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

Abstract

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.

ECA, the enterobacterial common antigen

“…But the variation of individual strains within a species can, in many cases, be as high as differences between species or genera and may also depend on the growth phase. Using monoclonal ECA antibodies and the EIA system, this large variation in ECA content was confirmed recently [7]. The variation in the amount of ECA precludes the use of ECA as genus-or speciesspecific quantitative marker.…”

“…Recently, using monoclonal ECA antibodies for detection, the presence of tiny amounts of ECA in heated supernatants of Actinobacillus equuli and Actinobacillus suis (but not in other Actinobacilli) was reported [7]. However, chemical analyses demonstrated the lack of typical ECA components in both species [9].…”

“…The value of ECA as an additional criterium for taxonomical problems may be illustrated by the occurrence of ECA in Yersinia and its absence in Pasteurella multocida and Pasteurella haernolytica: this is in excellent agreement with the elimination of Yersinia from the genus Pasteurella and its addition to the Enterobacteriaceae as a new genus. In two recent studies [7,8], newly classifted species of the Enterobacteriaceae and Vibrionaceae were screened for ECA. All species classified as Enterobacteriaceae contain ECA, whereas all the others lack it (Table 1); this confirms the value of ECA for taxonomic classification.…”

“…The localization of ECA in the outer membrane (see section 7) raised the question about the anchoring of this hydrophilic sugar chain in the membrane; that means, on a lipid moiety. Indeed, small amounts of fatty acids were found in ECA of Salmonella and Shigella [15,16].…”

“…ECA is present in all enterobacterial wild-type strains and, unlike hpopolysaecharides and capsular antigens, has an identical structure in all species tested so far; Table 1 Distribution of ECA in wild-type strains of Gram-negative bacteria [4,7,8] * see text (p. 197 ECA is restricted to the Enterobacteriaceae whereas other bacterial antigens (e.g., lipopolysaccharide, major outer membrane proteins, lipoprotein) also occur in other Gram-negative families;…”