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J Bacteriol, June 1998, p. 2983-2986, Vol. 180, No. 11
Department of Microbiology, The University of
Sydney, Sydney, New South Wales 2006, Australia
Received 6 November 1997/Accepted 20 March 1998
O antigen is part of the lipopolysaccharide present in the outer
membrane of gram-negative bacteria. The surface-exposed O antigen is
subject to selection by the host immune system, which may account for
the maintenance of many different O-antigen forms. Characteristically,
all genes specific to O-antigen synthesis are clustered in a region
close to the his and gnd genes on the chromosome of Escherichia coli and related species.
Shigella sonnei, essentially a clone of E. coli
(E. coli clone Sonnei), is an important human pathogen and
is unusual in that its O-antigen gene cluster is located on a plasmid.
Our results suggest that it once had a normal chromosomal O-antigen
gene cluster which has been largely deleted. We suggest that the O
antigen encoded by the plasmid-borne genes offered a selective
advantage in adapting to a new environment and that the chromosomal
O-antigen genes were eventually inactivated. We also identified, by PCR
and sequencing, a potential ancestor of E. coli Sonnei
among the 166 known E. coli serotype strains.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Escherichia coli Clone Sonnei (Shigella
sonnei) Had a Chromosomal O-Antigen Gene Cluster Prior to Gaining
Its Current Plasmid-Borne O-Antigen Genes
*
Corresponding author. Mailing address: Department of
Microbiology, The University of Sydney, Sydney, N.S.W. 2006, Australia. Phone: (612) 351 2536. Fax: (612) 351 4571. E-mail:
reeves{at}angis.su.oz.au.
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