Unexpected antibiotic susceptibility of a chronic isolate of Coxiella burnetii

Neurotransmitter System-Targeting Drugs Antagonize Growth of the Q Fever Agent, Coxiella burnetii, in Human Cells

Coxiella burnetii is a highly infectious, intracellular, Gram-negative bacterial pathogen that causes human Q fever, an acute flu-like illness that can progress to chronic endocarditis. C. burnetii is transmitted to humans via aerosols and has long been considered a potential biological warfare agent. Although antibiotics, such as doxycycline, effectively treat acute Q fever, a recently identified antibiotic-resistant strain demonstrates the ability of C. burnetii to resist traditional antimicrobials, and chronic disease is extremely difficult to treat with current options. These findings highlight the need for new Q fever therapeutics, and repurposed drugs that target eukaryotic functions to prevent bacterial replication are of increasing interest in infectious disease. To identify this class of anti-C. burnetii therapeutics, we screened a library of 727 FDA-approved or late-stage clinical trial compounds using a human macrophage-like cell model of infection. Eighty-eight compounds inhibited bacterial replication, including known antibiotics, antipsychotic or antidepressant treatments, antihistamines, and several additional compounds used to treat a variety of conditions. The majority of identified anti-C. burnetii compounds target host neurotransmitter system components. Serotoninergic, dopaminergic, and adrenergic components are among the most highly represented targets and potentially regulate macrophage activation, cytokine production, and autophagy. Overall, our screen identified multiple host-directed compounds that can be pursued for potential use as anti-C. burnetii drugs.

IMPORTANCECoxiella burnetii causes the debilitating disease Q fever in humans. This infection is difficult to treat with current antibiotics and can progress to long-term, potentially fatal infection in immunocompromised individuals or when treatment is delayed. Here, we identified many new potential treatment options in the form of drugs that are either FDA approved or have been used in late-stage clinical trials and target human neurotransmitter systems. These compounds are poised for future characterization as nontraditional anti-C. burnetii therapies.

In VitroSusceptibility to Tetracycline and Fluoroquinolones of Japanese Isolates ofCoxiella burnetii

Coxiella burnetii is the agent of the worldwide zoonosis, Q fever. The in vitro susceptibility to tetracycline and fluoroquinolones of Japanese isolates of C. burnetii was evaluated for the first time. The MICs against Japanese isolates were almost the same as the MICs against the foreign reference isolates. The results suggest that the common antibiotics therapy for Q fever used in other countries is also effective for Japanese Q fever patients.

Activity of Telithromycin against Thirteen New Isolates of C. burnetii Including Three Resistant to Doxycycline

In this study we have evaluated the in vitro activity of antibiotics against 13 new isolates of Coxiella burnetii using a real-time quantitative PCR assay. MICs against doxycycline ranged from 1 to 8 microg/mL, telithromycin from 0.5 to 2 microg/mL, and all strains had MICs > or = 8 microg/mL for erythromycin. We report that strains resistant to doxycycline exist either in humans or animals.

Complete genome sequence of the Q-fever pathogen Coxiella burnetii

The 1,995,275-bp genome of Coxiella burnetii, Nine Mile phase I RSA493, a highly virulent zoonotic pathogen and category B bioterrorism agent, was sequenced by the random shotgun method. This bacterium is an obligate intracellular acidophile that is highly adapted for life within the eukaryotic phagolysosome. Genome analysis revealed many genes with potential roles in adhesion, invasion, intracellular trafficking, host-cell modulation, and detoxification. A previously uncharacterized 13-member family of ankyrin repeat-containing proteins is implicated in the pathogenesis of this organism. Although the lifestyle and parasitic strategies of C. burnetii resemble that of Rickettsiae and Chlamydiae, their genome architectures differ considerably in terms of presence of mobile elements, extent of genome reduction, metabolic capabilities, and transporter profiles. The presence of 83 pseudogenes displays an ongoing process of gene degradation. Unlike other obligate intracellular bacteria, 32 insertion sequences are found dispersed in the chromosome, indicating some plasticity in the C. burnetii genome. These analyses suggest that the obligate intracellular lifestyle of C. burnetii may be a relatively recent innovation.

