A new adhesin of Enteroaggregative Escherichia coli related to the Afa/Dr/AAF family

Statens Serum Institut, Department of Bacteriology, Mycology and Parasitology, Copenhagen, Denmark; Center for Vaccine Development, Departments of Pediatrics and Medicine, University of Maryland School of Medicine, Baltimore, MD, USA

^* To whom correspondence should be addressed. Email: jnataro{at}medicine.umaryland.edu.

	Abstract

Enteroaggregative Escherichia coli (EAEC) is an important cause of diarrhea worldwide. We analyzed 17 Danish EAEC strains, isolated in the course of a case-control study, for phenotypic and genotypic properties. The strains belonged to at least 14 different serotypes. Using PCR to investigate the prevalence of various putative virulence genes, we found that all but two strains were typical EAEC, as they harbored all or part of the previously described AggR regulon. The majority of strains harbored genes encoding Aggregative Adherence Fimbriae (AAF): most common was AAF/I, found in 9 strains; 8 strains carried no known AAF-related genes. We utilized TnphoA mutagenesis to localize the AA adhesin from one typical EAEC strain, C1010-00, which lacked a known AAF. We identified a TnphoA insertion in a hypothetical Dr-related pilin deposited in GenBank as HdaA. Four additional Danish strains harbored HdaA and all but one displayed AA to HEp-2 cells. By using PCR primers derived from the pilins and ushers from the three AAFs and Hda, we found that 16 of 17 strains exhibited evidence of one of these factors; importantly, the one negative strain also lacked the aggR gene. Cloning of the complete Hda gene cluster and expression in E. coli DH5 resulted in AA and complementation of the C1010-00 non-adherent mutant. Four related adhesins have now been found to confer AA in typical EAEC strains; our data suggest that together, these variants may account for AA in the large majority of strains.