C. trachomatis Variant Growth, Host Response
• JID 2005:192 (1 October) • 1229
M A J O R A R T I C L E
Chlamydia trachomatis Variant with Nonfusing
Inclusions: Growth Dynamic and Host-Cell
Minsheng Xia,1Robert J. Suchland,1Roger E. Bumgarner,2Tao Peng,2Daniel D. Rockey,3and Walter E. Stamm1
1Division of Infectious Diseases, Department of Medicine, and
of Biomedical Sciences, Oregon State University, Corvallis
2Center for Expression Arrays, University of Washington, Seattle;
We compared growth rate and host-cell transcriptional responses of a Chlamydia trachomatis variant strain
and a prototype strain. Growth dynamics were estimated by 16S rRNA level and by inclusion-forming units
(IFUs) at different times after infection in HeLa cells. When inoculated at the same multiplicity of infection
and observed 24–48 h after infection, the variant 16S rRNA transcriptional level was 3%–4% that of the
prototype, and the IFUs of the variant strain were 0.1%–1% those of the prototype. Specific host-cell tran-
scriptional responses to the variant were identified in a global-expression microarray in which variant strain–
infected cells were compared with mock-infected and prototype strain–infected cells. In variant strain–infected
cells, 47% (16/34) of specifically induced host genes were related to immunity and 32% (8/25) of specifically
suppressed genes were related to lipid metabolism. The variant strain grew significantly more slowly and
induced a modified host-cell transcriptional response, compared with the prototype strain.
As a sexually transmitted pathogen, Chlamydia tracho-
matis causes clinical manifestations that rangefromvir-
tually asymptomatic to clinically severe . To date,the
mechanisms by which variations in the phenotype and
genotype of the organism contribute to the diverseclin-
ical outcomes are not understood.
Chlamydiae are characterized by an obligate intra-
cellular life cycle and a unique biphasic developmental
cycle. This cycle alternates between the infectious, ex-
tracellular, metabolically inert elementary body (EB)
and the noninfectious,intracellular,metabolicallyactive
reticulate body and is accomplished within membrane-
bound vacuoles termed “inclusions” [2, 3]. We have
identified and studied a naturally occurring C. tracho-
matis variant strain that was selected from a group of
Received 2 February 2005; accepted 28 April 2005; electronically published 25
Financial support: National Institutes of Health (grants AI48769 and AI31448
and AI059404 to M.X.); University of Washington (STDCRC NewInvestigatorAward
Potential conflicts of interest: none reported.
Reprints or correspondence: Walter E. Stamm, 1959 NE Pacific St., University
of Washington, Box 356523, Seattle, WA 98195 (email@example.com).
The Journal of Infectious Diseases
? 2005 by the Infectious Diseases Society of America. All rights reserved.
isolates that exhibit unique morphological character-
istics of inclusion during development . This phe-
notype was initially discovered because multiple non-
fusing inclusions were found to coexist in a single host
cell, in contrast to infections with prototype strains, in
which only a single inclusion eventually remains dur-
ing development .Almostallstrainswiththenonfus-
ing phenotype carry mutations in the chlamydial incA
gene, which encodes the inclusion membrane protein
A (IncA), and these strains also lack IncA on the in-
nofluorescence microscopy [4, 5].
This variant phenotype accounts for ∼2% of all clin-
ical isolates recovered from patients in Seattle, and it
is associated with infections characterized by a less-se-
vere clinical course [5, 6]. Although an individual pa-
tient’s immunogenetic background certainly affects the
outcome of the infection, these data suggest that phe-
notypic variability and genotypic polymorphismsofthe
organism may also be important determinants of the
consequences of infection. Variant strains that have a
markedly altered growth rate may interact with host
cells differently and contribute to the diverse outcomes
of chlamydial infection. In the present study, we ex-
amined growth dynamics, mutations, and pathogen–
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1236 • JID 2005:192 (1 October) • Xia et al.
respond to the lymphogranuloma venereum (LGV) biovar L2
strain by a transcriptional pattern different from that induced
by the variant genital strain used in the present study . In
addition to differences in host-cell transcriptional responses,
our preliminary data indicated that the LGV strain grows even
faster than both the prototype D strain and the variant strain
in the present study (data not shown). For the present, we are
limited by available resources committed to examining only 2
isolates (the variant and the prototype); in future studies, we
will examine a diverse group of chlamydial strains for growth
and inclusion phenotypes.
We thank Dr. Kyle Serikawa, Aubree Hoover, and Mitsuhiro Tsuchiya
(Center of Expression Array, School of Medicine, University of Washing-
ton) and Dr. Edward Kelly (Center for Sequencing and Gene Analysis,
School of Pharmacy, University of Washington), for useful discussions and
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