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

Efficacy of rifapentine and other rifamycins against Coxiella burnetii in vitro

Since 1999, doxycycline and hydroxychloroquine have been the recommended treatment for chronic Q fever, a life-threatening disease caused by the bacterial pathogen, Coxiella burnetii. Despite the duration of its use, the treatment is not ideal due to the lengthy treatment time, high mortality rate, resistant strains, and the potential for contraindicated usage. A literature search was conducted to identify studies that screened large panels of drugs against C. burnetii to identify novel targets with potential efficacy against C. burnetii. Twelve candidate antimicrobials approved for use in humans by the US Food and Drug Administration were selected and minimum inhibitory concentrations (MICs) were determined against the low virulence strain Nine Mile phase II. Rifabutin and rifaximin were the best performing antibiotics tested with MICs of ≤0.01 µg mL-1. Further screening of these top candidates was conducted alongside two drugs from the same class, rifampin, well-characterized, and rifapentine, not previously reported against C. burnetii. These were screened against virulent strains of C. burnetii representing three clinically relevant genotypes. Rifapentine was the most effective in the human monocytic leukemia cell line, THP-1, with a MIC ≤0.01 µg mL-1. In the human kidney epithelial cell line, A-498, efficacy of rifapentine, rifampin, and rifabutin varied across C. burnetii strains with MICs between ≤0.001 and 0.01 µg mL-1. Rifampin, rifabutin, and rifapentine were all bactericidal against C. burnetii; however, rifabutin and rifapentine demonstrated impressive bactericidal activity as low as 0.1 µg mL-1 and should be further explored as alternative Q fever treatments given their efficacy in vitro.

IMPORTANCE

This work will help inform investigators and physicians about potential alternative antimicrobial therapies targeting the causative agent of Q fever, Coxiella burnetii. Chronic Q fever is difficult to treat, and alternative antimicrobials are needed. This manuscript explores the efficacy of rifamycin antibiotics against virulent strains of C. burnetii representing three clinically relevant genotypes in vitro. Importantly, this study determines the susceptibility of C. burnetii to rifapentine, which has not been previously reported. Evaluation of the bactericidal activity of the rifamycins reveals that rifabutin and rifapentine are bactericidal at low concentrations, which is unusual for antibiotics against C. burnetii.

Treatment of persistent focalized Q fever: time has come for an international randomized controlled trial

Q fever is a worldwide zoonosis due to Coxiella burnetii, responsible for endocarditis and endovascular infections. Since the 1990s, the combination hydroxychloroquine + doxycycline has constituted the curative and prophylactic treatment in persistent focalized Q fever. This combination appears to have significantly reduced the treatment's duration (from 60 to 26 months), yet substantial evidence of effectiveness remains lacking. Data are mostly based on in vitro and observational studies. We conducted a literature review to assess the effectiveness of this therapy, along with potential alternatives. The proposed in vitro mechanism of action describes the inhibition of Coxiella replication by doxycycline through the restoration of its bactericidal activity (inhibited in acidic environment) by alkalinization of phagolysosome-like vacuoles with hydroxychloroquine. So far, the rarity and heterogeneous presentation of cases have made it challenging to design prospective studies with statistical power. The main studies supporting this treatment are retrospective cohorts, dating back to the 1990s-2000s. Retrospective studies from the large Dutch outbreak of Q fever (>4000 cases between 2007 and 2010) did not corroborate a clear benefit of this combination, notably in comparison with other regimens. Thus, there is still no consensus among the medical community on this issue. However insufficient the evidence, today the doxycycline + hydroxychloroquine combination remains the regimen with the largest clinical experience in the treatment of 'chronic' Q fever. Reinforcing the guidelines' level of evidence is critical. We herein propose the creation of an extensive international registry, followed by a prospective cohort or ideally a randomized controlled trial.

Antimicrobial resistance gene lack in tick-borne pathogenic bacteria

Tick-borne infections, including those of bacterial origin, are significant public health issues. Antimicrobial resistance (AMR), which is one of the most pressing health challenges of our time, is driven by specific genetic determinants, primarily by the antimicrobial resistance genes (ARGs) of bacteria. In our work, we investigated the occurrence of ARGs in the genomes of tick-borne bacterial species that can cause human infections. For this purpose, we processed short/long reads of 1550 bacterial isolates of the genera Anaplasma (n = 20), Bartonella (n = 131), Borrelia (n = 311), Coxiella (n = 73), Ehrlichia (n = 13), Francisella (n = 959) and Rickettsia (n = 43) generated by second/third generation sequencing that have been freely accessible at the NCBI SRA repository. From Francisella tularensis, 98.9% of the samples contained the FTU-1 beta-lactamase gene. However, it is part of the F. tularensis representative genome as well. Furthermore, 16.3% of them contained additional ARGs. Only 2.2% of isolates from other genera (Bartonella: 2, Coxiella: 8, Ehrlichia: 1, Rickettsia: 2) contained any ARG. We found that the odds of ARG occurrence in Coxiella samples were significantly higher in isolates related to farm animals than from other sources. Our results describe a surprising lack of ARGs in these bacteria and suggest that Coxiella species in farm animal settings could play a role in the spread of AMR.

