Laboratory Diagnosis of Enteropathogenic Escherichia coli in Calves

Tests were carried out on 33 E. coli isolates previously designated as enteropathogenic. Each isolate was critically retested using the slide agglutination procedure with both the polyvalent bovine OK antiserum as well as specific K99 antiserum, using the infant mouse inoculation test, and using ligated intestinal loops in newborn calves. Only four of the 33 E. coli isolates were subsequently confirmed as being enteropathogenic, showing that a major laboratory error in the diagnosis of E. coli isolates as "enteropathogenic" had been made. These results are submitted to emphasize that the rapid slide agglutination test with polyvalent bovine OK antiserum must be interpreted accurately at the time of mixing. Delay in viewing the slide or the misinterpretation of nonspecific clumping for agglutination can lead to false positive results. It is essential that laboratory personnel be aware of this problem with the rapid slide agglutination test and periodically monitor their work.