Colonies isolated on Bordetella selective agar are identified preliminarily by colonial appearance, Gram stain and slide agglutination with polyvalent antiserum.
A suspension of the suspect colony should be prepared in saline on a microscope slide. Specific B. pertussis antiserum, B. parapertussis antiserum or saline should be added to the suspensions and mixed. A positive result is indicated by agglutination with one specific antiserum and no agglutination with saline.