Evaluation of a simplified procedure for serotyping Campylobacter jejuni and Campylobacter coli which is based on the O antigen.

A simplified procedure for serotyping Campylobacter jejuni and Campylobacter coli on the basis of thermostable antigens was developed and tested for its applicability as a routine typing method. The assay involves the sensitization of erythrocytes with an antigenic extract and performance of a slide agglutination assay with specific antisera. In order to simplify the typing system to a greater extent, the standard typing antisera were pooled into nine groups for C. jejuni and four groups for C. coli. The five antiserum samples allocated to each pool were selected so that pairs or groups of cross-reacting antisera were included in the same pool. When this system was tested with the serotype reference strains, it was found that, in most cases, a strain reacted in only one pool. The specific serotype of that strain could then be further defined by typing in each of the antisera belonging to that pool. To evaluate the specificity of the simplified method, 246 clinical isolates of C. jejuni and 57 clinical isolates of C. coli were typed at the same time by the standard passive hemagglutination assay and by the rapid slide agglutination system. Although both schemes effectively differentiated isolates and results from both schemes were generally very similar, differences were noted for a few isolates. On the basis of these findings, the simplified procedure may be recommended as an alternative means for serotyping these species for epidemiological purposes.