Comparison of the Direct Agglutination and Indirect Hemagglutination Tests in the Determination of Blood Serum Titers to Escherichia coli Organisms

A comparison of the direct agglutination test and the indirect hemagglutination test for the detection of blood serum antibodies to Escherichia coli organisms indicated that these serological tests were comparable. In some instances the indirect hemagglutination test provided higher endpoint readings. Preparation of the antigens for the indirect hemagglutination test was more time consuming than for the direct agglutination test. Crude extract and purified polysaccharides were comparable as red blood cell sensitizing agents.