Q fever

Q fever is a zoonosis with a worldwide distribution with the exception of New Zealand. The disease is caused by Coxiella burnetii, a strictly intracellular, gram-negative bacterium. Many species of mammals, birds, and ticks are reservoirs of C. burnetii in nature. C. burnetii infection is most often latent in animals, with persistent shedding of bacteria into the environment. However, in females intermittent high-level shedding occurs at the time of parturition, with millions of bacteria being released per gram of placenta. Humans are usually infected by contaminated aerosols from domestic animals, particularly after contact with parturient females and their birth products. Although often asymptomatic, Q fever may manifest in humans as an acute disease (mainly as a self-limited febrile illness, pneumonia, or hepatitis) or as a chronic disease (mainly endocarditis), especially in patients with previous valvulopathy and to a lesser extent in immunocompromised hosts and in pregnant women. Specific diagnosis of Q fever remains based upon serology. Immunoglobulin M (IgM) and IgG antiphase II antibodies are detected 2 to 3 weeks after infection with C. burnetii, whereas the presence of IgG antiphase I C. burnetii antibodies at titers of >/=1:800 by microimmunofluorescence is indicative of chronic Q fever. The tetracyclines are still considered the mainstay of antibiotic therapy of acute Q fever, whereas antibiotic combinations administered over prolonged periods are necessary to prevent relapses in Q fever endocarditis patients. Although the protective role of Q fever vaccination with whole-cell extracts has been established, the population which should be primarily vaccinated remains to be clearly identified. Vaccination should probably be considered in the population at high risk for Q fever endocarditis.

In vivo endogenous spore formation by Coxiella burnetii in Q fever endocarditis

AIMS

To determine whether Coxiella burnetii, the aetiological agent of Q fever, undergoes endogenous spore-like formation, the crucial stage of the developmental cycle, in the infected cardiac valves of patients with chronic Q fever endocarditis.

METHODS

Surgically removed valves from three cases of Q fever endocarditis were processed for electron microscopy. Sections were stained with potassium permanganate and uranyl acetate before being extensively examined by transmission electron microscopy.

RESULTS

In all three cases endogenous spore-like formation was seen in the infected cardiac valves.

CONCLUSIONS

As the factors that govern sporogenesis in C burnetii are still largely unknown, it is uncertain how important are the implications of the discovery of endogenous spore-like formation in Q fever endocarditis. However, this finding may add new dimensions to current thinking about the treatment of chronic Q fever.

Shell-vial assay: evaluation of a new technique for determining antibiotic susceptibility, tested in 13 isolates of Coxiella burnetii

Coxiella burnetii is a strictly intracellular bacterium. Bacteriostatic effects have been described previously on a few isolates in embryonated eggs (A. J. Spicer, M. G. Peacock, and J. C. Williams, p. 375-383, in W. Burgdorfer and R. L. Anacker, ed., Rickettsiae and rickettsial diseases, 1981). We used the shell-vial technique (D. Raoult, G. Vestris, and M. Enea, J. Clin. Microbiol. 28:2482-2484, 1990) to determine the susceptibility of C. burnetii to amoxicillin, amikacin, erythromycin, co-trimoxazole, pefloxacin, ofloxacin, ciprofloxacin, chloramphenicol, tetracycline, doxycycline, minocycline, and rifampin antibiotics at a single dilution. Human embryonic lung fibroblast monolayers in shell vials were seeded with 13 different C. burnetii isolates, including 3 reference strains (Nine Mile, Q212, and Priscilla) and 10 new isolates, in order to obtain 30% infected cells 6 days later. After inoculation, antibiotics were added, shell vials were incubated for 7 days, and immunofluorescence was revealed and compared with that of the positive controls. Strain Nine Mile was more susceptible than strains Q212 and Priscilla were. The heterogeneity of susceptibility to fluoroquinolones, chloramphenicol, and erythromycin was noted among the strains; all were resistant to amoxicillin and amikacin, and all were susceptible to rifampin, co-trimoxazole, tetracycline, and tetracycline analogs.

