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Infection and Immunity, March 2001, p. 1344-1350, Vol. 69, No. 3
Department of Medicine, Oklahoma University
Health Sciences Center and the Harold Muchmore Laboratories for
Infectious Diseases Research of the Veterans Administration Medical
Center, Oklahoma City, Oklahoma,1 and
The Seattle Biomedical Research Institute, Seattle,
Washington2
Received 8 August 2000/Returned for modification 15 September
2000/Accepted 17 November 2000
Listeria monocytogenes-infected phagocytes are present
in the bloodstream of experimentally infected mice, but whether they play a role in central nervous system (CNS) invasion is unclear. To
test whether bacteria within infected leukocytes could
establish CNS infection, experimentally infected mice were treated with gentamicin delivered by surgically implanted osmotic pumps. Bacterial inhibitory titers in serum and plasma ranged from 1:16 to 1:256, and
essentially all viable bacteria in the bloodstream of treated mice were
leukocyte associated. Nevertheless, CNS infection developed in
gentamicin-treated animals infected intraperitoneally or by gastric
lavage, suggesting that intracellular bacteria could be responsible for
neuroinvasion. This was supported by data showing that 43.5% of
bacteria found with blood leukocytes were intracellular and some
colocalized with F-actin, indicating productive intracellular parasitism. Experiments using an L. monocytogenes strain
containing a chromosomal actA-gfpuv-plcB transcriptional
fusion showed that blood leukocytes were associated with intracellular
and extracellularly bound green fluorescent protein-expressing
(GFP+) bacteria. Treatment with gentamicin decreased the
numbers of extracellularly bound GFP+ bacteria
significantly but did not affect the numbers of intracellular GFP+ bacteria, suggesting that the latter were the result
of intercellular spread of GFP+ bacteria to leukocytes.
These data demonstrate that infected leukocytes and the intracellular
L. monocytogenes harbored within them play key roles in
neuroinvasion. Moreover, they suggest that phagocytes recruited to
infected organs such as the liver or spleen are themselves parasitized
by intercellular spread of L. monocytogenes and then
reenter the bloodstream and contribute to the systemic dissemination of bacteria.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.3.1344-1350.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Listeria monocytogenes-Infected
Phagocytes Can Initiate Central Nervous System Infection in
Mice
*
Corresponding author. Mailing address: Section of
Infectious Diseases, University of Oklahoma Health Sciences Center, VA
Medical Center (111/c), Oklahoma City, OK 73104. Phone: (405) 270-0501, ext. 3284. Fax: (405) 297-5934. E-mail:
douglas-drevets{at}ouhsc.edu.
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