Evaluation of the Efficacy of Doxycycline, Ciprofloxacin, Levofloxacin and Co-trimoxazole using in vitro and in vivo models of Q fever

Q fever, caused by the intracellular pathogen Coxiella burnetii, is traditionally treated using tetracycline antibiotics, such as doxycycline. Doxycycline is often poorly tolerated and antibiotic resistant strains have been isolated. In this study, we have evaluated a panel of antibiotics (doxycycline, ciprofloxacin, levofloxacin, and, co-trimoxazole) against C. burnetii using in vitro methods (determination of MIC using liquid and solid media; efficacy assessment in a THP cell infection model) and in vivo methods (wax moth larvae and mouse models of infection). In addition, the schedule for antibiotic treatment has been evaluated, with therapy initiated at 24 h pre or post challenge. Both doxycycline and levofloxacin limited overt clinical signs during treatment in the AJ mouse model of aerosol infection, but further studies are required to investigate the possibility of disease relapse or incomplete bacterial clearance after the antibiotics are stopped. Levofloxacin was well tolerated and therefore warrants further investigation as an alternative to the current recommended treatment with doxycycline.

Q Fever Osteoarticular Infection in Children

Studies of this condition, which is underestimated in children, will aid in its diagnosis and treatment.

Q fever osteoarticular infection in children is an underestimated disease. We report 3 cases of Q fever osteomyelitis in children and review all cases reported in the literature through March 2018. A high index of suspicion is encouraged in cases of an unusual manifestation, prolonged course, relapsing symptoms, nonresolving or slowly resolving osteomyelitis, culture-negative osteomyelitis, or bone histopathology demonstrating granulomatous changes. Urban residence or lack of direct exposure to animals does not rule out infection. Diagnosis usually requires use of newer diagnostic modalities. Optimal antimicrobial therapy has not been well established; some case-patients may improve spontaneously or during treatment with a β-lactam. The etiology of treatment failure and relapse is not well understood, and tools for follow-up are lacking. Clinicians should be aware of these infections in children to guide optimal treatment, including choice of antimicrobial drugs, duration of therapy, and methods of monitoring response to treatment..

From Q Fever to Coxiella burnetii Infection: a Paradigm Change

Coxiella burnetii is the agent of Q fever, or "query fever," a zoonosis first described in Australia in 1937. Since this first description, knowledge about this pathogen and its associated infections has increased dramatically. We review here all the progress made over the last 20 years on this topic. C. burnetii is classically a strict intracellular, Gram-negative bacterium. However, a major step in the characterization of this pathogen was achieved by the establishment of its axenic culture. C. burnetii infects a wide range of animals, from arthropods to humans. The genetic determinants of virulence are now better known, thanks to the achievement of determining the genome sequences of several strains of this species and comparative genomic analyses. Q fever can be found worldwide, but the epidemiological features of this disease vary according to the geographic area considered, including situations where it is endemic or hyperendemic, and the occurrence of large epidemic outbreaks. In recent years, a major breakthrough in the understanding of the natural history of human infection with C. burnetii was the breaking of the old dichotomy between "acute" and "chronic" Q fever. The clinical presentation of C. burnetii infection depends on both the virulence of the infecting C. burnetii strain and specific risks factors in the infected patient. Moreover, no persistent infection can exist without a focus of infection. This paradigm change should allow better diagnosis and management of primary infection and long-term complications in patients with C. burnetii infection.

Current and past strategies for bacterial culture in clinical microbiology

A pure bacterial culture remains essential for the study of its virulence, its antibiotic susceptibility, and its genome sequence in order to facilitate the understanding and treatment of caused diseases. The first culture conditions empirically varied incubation time, nutrients, atmosphere, and temperature; culture was then gradually abandoned in favor of molecular methods. The rebirth of culture in clinical microbiology was prompted by microbiologists specializing in intracellular bacteria. The shell vial procedure allowed the culture of new species of Rickettsia. The design of axenic media for growing fastidious bacteria such as Tropheryma whipplei and Coxiella burnetii and the ability of amoebal coculture to discover new bacteria constituted major advances. Strong efforts associating optimized culture media, detection methods, and a microaerophilic atmosphere allowed a dramatic decrease of the time of Mycobacterium tuberculosis culture. The use of a new versatile medium allowed an extension of the repertoire of archaea. Finally, to optimize the culture of anaerobes in routine bacteriology laboratories, the addition of antioxidants in culture media under an aerobic atmosphere allowed the growth of strictly anaerobic species. Nevertheless, among usual bacterial pathogens, the development of axenic media for the culture of Treponema pallidum or Mycobacterium leprae remains an important challenge that the patience and innovations of cultivators will enable them to overcome.