Antibiotic treatment of rickettsiosis, recent advances and current concepts

The author reviews the recent advances in the treatment of Mediterranean Spotted Fever and Q fever. In mediterranean spotted fever (M.S.F.), in vitro and preliminary in vivo data support the place of quinolones and josamycin in the treatment of M.S.F. In children josamycin could become the first choice drug as well as in pregnant woman. In Q fever chronic disease should be treated using a combination of antibiotic (doxycycline + quinolones) for a minimum of 3 years.

Pathogenesis of rickettsial infections emphasis on Q fever

The underlying mechanisms at the organismic, cellular and molecular levels that account for rickettsial pathogenesis are beginning to be revealed. In the case of Coxiella burnetii infection, relatively recent genetic and biochemical data, as well as drug susceptibility studies, indicate a correlation between isolate type and clinical disease--chronic or short-term acute. The use of cultured cells as model host systems has revealed that, indeed, different isolates from the major classified strains of C. burnetii cause different host cell responses. Use of this and other models (guinea pigs, mice) have revealed other characteristics and properties of the rickettsiae and the infected hosts and host cells that may account, in part, for acute disease and persistent infection culminating in chronic disease. The virulence factors involved apparently include the agent's surface lipopolysaccharide; other unidentified factors have not been excluded. Molecular cloning will play a major role in elucidating the roles of these factors and in identifying other virulence determinants.

Mechanisms that may account for differential antibiotic susceptibilities among Coxiella burnetii isolates

The Nine Mile, S Q217, and Priscilla isolates, representative of the three major genetic groups of Coxiella burnetii, are known to differ in their susceptibilities to antibiotics. Mechanisms potentially responsible for these differences were investigated. Accumulation of antibiotics by infected L929 cells and purified isolates was measured. In addition, C. burnetii plasmid-transformed Escherichia coli HB101 cells were used to study the possibility that different C. burnetii plasmids are responsible for disparate antibiotic susceptibilities of the isolates. L929 cells recently or persistently infected with the Priscilla isolate exhibited a significantly reduced accumulation of [3H]tetracycline as compared with that in L929 cells infected with either the Nine Mile or S Q217 isolates; accumulation of this drug was greater in cells recently infected each isolate. In contrast, L929 cells recently or persistently infected with the different isolates accumulated [3H]norfloxacin to an equivalent extent. [3H]tetracycline accumulation was approximately the same among the purified isolates. However, as measured by both scintillation and spectrofluorometry, norfloxacin accumulation was significantly diminished in the purified Priscilla isolate. pH had no apparent effect upon isolate permeabilities. The presence of C. burnetii QpH1 or QpRS plasmids did not alter the antibiotic susceptibility of E. coli. Collectively, these results indicate that differential susceptibilities to tetracyclines or fluoroquinolones in C. burnetii isolates may be the result of distinct mechanisms involving altered host-cell (tetracyclines) or isolate-specific (fluoroquinolones) permeabilities.

Comparison of different antibiotic regimens for therapy of 32 cases of Q fever endocarditis

We studied 32 cases of Q fever endocarditis diagnosed in France between January 1985 and December 1989 to evaluate the efficacies of the different regimens of antibiotics used for treatment. Each patient was monitored during the treatment (range, 12 to 60 months), and clinical and biological information was computerized. Various treatments were prescribed, including doxycycline alone (9 cases) or in association with rifampin (4 cases), quinolones (16 cases), or sulfamethoxazole-trimethoprim (1 case). Two patients died before the beginning of the treatment. Nineteen patients had hemodynamic failure and subsequently underwent valve replacement. Nine valve tissue cultures were positive despite previous antibiotic treatment. In terms of their effects on mortality, the difference between doxycycline alone and doxycycline plus quinolones is statistically significant. We conclude that the addition of quinolones to doxycycline is beneficial. On the basis of clinical, serological, and valve tissue culture results, no treatment was able to cure Q fever endocarditis within 2 years, even with a combination of antibiotics. We advise a minimum duration of treatment of 3 years with therapy combining quinolones and doxycycline.