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Infect Immun, June 1998, p. 2471-2485, Vol. 66, No. 6
Department of Molecular Genetics and
Microbiology,
Received 13 October 1997/Returned for modification 6 January
1998/Accepted 7 March 1998
The 90-kb virulence plasmid of Salmonella typhimurium
encodes five spv genes which increase the growth rate of
the bacteria within host cells within the first week of systemic
infection of mice (P. A. Gulig and T. J. Doyle, Infect.
Immun. 61:504-511, 1993). The presently described study was aimed at
identifying the host cells associated with Spv-mediated virulence
by manipulating the mouse host and the salmonellae. To test the effects
of T cells and B cells on the Spv phenotype, salmonellae were orally
inoculated into nude and SCID BALB/c mice. Relative to normal BALB/c
mice, nude and SCID BALB/c mice were unaffected for splenic infection with either the Spv+ or Spv
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Analysis of Host Cells Associated with the Spv-Mediated Increased
Intracellular Growth Rate of Salmonella typhimurium in
Mice
S. typhimurium strains at 5 days postinoculation. When mice were pretreated with cyclophosphamide to induce granulocytopenia, there was a variable increase in total salmonella infection, but the relative
splenic CFU of Spv+ versus Spv
S. typhimurium was not changed after oral inoculation. In contrast, depletion of macrophages from mice by treatment with cyclophosphamide plus liposomes containing dichloromethylene diphosphate resulted in
equivalent virulence of Spv+ and Spv
salmonellae. To examine if the spv genes affected the
growth of salmonellae in nonphagocytic cells, an
invA::aphT mutation was transduced
into Spv+ and Spv
S. typhimurium
strains. InvA
Spv+ salmonellae were not
significantly affected for splenic infection after subcutaneous
inoculation compared with the wild-type strain, and InvA
Spv
salmonellae were only slightly attenuated relative to
InvA+ Spv
salmonellae. Invasion-defective
salmonellae still exhibited the Spv phenotype. Therefore, infection of
nonphagocytes is not involved with the Spv virulence function. Taken
together, these data demonstrate that macrophages are essential for
suppressing the infection by Spv
S. typhimurium, by serving as the primary host cell for
Spv-mediated intracellular replication and possibly by inhibiting the
replication of salmonellae within other macrophages.
*
Corresponding author. Mailing address: Department of
Molecular Genetics and Microbiology, University of Florida College of Medicine, Gainesville, FL 32610-0266. Phone: (352) 392-0050. Fax: (352)
392-3133. E-mail: gulig{at}college.med.ufl.edu.
Infect Immun, June 1998, p. 2471-2485, Vol. 66, No. 6
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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