Etiologies of illness among patients meeting integrated management of adolescent and adult illness district clinician manual criteria for severe infections in northern Tanzania: implications for empiric antimicrobial therapy

We describe the laboratory-confirmed etiologies of illness among participants in a hospital-based febrile illness cohort study in northern Tanzania who retrospectively met Integrated Management of Adolescent and Adult Illness District Clinician Manual (IMAI) criteria for septic shock, severe respiratory distress without shock, and severe pneumonia, and compare these etiologies against commonly used antimicrobials, including IMAI recommendations for emergency antibacterials (ceftriaxone or ampicillin plus gentamicin) and IMAI first-line recommendations for severe pneumonia (ceftriaxone and a macrolide). Among 423 participants hospitalized with febrile illness, there were 25 septic shock, 37 severe respiratory distress without shock, and 109 severe pneumonia cases. Ceftriaxone had the highest potential utility of all antimicrobials assessed, with responsive etiologies in 12 (48%) septic shock, 5 (14%) severe respiratory distress without shock, and 19 (17%) severe pneumonia illnesses. For each syndrome 17-27% of participants had etiologic diagnoses that would be non-responsive to ceftriaxone, but responsive to other available antimicrobial regimens including amphotericin for cryptococcosis and histoplasmosis; anti-tuberculosis therapy for bacteremic disseminated tuberculosis; or tetracycline therapy for rickettsioses and Q fever. We conclude that although empiric ceftriaxone is appropriate in our setting, etiologies not explicitly addressed in IMAI guidance for these syndromes, such as cryptococcosis, histoplasmosis, and tetracycline-responsive bacterial infections, were common.

Draft genome sequence of Coxiella burnetii Dog Utad, a strain isolated from a dog-related outbreak of Q fever

Coxiella burnetii Dog Utad, with a 2 008 938 bp genome is a strain isolated from a parturient dog responsible for a human familial outbreak of acute Q fever in Nova Scotia, Canada. Its genotype, determined by multispacer typing, is 21; the only one found in Canada that includes Q212, which causes endocarditis. Only 107 single nucleotide polymorphisms and 16 INDELs differed from Q212, suggesting a recent clonal radiation.

Comparison of Japanese Isolates ofCoxiella burnetiiby PCR-RFLP and Sequence Analysis

The genetic variation of Japanese isolates of Coxiella burnetii, the agent of Q fever, was found for the first time. Forty-nine out of 72 isolates had the chronic pattern of the isocitrate hydrogenase gene. Sequence analysis revealed that the isolates have a specific nucleotide sequence. The putative amino acid sequence was the same as that of chronic reference strains. These results suggest the variation of C. burnetii isolates in Japan.

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.

Antimicrobial therapies for Q fever

Q fever is caused by the bacterium Coxiella burnetii and has both acute and chronic forms. The acute disease is a febrile illness often with headache and myalgia that can be self-limiting, whereas the chronic disease typically presents as endocarditis and can be life threatening. The normal therapy for the acute disease is a 2 week course of doxycycline, whereas chronic disease requires 18-24 months of doxycycline in combination with hydroxychloroquine. Alternative treatments are used for pregnant women, young children and those who cannot tolerate doxycycline. Doxycycline resistance is rare, but has been reported. Co-trimoxazole is a currently recommended alternative treatment, but quinolones, rifampin and newer macrolides may also provide some benefit.

A Q Fever Outbreak in the Netherlands: Consequences for Tissue Banking

BACKGROUND: Emerging infectious diseases can compromise the safety of tissues for transplantations. A recent outbreak of Q fever, a zoonosis caused by the bacterium Coxiella burnetii, in the Netherlands compelled the Dutch tissue banks to assess the risk of Q fever transmission through tissue transplantation in order to maintain optimal safety. MATHODS: This article describes the systematic approach that was followed in the Netherlands. This approach included a review of the literature, a qualitative risk assessment, expert opinion gathering and investigations for specific strategies that can help to maintain the balance between tissue safety and availability. RESULTS: This resulted in a specific donor selection policy and in development of further research to fill in gaps in knowledge about Q fever in tissue transplantation. CONCLUSION: The strategy described in this article may be useful for tissue bankers facing similar outbreaks of emerging infections or may be useful for development of future guidelines or assessment strategies for tissue banking.

Antibiotic susceptibility and intracellular localization of Diplorickettsia massiliensis

Diplorickettsia massiliensis is an obligate intracellular bacterium from the Coxiellaceae family recently isolated from Ixodes ricinus ticks. The inhibitory effects of antimicrobial agents were assessed by two different methods, immunofluorescence and Gimenez staining assay. Different markers (EEA1, Lamp-1, Cathepsin D, and LysoTracker Red DND99) were used to reveal the nature of the vacuole containing the bacterium. Ciprofloxacin, levofloxacin, and rifampin had MIC values of 2 lg mL(-1). We found that 4 lg mL(-1) of Doxycycline inhibited the growth of D. massiliensis strain. Surprisingly, D. massiliensis was resistant to chloramphenicol up to the concentration of 64 lg mL(-1). We found that penicillin G, ammonium chloride, gentamycin, omeprazole, bafilomycin A1, and chloroquine were not active against D. massiliensis. Studies performed with markers EEA1, Lamp-1, Cathepsin D, and LysoTracker Red DND99 showed that D. massiliensis is localized within an acidic compartment that is not an early phagosome, but a late phagosome or a phagolysosome. Gimenez staining stays a good method that will work with a very low number of bacteria and can be used to determine the MICs of new therapeutic antibiotics precisely. The resistance profile of D. massiliensis was found to be quite unusual for intracellular Gram-negative bacterium with marked resistance to chloramphenicol. Despite of localization in acidic compartment, pH-neutralizing agents do not significantly inhibit intracellular growth of bacterium. The results of these studies prove that antibiotic resistance does not depend on pH of vacuole. This pH-related mechanism seems not to play a contributing role in the overall resistance of D. massiliensis.

