal proportions, a line of precipitation appear within the agar matrix 
5. The entire procedure takes about One hour. 
6. Any antigen for which antisera is available can be tested by CIE Sensivity less than that of particle agglutination (0.01-0.05 mg/ml) of antigen.

Used to detect presence of capsular antigens in CSF of

• H. influenzae
• N. meningitidis
• S. Pneumoniae etc

 CIE is  more expensive than agglutination based tests.
Initial capital outlay for the apparatus
Nee of large quantity of Ag and Ab