Receptor specificities of variant Gal(alpha 1-4)Gal-binding PapG adhesins of uropathogenic Escherichia coli as assessed by hemagglutination phenotypes

Receptor specificities of the three recognized variants of PapG, the major adhesin of uropathogenic Escherichia coli, have been deduced in part from the distinctive hemagglutination (HA) patterns these adhesins ostensibly exhibit with different erythrocytes. A comprehensive reevaluation of these HA patterns using sheep, rabbit, and diverse human erythrocytes revealed that the erythrocyte binding ranges of the three PapG variants are broader and more overlapping than generally recognized, suggestive of receptor specificities beyond those posited in the prevailing model. Experiments involving guinea pig erythrocytes artificially labeled with defined Gal(alpha 1-4)Gal-containing glycolipids supported this hypothesis and further suggested that HA patterns with naturally occurring erythrocytes cannot be used to determine reliably an adhesin's glycolipid binding specificities. Finally, slide HA assays exhibited considerable interexperiment, interobserver, and intraobserver irreproducibility, limiting their usefulness for assessing either the receptor specificities of PapG variants or the PapG repertoire of wild-type E. coli strains.