DNA gyrase and topoisomerase IV mutations in an in vitro fluoroquinolone-resistant Coxiella burnetii strain

The etiological agent of Q fever, Coxiella burnetii, is an obligate intracellular bacterium that multiplies within a vacuole with lysosomal characteristics. Quinolones have been used as an alternative therapy for Q fever. In this study, quinolone-resistance-determining regions of the genes coding for DNA gyrase and topoisomerase IV were analyzed by DNA sequencing from an in vitro fluoroquinolone-resistant C. burnetii strain (Q212). Sequencing and aligning of DNA gyrase encoding genes (gyrA and gyrB) and topoisomerase IV genes (parC and parE) revealed one gyrA mutation leading to the amino acid substitution Asp87Gly (Escherichia coli numbering), two gyrB mutations leading to the amino acid substitutions Ser431Pro and Met518Ile, and three parC mutations leading to the amino acid substitutions Asp69Asn, Thr80Ile, and Gly104Ser. The corresponding alignment of the C. burnetii Q212 reference strain, the in vitro developed fluoroquinolone-resistant C. burnetii Q212 strain, and E. coli resulted in the identification of several other naturally occurring mutations within and outside the quinolone-resistance-determining regions of C. burnetii providing indications of possible natural resistance to fluoroquinolones. The present study adds additional potential mutations in the DNA topoisomerases that may be involved in fluoroquinolone resistance in C. burnetii due to their previous characterization in other bacterial species.

[Infection by Coxiella burnetii (Q fever)]

In spite of being described over 60 years, Q fever is still a little known disease. The exact prevalence is also unknown, but probably the number of cases of Q fever is underestimated. There is much variation in the clinical presentation, including severe forms with a poor prognosis. Acute cases often present as an asymptomatic infection, flu-like syndrome, pneumonia or hepatitis. Presumably, host factors play an important role in the development of chronic disease, which may present as endocarditis with negative blood culture. The diagnosis of Q fever should be considered in cases of fever of unknown origin, especially if the subject has been in contact with mammals suspicious to be infected. The best methods of microbiological diagnosis are those that allow direct detection of bacteria (cell culture and PCR), although these procedures should be performed in laboratories with adequate biosafety measures, and with specialized personnel. For serologícal diagnosis, the reference method is indirect immunofluorescence (IIF), which is very sensitive and specific. In suspected cases of acute Q fever, diagnosis should be confirmed by serum titers (IgG and/or IgM), obtained by immunofluorescence above the cutoff calculated for each geographic area, or by seroconversion.

Azithromycin for acute Q fever in pregnancy

Q fever is a zoonosis caused by Coxiella burnetii. Although data on Q fever during pregnancy are limited, they indicate that infection with C. burnetii is associated with high morbidity and mortality. The infection is usually asymptomatic in pregnant women but may result in obstetric complications such as spontaneous abortion, intrauterine growth retardation, intrauterine fetal death and premature delivery; in addition, pregnant women are at higher risk of developing chronic Q fever. Treatment of Q fever during pregnancy is challenging not only because C. burnetii is an intracellular bacterium but also because of safety restrictions and limited information on the efficacy of treatment. We report a case of acute Q fever in pregnancy with a successful outcome for mother and child, describe our therapeutic approach to the management of this case, and suggest that treatment with azithromycin may have prevented possible obstetric complications and evolution toward a chronic serologic profile in our patient.

Bacteriostatic and bactericidal activities of tigecycline against Coxiella burnetii and comparison with those of six other antibiotics

The present article is a study of the in vitro susceptibility of eight Greek Coxiella burnetii isolates, derived from patients with acute Q fever, and two reference strains of Coxiella burnetii to tigecycline. The bacteriostatic activity of tigecycline was compared with those of six other antibiotics using a shell vial assay. The MICs of the examined antibiotics were as follows: tigecycline ranged from 0.25 to 0.5 microg/ml; doxycycline, trovafloxacin, and ofloxacin ranged from 1 to 2 microg/ml; linezolid and clarithromycin ranged from 2 to 4 microg/ml; and ciprofloxacin ranged from 4 to 8 microg/ml. Tigecycline was effective in inhibiting the infection of Vero cells by C. burnetii. No bactericidal activity was observed against C. burnetii at 4 microg/ml.

