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Q fever pneumonia: virulence of Coxiella burnetii pathovars in a murine model of aerosol infection.

ABSTRACT: Q fever is a worldwide zoonosis caused by Coxiella burnetii, a strictly intracellular bacterium that is a potential bioweapon. Humans usually acquires Q fever after inhalation of dust infected by subclinical animals. We used an aerosol exposure apparatus to challenge immunocompetent (BALB/c) and severe combined immunodeficient (SCID) mice with two different strains (strain Nine Mile and strain Q 212) of C. burnetii at two different inocula. Pathological lesions and dissemination of the bacteria were related to the size of the inoculum. SCID mice showed major pulmonary lesions, whereas similarly infected BALB/c mice were more able to eliminate the bacteria. Pathological differences were found between the strains, with Nine Mile showing more severe histological lesions and quantified spread of bacteria. Our animal model could provide a new tool for the study of acute Q fever pneumonia, the development of Q fever in immunodeficient hosts, and the differentiation of pathogenicity among C. burnetii isolates.

SUBMITTER: Stein A

PROVIDER: S-EPMC1087393 | biostudies-literature | 2005 Apr

REPOSITORIES: biostudies-literature

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Q fever pneumonia: virulence of Coxiella burnetii pathovars in a murine model of aerosol infection.

Stein Andreas A Louveau Céline C Lepidi Hubert H Ricci Fanny F Baylac Pascal P Davoust Bernard B Raoult Didier D

Infection and immunity 20050401 4

Q fever is a worldwide zoonosis caused by Coxiella burnetii, a strictly intracellular bacterium that is a potential bioweapon. Humans usually acquires Q fever after inhalation of dust infected by subclinical animals. We used an aerosol exposure apparatus to challenge immunocompetent (BALB/c) and severe combined immunodeficient (SCID) mice with two different strains (strain Nine Mile and strain Q 212) of C. burnetii at two different inocula. Pathological lesions and dissemination of the bacteria ...[more]

PMID: 15784593

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Project description:Coxiella burnetii requires a type IVB secretion system (T4SS) to promote intracellular replication and virulence. We hypothesized that Coxiella employs its T4SS to secrete effectors that enable stealthy colonization of immune cells. To address this, we used RNA sequencing to compare the transcriptional response of murine bone marrow-derived macrophages (BMDM) infected with those of wild-type Coxiella and a T4SS-null mutant at 8 and 24 h postinfection. We found a T4SS-independent upregulation of proinflammatory transcripts which was consistent with a proinflammatory polarization phenotype. Despite this, infected BMDM failed to completely polarize, as evidenced by modest surface expression of CD38 and CD11c, nitrate production, and reduced proinflammatory cytokine and chemokine secretion compared to positive controls. As these BMDM permitted replication of C. burnetii, we employed them to identify T4SS effectors that are essential in the specific cellular context of a primary macrophage. We found five Himar1 transposon mutants in T4SS effectors that had a replication defect in BMDM but not J774A.1 cells. The mutants were also attenuated in a SCID mouse model of infection. Among these candidate virulence factors, we found that CBU1639 contributed to the inhibition of macrophage proinflammatory responses to Coxiella infection. These data demonstrate that while T4SS is dispensable for the stealthy invasion of primary macrophages, Coxiella has evolved multiple T4SS effectors that specifically target macrophage function to proliferate within that specific cellular context. IMPORTANCE Coxiella burnetii, the causative agent of Q fever, preferentially infects macrophages of the respiratory tract when causing human disease. This work describes how primary macrophages respond to C. burnetii at the earliest stages of infection, before bacterial replication. We found that while infected macrophages increase expression of proinflammatory genes after bacterial entry, they fail to activate the accompanying antibacterial functions that might ultimately control the infection. This disconnect between initial response and downstream function was not mediated by the bacterium's type IVB secretion system, suggesting that Coxiella has other virulence factors that dampen host responses early in the infection process. Nevertheless, we were able to identify several type IVB secreted effectors that were specifically required for survival in macrophages and mice. This work is the first to identify type IVB secretion effectors that are specifically required for infection and replication within primary macrophages.

Project description:Coxiella burnetii strains carry one of four large, conserved, autonomously replicating plasmids (QpH1, QpRS, QpDV, and QpDG) or a QpRS-like chromosomally integrated sequence of unknown function. Here we report the characterization of the QpH1 plasmid of C. burnetii Nine Mile phase II by making QpH1-deficient strains. A shuttle vector pQGK containing the CBUA0036-0039a region (predicted as being required for the QpH1 maintenance) was constructed. The pQGK vector can be stably transformed into the Nine Mile II and maintained at a similar low copy like QpH1. Importantly, transformation with pQGK cured the endogenous QpH1 due to plasmid incompatibility. Compared to a Nine Mile II transformant of a RSF1010-ori based vector, the pQGK transformant shows a similar growth curve in both axenic media and Buffalo green monkey kidney cells, a variable growth defect in macrophage-like THP-1 cells depending on the origin of inoculum, and dramatically reduced ability of colonizing wild-type bone marrow-derived murine macrophages. Furthermore, we found CBUA0037-0039 ORFs are essential for plasmid maintenance, and CBUA0037-0038 ORFs account for plasmid compatibility. And plasmid-deficient C. burnetii can be isolated by using CBUA0037 or -0038 deletion vectors. Furthermore, QpH1-deficient C. burnetii strains caused a lesser extent of splenomegaly in SCID mice but, intriguingly, they had significant growth in SCID mouse-sourced macrophages. Taken together, our data suggest that QpH1 encodes factor(s) essential for colonizing murine, not human, macrophages. This study suggests a critical role of QpH1 for C. burnetii persistence in rodents and expands the toolkit for the genetic studies in C. burnetiiAuthor summary All C. burnetii isolates carry one of four large, conserved, autonomously replicating plasmids or a plasmid-like chromosomally integrated sequence. The plasmid is a candidate virulence factor of unknown function. Here we describe the construction of novel shuttle vectors that allow making plasmid-deficient C. burnetii mutants. With this plasmid-curing approach, we characterized the role of the QpH1 plasmid in in vitro and in vivoC. burnetii infection models. We found that the plasmid plays a critical role for C. burnetii growth in murine macrophages. Our work suggests an essential role of the QpH1 plasmid for the acquisition of colonizing capability in rodents by C. burnetii This study represents a major step toward unravelling the mystery of the C. burnetii cryptic plasmids.

Dataset Information

Q fever pneumonia: virulence of Coxiella burnetii pathovars in a murine model of aerosol infection.

Publications

Q fever pneumonia: virulence of Coxiella burnetii pathovars in a murine model of aerosol infection.

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