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Infect. Immun., 07 1996, 2585-2594, Vol 64, No. 7
MS Swanson and RR Isberg
After uptake by macrophages, Legionella pneumiophila evades phagosome-
lysosome fusion and replicates in a compartment associated with the
endoplasmic reticulum. A collection of bacterial mutants defective for
growth in macrophages were isolated, and the intracellular fate of each
mutant strain was analyzed by fluorescence microscopy. To measure
intracellular replication, bacteria inside macrophages were stained with
the DNA dye 4',6-diamidino-2-phenylindole (DAPI). Evasion of the endocytic
pathway was quantified by immunofluorescence localization of lp120
[correction of IgpI20] (LAMP-1), a membrane protein of late endosomes and
lysosomes, or by measuring colocalization of bacteria with a fluorescent
tracer, Texas red-ovalbumin, preloaded into lysosomes. Replication vacuoles
were quantified by immunofluorescence localization of BiP, an endoplasmic
reticulum protein. By these approaches, four phenotypic groups of mutants
were classified. One class formed replication vacuoles less efficiently
than the wild type did; another formed replication vacuoles, but
replication was abortive; in another class, most phagosomes containing
bacteria acquired markers of the endocytic pathway but a minority formed
replication vacuoles and the bacteria replicated; finally, a fourth class,
the one most defective for intracellular growth, occupied vacuoles that
acquired markers of the endocytic pathway.
Copyright © 1996, American Society for Microbiology
Identification of Legionella pneumophila mutants that have aberrant intracellular fates
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
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