Characterization of a Coxiella burnetii ftsZ mutant generated by Himar1 transposon mutagenesis

Coxiella burnetii is a gram-negative obligate intracellular bacterium and the causative agent of human Q fever. The lack of methods to genetically manipulate C. burnetii significantly impedes the study of this organism. We describe here the cloning and characterization of a C. burnetii ftsZ mutant generated by mariner-based Himar1 transposon (Tn) mutagenesis. C. burnetii was coelectroporated with a plasmid encoding the Himar1 C9 transposase variant and a plasmid containing a Himar1 transposon encoding chloramphenicol acetyltransferase, mCherry fluorescent protein, and a ColE1 origin of replication. Vero cells were infected with electroporated C. burnetii and transformants scored as organisms replicating in the presence of chloramphenicol and expressing mCherry. Southern blot analysis revealed multiple transpositions in the C. burnetii genome and rescue cloning identified 30 and 5 insertions in coding and noncoding regions, respectively. Using micromanipulation, a C. burnetii clone was isolated containing a Tn insertion within the C terminus of the cell division gene ftsZ. The ftsZ mutant had a significantly lower growth rate than wild-type bacteria and frequently appeared as filamentous forms displaying incomplete cell division septa. The latter phenotype correlated with a deficiency in generating infectious foci on a per-genome basis compared to wild-type organisms. The mutant FtsZ protein was also unable to bind the essential cell division protein FtsA. This is the first description of C. burnetii harboring a defined gene mutation generated by genetic transformation.

Laboratory maintenance of Rickettsia rickettsii

This unit includes protocols for the laboratory maintenance of the obligate intracellular bacterium Rickettsia rickettsii, including propagation in mammalian cell cultures, as well as isolation, counting, and storage procedures. Regulations for working with R. rickettsii in biosafety level 3 containment are also discussed.

A bioinformatic approach to understanding antibiotic resistance in intracellular bacteria through whole genome analysis

Intracellular bacteria survive within eukaryotic host cells and are difficult to kill with certain antibiotics. As a result, antibiotic resistance in intracellular bacteria is becoming commonplace in healthcare institutions. Owing to the lack of methods available for transforming these bacteria, we evaluated the mechanisms of resistance using molecular methods and in silico genome analysis. The objective of this review was to understand the molecular mechanisms of antibiotic resistance through in silico comparisons of the genomes of obligate and facultative intracellular bacteria. The available data on in vitro mutants reported for intracellular bacteria were also reviewed. These genomic data were analysed to find natural mutations in known target genes involved in antibiotic resistance and to look for the presence or absence of different resistance determinants. Our analysis revealed the presence of tetracycline resistance protein (Tet) in Bartonella quintana, Francisella tularensis and Brucella ovis; moreover, most of the Francisella strains possessed the blaA gene, AmpG protein and metallo-beta-lactamase family protein. The presence or absence of folP (dihydropteroate synthase) and folA (dihydrofolate reductase) genes in the genome could explain natural resistance to co-trimoxazole. Finally, multiple genes encoding different efflux pumps were studied. This in silico approach was an effective method for understanding the mechanisms of antibiotic resistance in intracellular bacteria. The whole genome sequence analysis will help to predict several important phenotypic characteristics, in particular resistance to different antibiotics. In the future, stable mutants should be obtained through transformation methods in order to demonstrate experimentally the determinants of resistance in intracellular bacteria.

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.

Correlation between ratio of serum doxycycline concentration to MIC and rapid decline of antibody levels during treatment of Q fever endocarditis

Endocarditis is the major clinical manifestation of chronic Q fever. Although doxycycline along with hydroxychloroquine remains the mainstay of medical therapy for Q fever endocarditis, there are wide variations in the rapidity of the patient's decline of antibody levels during such therapy. We undertook a retrospective examination of whether there was any correlation between the ratio of serum concentration to MIC of doxycycline and response to treatment in patients with Q fever endocarditis. Included herein are 16 patients from whom Coxiella burnetii was isolated from cardiac valve materials. Serology and measurement of doxycycline and hydroxychloroquine serum levels were performed and recorded after 1 year of treatment. The MIC of doxycycline for C. burnetii isolates was determined using the shell vial assay in a real-time quantitative PCR assay. At the completion of a year-long therapy with doxycycline-hydroxychloroquine, all those that showed a low decline of antibody levels (n = 6) (i.e., <2-fold decrease in antibody titer to phase I C. burnetii antigen) had a ratio of serum doxycycline concentration to MIC between 0.5 and 1. In contrast, those having a ratio of > or =1 showed a rapid decline of phase I antibody levels (n = 9; P < 0.05). The only patient who died had a serum doxycycline-to-MIC ratio of <0.5, and the isolate of C. burnetii cultured from this patient was resistant to doxycycline (MIC = 8 microg/ml). The ratio of serum doxycycline concentration to MIC should be monitored during the course of therapy in patients with Q fever endocarditis.

Measurement of the antibiotic susceptibility of Coxiella burnetii using real time PCR

The objective of this study was to determine MICs of antibiotics for two reference strains of Coxiella burnetii using real time quantitative PCR. The method was very sensitive and specific and allowed the evaluation of the doubling time of Nine Mile and Q212 strains: 37 and 15 h, respectively. Dose response curves of antibiotics were used to determine MICs. Those of doxycycline, fluoroquinolone compounds and rifampicin were in the range 1-4 mg/l. Telithromycin was the most effective macrolide compound with MICs of 1-2 mg/l. The results confirmed previous reports on the accuracy of this new method for the determination of the antibiotic susceptibility of C. burnetii and could be used for the screening of new drugs.

