Infect Immun, July 1998, p. 3155-3163, Vol. 66, No. 7
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Department of Public Health, Faculty of Medicine, UNAM, 04510 Mexico DF, Mexico,1 and Center for Vaccine Development, Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland 212012
Received 9 February 1998/Returned for modification 25 March 1998/Accepted 20 April 1998
Enteroaggregative Escherichia coli (EAEC) is an
emerging cause of diarrheal illness. Clinical data suggest that
diarrhea caused by EAEC is predominantly secretory in nature, but the
responsible enterotoxin has not been described. Work from our
laboratories has implicated a ca. 108-kDa protein as a heat-labile
enterotoxin and cytotoxin, as evidenced by rises in short-circuit
current and falls in tissue resistance in rat jejunal tissue mounted in an Ussing chamber. Here we report the genetic cloning, sequencing, and
characterization of this high-molecular-weight heat-labile toxin. The
toxin (designated the plasmid-encoded toxin [Pet]) is encoded on the
65-MDa adherence-related plasmid of EAEC strain 042. Nucleotide
sequence analysis suggests that the toxin is a member of the
autotransporter class of proteins, characterized by the presence of a
conserved C-terminal domain which forms a
-barrel pore in the
bacterial outer membrane and through which the mature protein is
transported. The Pet toxin is highly homologous to the EspP protease of
enterohemorrhagic E. coli and to EspC of enteropathogenic
E. coli, an as yet cryptic protein. In addition to its
potential role in EAEC infection, Pet represents the first enterotoxin
within the autotransporter class of secreted proteins. We hypothesize
that other closely related members of this class may also produce
enterotoxic effects.
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