CS22, a Novel Human Enterotoxigenic Escherichia coli Adhesin, Is Related to CS15

Abstract

Enterotoxigenic Escherichia coli (ETEC) expresses a broad spectrum of O:H antigens. Serogroup O20 is one of the most prevalent among the ETEC strains lacking any of the defined colonization factors (CFs), in Argentina. An O20:H؊ strain, ARG-3, adhered to Caco-2 cells and exhibited a thermoregulated 15.7-kDa protein band upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). An antiserum against this protein inhibited ARG-3 adhesion to Caco-2 cells and bound to very thin fibrilla-like structures on the bacterial surface. A 15.7-kDa protein-defective mutant failed to adhere to Caco-2 cells and lacked immunogold-labeled surface structures. The N-terminal amino acid sequence of the structural subunit showed 95% homology to that of CS15 of ETEC (former antigen 8786) and 65% homology with fimbria SEF14 of Salmonella enterica serovar Enteritidis. Nevertheless, the molecular size of ARG-3 adhesin was different from that of CS15, as revealed by SDS-PAGE and mass spectrometry. Both proteins are immunologically related, yet not identical, since an antiserum against the 15.7-kDa protein reacted solely with ARG-3 after absorption with bacteria bearing CS15. Moreover, only under low stringency conditions could DNA from strain ARG-3 be amplified by PCR using primers derived from the nfaA sequence of CS15. Thus, from the DNA sequence obtained from the ARG-3 PCR product, it could be deduced that the subunit protein differed in 30 residues from that of CS15. ARG-3 adhesin was found in 60% of the O20:H-CF-negative ETEC strains from Argentina; however, it appeared restricted to this serotype. We propose the designation CS22 for the herein identified nonfimbrial adhesin of human ETEC.

Phenotypic and Genotypic Analysis of Enterotoxigenic Escherichia coli in Samples Obtained from Egyptian Children Presenting to Referral Hospitals

“…coli pathovars are diverse microorganisms composed of several clones, the genetic background of each of which encodes distinct combinations of virulence determinants. Accordingly, use of the conventional classification of E. coli by Oand H-antigen serotyping may restrict our appreciation of the genetic relationship of different diarrheagenic E. coli pathotypes (7,24,26,27). Phenotypic and genotypic heterogeneity has been demonstrated among ETEC isolates of similar serogroups, such as O153 and O20 (21,43).…”

“…To date, more than 20 ETEC CFs have been characterized (11,27). The diversity of ETEC CFs is due to differences in the primary amino acid sequences of the adhesive fimbrial structural subunits.…”

Type IV Longus Pilus of Enterotoxigenic Escherichia coli : Occurrence and Association with Toxin Types and Colonization Factors among Strains Isolated in Argentina

“…ETEC adheres to enterocytes by means of appendages termed colonization factors (CFs), which include the colonization factor antigens (CFAs) and putative colonization factors (PCFs). So far, 21 different CFs have been described; they can be grouped into families according to amino acid sequence similarities of their structural subunits (6,24). In addition, a large proportion of ETEC strains produce a type IV pilus called longus (9).…”

Identification of a Cluster of Strains Bearing a New Adhesin among Genetically Diverse Enterotoxigenic Escherichia coli Isolates of Serogroup O20

“…By means of a combination of DNA typing approaches and adhesion to Caco-2 cells, we could identify a genetically related, yet not identical, group of strains that bear the recently described adhesin CS22 (10).…”