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Infection and Immunity, July 2001, p. 4398-4406, Vol. 69, No. 7
Department of Molecular Genetics and
Microbiology, University of Florida, Gainesville, Florida 32610
Received 12 October 2000/Returned for modification 25 January
2001/Accepted 21 March 2001
Clinical isolates of Pseudomonas aeruginosa are
classified into invasive and noninvasive (cytolytic) strains. In a
noninvasive PA103 background, ExoS and ExoT have recently been shown to
function as anti-internalization factors. However, these two factors
seemed not to have such a function in an invasive strain PAK
background. In this study, using HeLa tissue culture cells, we observed
that the internalization of invasive strain PAK is dependent on its growth phases, with the stationary-phase cells internalized about 100-fold more efficiently than the exponential-phase cells. This growth
phase-dependent internalization was not observed in the noninvasive
PA103 strain. Further analysis of various mutant derivatives of the
invasive PAK and the noninvasive PA103 strains demonstrated that ExoS
or ExoT that is injected into host cells by a type III secretion
machinery functions as an anti-internalization factor in both types of
strains. In correlation with the growth phase-dependent internalization, the invasive strain PAK translocates much higher amount of ExoS and ExoT into HeLa cells when it is in an
exponential-growth phase than when it is in a stationary-growth phase,
whereas the translocation of ExoT by the noninvasive strain PA103 is
consistently high regardless of the growth phases, suggesting a
difference in the regulatory mechanism of type III secretion between
the two types of strains. Consistent with the invasive phenotype of the
parent strain, an internalized PAK derivative survived well within the
HeLa cells, whereas the viability of internalized PA103 derivative was
dramatically decreased and completely cleared within 48 h. These
results indicate that the invasive strains of P. aeruginosa have evolved the mechanism of intracellular survival, whereas the
noninvasive P. aeruginosa strains have lost or not acquired the ability to survive within the epithelial cells.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.7.4398-4406.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Growth Phase-Dependent Invasion of
Pseudomonas aeruginosa and Its Survival within HeLa
Cells
*
Corresponding author. Mailing address: Department of
Molecular Genetics and Microbiology, P.O. Box 100266, University of
Florida, Gainesville, FL 32610-0266. Phone: (352) 392-8323. Fax: (352) 392-3133. E-mail: sjin{at}mgm.ufl.edu.
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