Identification and Characterization of an HtrA Sheddase Produced by Coxiella burnetii

Having previously shown that soluble E-cadherin (sE-cad) is found in sera of Q fever patients and that infection of BeWo cells by C. burnetii leads to modulation of the E-cad/β-cat pathway, our purpose was to identify which sheddase(s) might catalyze the cleavage of E-cad. Here, we searched for a direct mechanism of cleavage initiated by the bacterium itself, assuming the possible synthesis of a sheddase encoded in the genome of C. burnetii or an indirect mechanism based on the activation of a human sheddase. Using a straightforward bioinformatics approach to scan the complete genomes of four laboratory strains of C. burnetii, we demonstrate that C. burnetii encodes a 451 amino acid sheddase (CbHtrA) belonging to the HtrA family that is differently expressed according to the bacterial virulence. An artificial CbHtrA gene (CoxbHtrA) was expressed, and the CoxbHtrA recombinant protein was found to have sheddase activity. We also found evidence that the C. burnetii infection triggers an over-induction of the human HuHtrA gene expression. Finally, we demonstrate that cleavage of E-cad by CoxbHtrA on macrophages-THP-1 cells leads to an M2 polarization of the target cells and the induction of their secretion of IL-10, which "disarms" the target cells and improves C. burnetii replication. Taken together, these results demonstrate that the genome of C. burnetii encodes a functional HtrA sheddase and establishes a link between the HtrA sheddase-induced cleavage of E-cad, the M2 polarization of the target cells and their secretion of IL-10, and the intracellular replication of C. burnetii.

Seroreactivity to Coxiella burnetii in an Agricultural Population and Prevalence of Coxiella burnetii Infection in Ticks of a Non-Endemic Region for Q Fever in South Korea

Coxiella burnetii infects humans and wild and domesticated animals. Although reported cases on Jeju Island, off the coast of South Korea, are rare, the region is considered to have a high potential for Q fever. We investigated the seroprevalence of antibodies to C. burnetii in 230 farmers living in ten rural areas on Jeju Island between January 2015 and December 2019. Blood samples were collected and examined for C. burnetii Phase I/II IgM and IgG antibodies. Trained researchers collected ticks from rural areas. Clone XCP-1 16S ribosomal RNA gene sequencing was performed to identify Coxiella species from the collected ticks. The overall seroprevalence of antibodies to C. burnetii in farmers was 35.7%. The seroprevalence was significantly higher in fruit farmers. Of the collected ticks, 5.4% (19/351) of the Haemaphysalis longicornis ticks harbored C. burnetti. A high seroprevalence of antibodies to C. burnetii was observed in this region of Jeju Island, confirming that C. burnetti is endemic. Physicians should thus consider Q fever in the differential diagnosis of patients that present with acute fever after participating in outdoor activities.

In the Search of Potential Serodiagnostic Proteins to Discriminate Between Acute and Chronic Q Fever in Humans. Some Promising Outcomes

Coxiella burnetii is the agent that causes acute and chronic Q fever infections in humans. Although the isolates studied so far have shown that the two forms of the disease differ in virulence potential thus, implying a variance in their proteomic profile, the methods used do not deliver enough discriminatory capability and often, human infections may be mis-diagnosed. The current study adds further knowledge to the results that we have already published on the Coxiella outer membrane protein 1 (Com1). Herein we identified the proteins GroEL, Ybgf, OmpH, and UPF0422 as candidates for serodiagnostics of Q fever; following cloning, expression and purification they were further used as antigens in ELISA for the screening of patients' sera associated with chronic Q fever endocarditis, sera negative for phase I IgG, sera with at least one sample positive for phase I IgG and sera from patients who suffered from various rheumatic diseases. Blood donors were used as the controls. Sensitivity, specificity, positive predictive value, negative predictive value, and Cohen's kappa coefficient (κ) were calculated and we also performed binary logistic regression analysis to identify combinations of proteins with increased diagnostic yield. We found that proteins GroEL and Ybgf, together with Com1, play the most significant role in the correct diagnosis of chronic Q fever. Of these three proteins, it was shown that Com1 and GroEL present the highest sensitivity and specificity altogether. The results add to the existing knowledge that an antigen-based serodiagnostic test that will be able to correctly diagnose chronic Q fever may not be far from reality.

Coxiella burnetii: international pathogen of mystery

Coxiella burnetii is an intracellular bacterium that causes acute and chronic Q fever. This unique pathogen has been historically challenging to study due to obstacles in genetically manipulating the organism and the inability of small animal models to fully mimic human Q fever. Here, we review the current state of C. burnetii research, highlighting new approaches that allow the mechanistic study of infection in disease relevant settings.