Wolbachia pipientis growth kinetics and susceptibilities to 13 antibiotics determined by immunofluorescence staining and real-time PCR

Wolbachia spp. are strict intracellular bacteria that infect a wide range of arthropods and filarial nematodes. Filarial nematodes are important causes of human diseases. There is increasing evidence that Wolbachia spp. influence important functions in the biology of the hosts, specifically, infertility. Preliminary experiments with humans and animals have suggested that antibiotics with activity against Wolbachia may help to treat filariasis. In this study, we determined using a real-time quantitative PCR assay the growth kinetics of a strain of Wolbachia pipientis from a mosquito grown in Aa23 cells. The doubling time was estimated to be 14 h. We then determined the susceptibilities of this strain to 13 antibiotics by two methods: an immunofluorescent-antibody test and a real-time quantitative PCR assay. Both techniques gave similar results. Doxycycline and rifampin were the most effective compounds, with MICs of 0.125 and 0.06 to 0.125 micro g/ml, respectively. Fluoroquinolones were less effective, with MICs of 2 to 4 micro g/ml for ciprofloxacin, 2 micro g/ml for ofloxacin, and 1 micro g/ml for levofloxacin. beta-Lactams (penicillin G, amoxicillin, ceftriaxone) were not effective at concentrations up to 128 micro g/ml. The MIC of erythromycin was >32 micro g/ml, whereas that of telithromycin was 8 micro g/ml. Other antibiotic compounds were bacteriostatic only at high concentrations, including gentamicin, co-trimoxazole, and thiamphenicol. The real-time PCR assay was a convenient and reliable technique for determination of the antibiotic susceptibilities of WOLBACHIA: It may help in the future to simplify antibiotic susceptibility testing of strict intracellular pathogens.

Evaluation of Coxiella burnetii antibiotic susceptibilities by real-time PCR assay

Coxiella burnetii is an obligate intracellular bacterium. The inability to cultivate this organism on axenic medium has made calculation of infectious units challenging and prevents the use of conventional antibiotic susceptibility assays. A rapid and reliable real-time PCR assay was developed to quantify C. burnetii cells from J774.16 mouse macrophage cells and was applied to antibiotic susceptibility testing of C. burnetii Nine Mile, phase I. For calculation of bacterial replication, real-time PCR performed equally as well as immunofluorescent-antibody (IFA) assay when J774.16 cells were infected with 10-fold serial dilutions of C. burnetii and was significantly (P < 0.05) more repeatable than IFA when 2-fold dilutions were used. Newly infected murine macrophage-like J774.16 cells were treated with 8 microg of chloramphenicol per ml, 4 microg of tetracycline per ml, 4 microg of rifampin per ml, 4 microg of ampicillin per ml, or 1 microg of ciprofloxacin per ml. After 6 days of treatment, tetracycline, rifampin, and ampicillin significantly (P < 0.01) inhibited the replication of C. burnetii, while chloramphenicol and ciprofloxacin did not. In general, these results are consistent with those from prior reports on the efficacy of these antibiotics against C. burnetii Nine Mile, phase I, and indicate that a real-time PCR-based assay is an appropriate alternative to the present methodology for evaluation of the antibiotic susceptibilities of C. burnetii.

Q fever in children

Q fever is a zoonosis caused by Coxiella burnetii. Farm animals and pets are the main reservoirs of infection, and transmission to human beings is mainly accomplished through inhalation of contaminated aerosols. This illness is associated with a wide clinical spectrum, from asymptomatic or mildly symptomatic seroconversion to fatal disease. Q fever in children has been rarely reported. We reviewed published work on this topic. Seroepidemiological studies show that children are frequently exposed to C burnetii. However, children are less frequently symptomatic than adults following infection, and may have milder diseases. Using the standard diagnostic criteria, we identified 46 published paediatric cases only. Self-limited febrile illness and pneumonia were the most common manifestations of acute Q fever. Chronic disease manifested as endocarditis and osteomyelitis. A history of exposure to possible sources of infection with C burnetii in a child with a compatible infectious syndrome should prompt testing for Q fever. Studies are required to determine the spectrum of morbidity associated with Q fever during childhood.

In vitro susceptibility of Coxiella burnetii to linezolid in comparison with its susceptibilities to quinolones, doxycycline, and clarithromycin

The in vitro susceptibility to linezolid shown by nine Greek isolates of Coxiella burnetii derived from patients with acute Q fever was investigated. MICs of linezolid were compared with those of pefloxacin, ciprofloxacin, ofloxacin, trovafloxacin, doxycycline, and clarithromycin using the shell vial assay. MICs of linezolid and clarithromycin ranged from 2 to 4 microg/ml; those of doxycycline, trovafloxacin, and ofloxacin ranged from 1 to 2 microg/ml; those of pefloxacin ranged from 1 to 4 microg/ml; and those of ciprofloxacin ranged from 4 to 8 microg/ml. Linezolid was effective in controlling intracellular parasites in cultures of Vero cells infected by C. burnetii. No bactericidal activity by linezolid was obtained against C. burnetii at 8 microg/ml.

