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Qualitative and quantitative determination of enterobacterial common antigen (ECA) with monoclonal antibodies: expression of ECA by two Actinobacillus species

The presence and quantity of the enterobacterial common antigen (ECA) in several species belonging to the family Enterobacteriaceae as well as to other gram-negative families were determined by a solid-phase enzyme-linked immunosorbent assay system and Western blotting by using mouse monoclonal antibodies specific for ECA. Except for Erwinia chrysanthemi, previously known to be an exception, all species known or presumed to belong to Enterobacteriaceae produced ECA (89 of 90 species). Most species not belonging to Enterobacteriaceae did not produce ECA (25 of 28 species), with one already known (Plesiomonas shigelloides) and two hitherto unknown (Actinobacillus equuli and Actinobacillus suis) exceptions. Interestingly, all strains of P. shigelloides produced ECA, regardless of the presence of the Shigella sonnei cross-reacting O antigen. Quantitation of the amount of ECA in members of the family Enterobacteriaceae revealed a remarkable heterogeneity among genera and species as well as within one species. We conclude that the rapid, sensitive, and reliable determination of ECA is a useful aid in taxonomic classification and may help to characterize the relatedness of the family Enterobacteriaceae to other families. However, a quantitative analysis of ECA appears to be without value for these purposes.