Development of a Coxiella burnetii culture method for high-throughput assay to identify host-directed therapeutics

The intracellular Gram-negative bacterium, Coxiella burnetii, is a worldwide zoonotic pathogen and the causative agent of Q fever. The standard of care for C. burnetii infections involves extended periods of antibiotic treatment and the development of doxycycline-resistant strains stress the need for new treatment strategies. A previously developed axenic medium has facilitated in vitro growth of the organism. In this study, we have developed a simple culture method that is inexpensive, reliable and utilizes a modular hypoxic chamber system for either small or large scale production of bacteria without the need of a tri-gas incubator. This method provides consistent growth and yields sufficient viable bacteria within four days of culture and can be used for high-throughput screening. The viable bacteria were quantified by counting colony forming units and total bacteria were enumerated using a genomic equivalent method. The characterized bacterial inoculum was then used to optimize cell-based high-throughput immunofluorescence assays with a goal to quantify intracellular bacteria and then screen and identify compounds that inhibit early stages of C. burnetii infection in macrophages.

Seroprevalence of Coxiella burnetii (Q fever) Exposure in Humans on Reunion Island

After the documentation of sporadic cases of Q fever endocarditis, we conducted a serosurvey to assess Coxiella burnetii exposure on Reunion Island. Two hundred forty-one stored frozen human sera were analyzed using an immunofluorescence assay. The weighted seroprevalence of Q fever was of 6.81% (95% confidence interval, 4.02%–9.59%). Despite the absence of infection in youths <20 years of age, exposure was not driven by age or by gender. There was a spatial disparity in exposure across the island, with higher prevalence being reported in regions where ruminant farms are present. The seroprevalence pattern suggests that Q fever is endemic on Reunion Island.

Unusual presentation of Q fever in a kidney-pancreas transplant recipient

Q fever is uncommon in solid organ transplant (SOT) recipients. We describe a case of granulomatous lung disease as an unusual presentation of chronic Q fever in a kidney-pancreas transplant recipient.

Clinical Features and Complications of Coxiella burnetii Infections From the French National Reference Center for Q Fever

IMPORTANCE

Q fever remains widespread throughout the world; the disease is serious and causes outbreaks and deaths when complications are not detected. The diagnosis of Q fever requires the demonstration of the presence of Coxiella burnetii and the identification of an organic lesion.

OBJECTIVE

To describe the hitherto neglected clinical characteristics of Q fever and identifying risk factors for complications and death.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cohort study conducted from January 1, 1991, through December 31, 2016, included patients treated at the French National Reference Center for Q fever with serologic findings positive for C burnetii and clinical data consistent with C burnetii infection. Clinical data were prospectively collected by telephone. Patients with unavailable clinical data or an unidentified infectious focus were excluded.

MAIN OUTCOMES AND MEASURES

Q fever complications and mortality.

RESULTS

Of the 180 483 patients undergoing testing, 2918 had positive findings for C burnetii and 2434 (68.8% men) presented with clinical data consistent with a C burnetii infection. Mean (SD) age was 51.8 (17.4) years, and the ratio of men to women was 2.2. At the time of inclusion, 1806 patients presented with acute Q fever, including 138 with acute Q fever that progressed to persistent C burnetii infection, and 766 had persistent focalized C burnetii infection. Rare and hitherto neglected foci of infections included lymphadenitis (97 [4.0%]), acute Q fever endocarditis (50 [2.1%]), hemophagocytic syndrome (9 [0.4%]), and alithiasic cholecystitis (11 [0.4%]). Vascular infection (hazard ratio [HR], 3.1; 95% CI, 1.7-5.7; P < .001) and endocarditis (HR, 2.4; 95% CI, 1.1-5.1; P = .02) were associated with an increased risk of death. Independent indicators of lymphoma were lymphadenitis (HR, 77.4; 95% CI, 21.2-281.8; P < .001) and hemophagocytic syndrome (HR, 19.1; 95% CI, 3.4-108.6; P < .001). The presence of anticardiolipin antibodies during acute Q fever has been associated with several complications, including hepatitis, cholecystitis, endocarditis, thrombosis, hemophagocytic syndrome, meningitis, and progression to persistent endocarditis.

CONCLUSIONS AND RELEVANCE

Previously neglected foci of C burnetii infection include the lymphatic system (ie, bone marrow, lymphadenitis) with a risk of lymphoma. Cardiovascular infections were the main fatal complications, highlighting the importance of routine screening for valvular heart disease and vascular anomalies during acute Q fever. Routine screening for anticardiolopin antibodies during acute Q fever can help prevent complications. Positron emission tomographic scanning could be proposed for all patients with suspected persistent focused infection to rapidly diagnose vascular and lymphatic infections associated with death and lymphoma, respectively.