Bacteriostatic and bactericidal activities of moxifloxacin against Coxiella burnetii

The in vitro activity of moxifloxacin against Coxiella burnetii was compared to those of pefloxacin, ofloxacin, and doxycycline. MICs of moxifloxacin ranged from 0.5 to 1 microg/ml for the Nine Mile, Priscilla, and Q212 strains. Moxifloxacin was not bactericidal against C. burnetii at 4 microg/ml.

In vitro activities of telithromycin (HMR 3647) against Rickettsia rickettsii, Rickettsia conorii, Rickettsia africae, Rickettsia typhi, Rickettsia prowazekii, Coxiella burnetii, Bartonella henselae, Bartonella quintana, Bartonella bacilliformis, and Ehrlichia chaffeensis

In vitro activities of telithromycin compared to those of erythromycin against Rickettsia spp., Bartonella spp., Coxiella burnetii, and Ehrlichia chaffeensis were determined. Telithromycin was more active than erythromycin against Rickettsia, Bartonella, and Coxiella burnetii, with MICs of 0.5 microg/ml, 0.003 to 0.015 microg/ml, and 1 microg/ml, respectively, but was inactive against Ehrlichia chaffeensis.

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 vitro susceptibility of Coxiella burnetii to trovafloxacin in comparison with susceptibilities to pefloxacin, ciprofloxacin, ofloxacin, doxycycline, and clarithromycin

The antibiotic susceptibilities of eight Greek isolates of Coxiella burnetii to trovafloxacin were determined by the shell vial assay. MICs of trovafloxacin and ofloxacin ranged from 1 to 2 microg/ml, those of pefloxacin ranged from 1 to 4 microg/ml, those of ciprofloxacin ranged from 4 to 8 microg/ml, those of doxycycline ranged from 1 to 2 microg/ml, and those of clarithromycin ranged from 2 to 4 microg/ml. Trovafloxacin exhibited no activity against C. burnetii at 4 microg/ml.

Acute Q fever pneumonia: a review of 80 hospitalized patients

STUDY OBJECTIVES

To emphasize epidemiologic, clinical, or radiologic characteristics whose detection could lead to an early diagnosis and to enhance therapeutic efficacy.

PATIENTS

Eighty hospitalized patients from 1982 to 1996.

DESIGN

The diagnosis of Q fever infection was serologically confirmed in all the patients (phase II Coxiella burnetii antibody) using the complement fixation test and/or the indirect immunofluorescence antibody test.

RESULTS

Patients from rural and urban areas were noted in the same proportion; however, the usual epidemiologic factors such as contact with cats or farm animals were found in 40% of the patients. Mean age+/-SD was 49+/-20 years, and there was a higher sex ratio of male to female patients (1:3.44). We found a specific seasonal distribution since 80% of the cases occurred between February and May. Delay before referring to hospital was 8.2+/-7.8 days, while 69.3% of the patients received an antibiotic treatment that was mainly penicillin or cephalosporin. The dominant clinical features were dry cough and high fever, as the maximal temperature reached more then 40 degrees C in 58% of the patients. Digestive symptoms were rare. WBC count remained within normal range in 80% of the cases with a low proportion of lymphocytes in half of the patients, and the sedimentation rate was usually elevated (55+/-34 mm). Altered liver function consisted more frequently in an elevated level of alkaline phosphatase (70% of the cases) than transaminases, while hyponatremia was frequently mentioned (28.2% of the patients). We found radiologic evidence of unique lobar or segmental alveolar opacity involving more likely the lower lobes in 55 patients, and multiple or interstitial opacities in the others. Chest radiographs were considered normal in eight patients. The clinical response was favorable in all the patients with a reduction in fever 4.8+/-3.9 days after the start of treatment with the second antibiotic that included mainly erythromycin or quinolones, and chest radiographs returned to normal in 81% of the patients within the first month.

Q fever in the Greek island of Crete: detection, isolation, and molecular identification of eight strains of Coxiella burnetii from clinical samples

Over a period of 6 years (1989 to 1995), serum samples from 3,300 patients suspected to be infected by Coxiella burnetii were assayed for the presence of antibodies against antigen phase II of the microorganism by the indirect immunofluorescence antibody technique (IFAT). One hundred fifty-two cases were recorded, and blood samples from 17 patients were cultured for the isolation of the pathogen. By a centrifugation shell vial technique, eight strains were isolated from patients suffering from acute Q fever. The microorganism was detected in the cultures by IFAT, by Gimenez staining, and by the cytopathogenic effect on Vero and human embryonic lung (HEL) cells. PCR followed by restriction fragment length polymorphism analysis was used to confirm the diagnosis and identify the Coxiella burnetii strains within the cell cultures as well as to compare them with reference strains. In order to avoid time-consuming cultures, to achieve direct detection of Coxiella burnetii in clinical samples (blood, buffy coat, etc.), and to increase the specificity and sensitivity of the detection, nested PCR was performed. The first step of DNA extraction was performed with the QIAamp blood kit 250. For the second step of the PCR assays, the conditions of temperature and times of recycling were properly modified, and the microorganism was detected within 4 h. Our study demonstrates that Q fever is an endemic disease in Crete and that the diagnosis of Coxiella burnetii infection can be rapidly achieved by the detection of the microorganism in buffy coat samples by nested PCR. Although the presenting symptoms of the disease in this study differed from those in other studies, the Cretan strains do not differ genotypically from the reference strains (Nine Mile and Q212).

