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Infection and Immunity, October 1998, p. 4700-4710, Vol. 66, No. 10
Department of Microbiology and Institute for
Cellular and Molecular Biology, University of Texas at Austin,
Austin, Texas 78712
Received 25 March 1998/Returned for modification 26 May
1998/Accepted 21 July 1998
The ability of Shigella flexneri to multiply within
colonic epithelial cells and spread to adjacent cells is essential for production of dysentery. Two S. flexneri chromosomal loci
that are required for these processes were identified by screening a
pool of TnphoA insertion mutants. These mutants were able
to invade cultured epithelial cells but could not form wild-type plaques. Analysis of the nucleotide sequence indicated that the sites
of TnphoA insertion were within two different regions that are almost identical to Escherichia coli K-12 chromosomal
sequences of unknown functions. One region is located at 70 min on the
E. coli chromosome, upstream of murZ, while the
other is at 28 min, downstream of tonB. The mutant with the
insertion at 70 min was named vpsC because it showed an
altered pattern of virulence protein secretion. The vpsC
mutant formed pinpoint-sized plaques, was defective in recovery from
infected tissue culture cells, and was sensitive to lysis by the
detergent sodium dodecyl sulfate. Recombinant plasmids carrying the
S. flexneri vpsA, -B, and -C genes
complemented all of the phenotypes of the vpsC mutant. A mutation in vpsA resulted in the same phenotype as the
vpsC mutation, suggesting that these two genes are part of
a virulence operon in S. flexneri. The mutant with the
insertion at 28 min was interrupted in the same open reading frame as
S. flexneri ispA. This ispA mutant could not
form plaques and was defective in bacterial septation inside tissue
culture cells.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Identification of Two Shigella flexneri
Chromosomal Loci Involved in Intercellular Spreading

*
Corresponding author. Mailing address: Department of
Microbiology, University of Texas at Austin, Austin, TX 78712-1095. Phone: (512) 471-9258. Fax: (512) 471-7088. E-mail:
payne{at}mail.utexas.edu.
Present address: Department of Structural Biology, Stanford
University School of Medicine, Stanford, CA 94305-5400.
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