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Journal of Bacteriology, October 2001, p. 5535-5543, Vol. 183, No. 19
Bacterial Pathogenesis Research Group,
Department of Microbiology, Monash University, Victoria
3800,1 and Department of Microbiology
and Infectious Diseases, Royal Children's Hospital, Parkville,
Victoria 3052,2 Australia
Received 22 March 2001/Accepted 9 July 2001
In this study, we determined the boundaries of a 99-kb deletable
element of Shigella flexneri 2a strain YSH6000. The
element, designated the multiple-antibiotic resistance deletable
element (MRDE), had recently been found to contain a 66-kb
pathogenicity island (PAI)-like element (designated the SRL PAI) which
carries the Shigella resistance locus (SRL), encoding
resistance determinants to streptomycin, ampicillin, chloramphenicol,
and tetracycline. The YSH6000 MRDE was found to be flanked by two
identical IS91 elements present at the S.
flexneri homologs of the Escherichia coli genes
putA and mdoA on NotI
fragment D. Sequence data from two YSH6000-derived MRDE deletants,
YSH6000T and S2430, revealed that deletion of the MRDE occurred between
the two flanking IS91 elements, resulting in a single
IS91 element spanning the two original
IS91 loci. Selection for the loss of tetracycline
resistance confirmed that the MRDE deletion occurred reproducibly from
the same chromosomal site and also showed that the SRL PAI and the SRL
itself were capable of independent deletion from the chromosome, thus
revealing a unique set of nested deletions. The excision frequency of
the SRL PAI was estimated to be 10
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.19.5535-5543.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Nested Deletions of the SRL Pathogenicity Island of
Shigella flexneri 2a
5 per cell in the wild
type, and mutation of a P4-like integrase gene (int) at
the left end of the SRL PAI revealed that int mediates precise deletion of the PAI.
*
Corresponding author. Mailing address: Department of
Microbiology, Monash University, Victoria 3800, Australia. Phone:
61-3-99054815. Fax: 61-3-99054811. E-mail:
Ben.Adler{at}med.monash.edu.au.
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