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Chlamydia psittaci genetic variants differ in virulence by modulation of host immunity.

ABSTRACT: Psittacosis is a zoonosis caused by Chlamydia psittaci and is characterized by severe pneumonia and systemic infection. We sought to determine the basis of the 1000-fold difference in lethal dose of 2 C. psittaci 6BC strains in mice.Genomes of the strains were sequenced. Mice were infected intraperitoneally and the growth kinetics, immune responses, and pathology were compared.The 2 strains differed by the presence of a 7.5-kb plasmid in the attenuated strain and 7 nonsynonomous single-nucleotide polymorphisms between the chromosomes, including a serine/threonine protein kinase gene pkn5. The plasmid was cured from the attenuated strain, but it remained nonlethal. Strains did not differ in growth kinetics in vitro or in vivo. Infection with the attenuated strain led to influx of activated macrophages with relatively minor organ damage. In contrast, the virulent strain caused an influx of nonactivated macrophages, neutrophils, and significant end organ damage. Mice infected with the virulent strain survived challenge when coinfected with either the plasmid-positive or plasmid-negative attenuated strain, indicating that an active process elicited by the attenuated strain reduces inflammation and disease.C. psittaci modulates virulence by alteration of host immunity, which is conferred by small differences in the chromosome.

SUBMITTER: Miyairi I

PROVIDER: S-EPMC3203387 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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Chlamydia psittaci genetic variants differ in virulence by modulation of host immunity.

Miyairi Isao I Laxton Jonathan D JD Wang Xiaofei X Obert Caroline A CA Arva Tatireddigari Venkat R R VR van Rooijen Nico N Hatch Thomas P TP Byrne Gerald I GI

The Journal of infectious diseases 20110801 4

<h4>Background</h4>Psittacosis is a zoonosis caused by Chlamydia psittaci and is characterized by severe pneumonia and systemic infection. We sought to determine the basis of the 1000-fold difference in lethal dose of 2 C. psittaci 6BC strains in mice.<h4>Methods</h4>Genomes of the strains were sequenced. Mice were infected intraperitoneally and the growth kinetics, immune responses, and pathology were compared.<h4>Results</h4>The 2 strains differed by the presence of a 7.5-kb plasmid in the att ...[more]

PMID: 21791668

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Project description:The obligate intracellular bacterium Chlamydia psittaci is a known avian pathogen causing psittacosis in birds and is capable of zoonotic transmission. In human pulmonary infections, C. psittaci can cause pneumonia associated with significant mortality if inadequately diagnosed and treated. Although intracellular C. psittaci manipulates host cell organelles for its replication and survival, it has been difficult to demonstrate host-pathogen interactions in C. psittaci infection due to the lack of easy-to-handle genetic manipulation tools. Here, we show the genetic transformation of C. psittaci using a plasmid shuttle vector that contains a controllable gene induction system. The 7,553-bp plasmid p01DC12 was prepared from the nonavian C. psittaci strain 01DC12. We constructed the shuttle vector pCps-Tet-mCherry using the full sequence of p01DC12 and the 4,449-bp fragment of Chlamydia trachomatis shuttle vector pBOMB4-Tet-mCherry. pCps-Tet-mCherry includes genes encoding the green fluorescent protein (GFP), mCherry, and ampicillin resistance (AmpR). Target genes can be inserted at a multiple cloning site (MCS). Importantly, these genes can be regulated by a tetracycline-inducible (tet) promoter. Using the pCps-Tet-mCherry plasmid shuttle vector, we show the expression of GFP, as well as the induction of mCherry expression, in C. psittaci strain 02DC15, which belongs to the avian C. psittaci 6BC clade. Furthermore, we demonstrated that pCps-Tet-mCherry was stably retained in C. psittaci transformants. Thus, our C. psittaci plasmid shuttle vector system represents a novel targeted approach that enables the elucidation of host-pathogen interactions.IMPORTANCE Psittacosis, caused by avian C. psittaci, has a major economic impact in the poultry industry worldwide and represents a significant risk for zoonotic transmission to humans. In the past decade, the tools of genetic manipulation have been improved for chlamydial molecular studies. While several genetic tools have been mainly developed in Chlamydia trachomatis, a stable gene-inducible shuttle vector system has not to date been available for C. psittaci In this study, we adapted a C. trachomatis plasmid shuttle vector system to C. psittaci We constructed a C. psittaci plasmid backbone shuttle vector called pCps-Tet-mCherry. The construct expresses GFP in C. psittaci Importantly, exogeneous genes can be inserted at an MCS and are regulated by a tet promoter. The application of the pCps-Tet-mCherry shuttle vector system enables a promising new approach to investigate unknown gene functions of this pathogen.

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Chlamydia psittaci genetic variants differ in virulence by modulation of host immunity.

Publications

Chlamydia psittaci genetic variants differ in virulence by modulation of host immunity.

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