Infection and Immunity, June 2000, p. 3280-3285, Vol. 68, No. 6
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Departamento de Bacteriología, Instituto Nacional de Enfermedades Infecciosas-ANLIS "Carlos G. Malbrán," 1281 Capital Federal, Argentina
Received 24 November 1999/Returned for modification 18 February 2000/Accepted 17 March 2000
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.
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