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Infection and Immunity, January 2000, p. 360-367, Vol. 68, No. 1
Division of Allergy and Infectious Diseases,
School of Medicine, University of Washington, Seattle,
Washington,1 and Department of
Microbiology, Oregon State University, Corvallis,
Oregon2
Received 13 July 1999/Returned for modification 20 August
1999/Accepted 4 October 1999
The chlamydiae are obligate intracellular pathogens that occupy a
nonacidified vacuole, termed an inclusion, throughout their developmenal cycle. When an epithelial cell is infected with multiple Chlamydia trachomatis elementary bodies, they are
internalized by endocytosis into individual phagosomal vacuoles that
eventually fuse to form a single inclusion. In the course of
large-scale serotyping studies in which fluorescent antibody staining
of infected cells was used, a minority of strains that had an alternate
inclusion morphology were identified. These variants formed multiple
nonfusogenic inclusions in infected cells, with the number of
independent inclusions per cell varying directly with the multiplicity
of infection. Overall the nonfusogenic phenotype was found in 1.5%
(176 of 11,440) of independent isolates. Nonfusing variants were seen
in C. trachomatis serovars B, D, D
0019-9567/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Isolates of Chlamydia trachomatis That
Occupy Nonfusogenic Inclusions Lack IncA, a Protein Localized to the
Inclusion Membrane
, E, F, G, H, Ia, J,
and K. The nonfusing phenotype persisted through repeated serial
passage, and the phenotype was consistent in four mammalian host cell
lines. Fluorescence microscopy and immunoblotting with antisera
directed at proteins in the C. trachomatis inclusion
membrane revealed that one such protein, IncA, was not detected in the
inclusion membrane in each tested nonfusogenic strain. The
distributions of other chlamydial proteins, including one additional
Inc protein, were similar in wild-type and variant strains. The
incA coding and upstream regions were amplified and
sequenced from the prototype serovar D and two nonfusing serovar
D(s) strains. Three nucleotide changes were discovered in
the D(s) incA gene, leading to two amino acid
changes within the predicted D(s) IncA sequence. These
studies demonstrate a subgroup of variant C. trachomatis
isolates that form nonfusing inclusions; the variant phenotype is
associated with the absence of detectable IncA and with an altered
incA sequence that modifies the characteristic hydrophobic
domain of the IncA protein.
*
Corresponding author. Mailing address: Chlamydia
Laboratory, Harborview Medical Center, Box 359742, 325 Ninth Ave.,
Seattle, WA 98104-2499. Phone: (206) 341-5300. Fax: (206)
341-5304. E-mail: badbob{at}u.washington.edu.
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