Treatment of atypical pneumonia with azithromycin: comparison of a 5-day and a 3-day course

The efficacy of a 5-day regimen consisting of 500 mg in a single dose on the first day followed by 250 mg once daily for 4 consecutive days was compared with that of a 3-day course of azithromycin given in single daily doses of 500 mg for treatment of atypical pneumonia. Adult patients hospitalized with atypical pneumonia in the years 1990 to 1993 were studied retrospectively. For each patient, the medical history, laboratory data, the results of serological tests, chest radiographs and treatment outcome were reviewed. Out of 148 patients with atypical pneumonia, 40 were treated with azithromycin for 5 days (Group 1) and 41 for 3 days (Group 2). The success rate in Group 1 was 80% (32 patients). Eight patients did not respond to treatment: 5 had significant complement fixing antibody titers to adenovirus and in 3 the etiology was unknown. The success rate in Group 2 was 88% (36 patients). Azithromycin was ineffective in all 3 patients with adenoviral pneumonia, in 1 patient with Q fever, and in 1 patient with no identified pathogen. Azithromycin is equally effective as treatment of atypical pneumonia in adult patients if given for 3 or 5 days at the same total dose.

Determination of Coxiella burnetii rpoB sequence and its use for phylogenetic analysis

The nucleotide sequence of the rpoB, encoding the beta-subunit of RNA polymerase of the obligate intracellular bacterium Coxiella burnetii, was determined using a polymerase chain reaction amplification and direct sequencing methodology. Comparison between C. burnetii and other eubacterial rpoB sequences indicated sequence similarity ranging from 53.6% to 67.6%. Coxiella burnetii rpoB consists of 4128 base pairs with a 45.3% GC content encoding 1375 amino acids with a calculated molecular mass of 153.67 kDa. Comparison of 512 bases of the rpoB variable region I, from eight C. burnetii strains isolated from various sources, revealed fewer than four base differences, although the distribution of these did not correlate with previously determined genotypic groupings with the species. Phylogenetic analysis of C. burnetii based on comparison of its rpoB sequence with sequences available for other bacteria is consistent with those previously derived from 16S rRNA gene sequence, and indicate that C. burnetii belongs to the gamma-group of Proteobacteria. Furthermore, phylogeny inferred from comparison of RpoB, or homologous sequences including Archae, Bacteria and Eukarya, concurred with these results.

Optimum treatment of intracellular infection

The intracellular location of some micro-organisms has been early recognised as a critical point to explain failure of antibiotic therapy to eradicate such pathogens from infected hosts. Most often parasites invade 'professional' phagocytic cells, including neutrophils, monocytes and macrophages, by resisting the intracellular bactericidal phagolysosomal pathway. Alternatively, they may invade 'non-professional' phagocytic cells (cells with fewer phagocytic and bactericidal abilities) such as endothelial cells, or even cells without lysosomes such as erythrocytes. The intracellular activity of an antibiotic depends on several factors including its ability to reach the eukaryotic cell membrane, its subcellular localisation as compared to that of the parasite, the possibility that the intracellular milieu may partially inactivate its activity, and the susceptibility of the intracellular form of the parasite. In vitro and animal models have been developed to investigate antibiotic activity against intracellular pathogens. However, it should be emphasised that only data obtained from patients give reliable information to define the optimum antibiotic regimen.

Sequence of quinolone resistance-determining region of gyrA gene for clinical isolates and for an in vitro-selected quinolone-resistant strain of Coxiella burnetii

We report the sequence of the quinolone resistance-determining region of the gyrA genes of either susceptible or low-level-resistant clinical isolates of Coxiella burnetii. The sequences of low-level (MICs, 4 micrograms/ml) and high-level (MICs, 8 and 16 micrograms/ml) resistant strains stepwise selected in vitro were also determined. The gene sequences of all of the clinical isolates and that of the in vitro-selected low-level-resistant strain were identical. Sequence analysis of the in vitro-selected high-level-resistant strain revealed a nucleotide mutation leading to an amino acid substitution of Gly in place of Glu at position 87 of the GyrA amino acid sequence. These results indicate that high-level resistance to ciprofloxacin is associated with a nucleotide mutation in gyrA, whereas low-level resistance to quinolones is not.

Coxiella burnetii blood cultures from acute and chronic Q-fever patients

Q fever, a worldwide zoonosis caused by Coxiella burnetii, may present as either an acute or a chronic disease. We correlated the results of 844 C. burnetii blood cultures with serological, clinical, and therapeutic data. C. burnetii was isolated from 17% of untreated patients with acute Q fever and from 53% of untreated patients with chronic Q fever. C. burnetii was not isolated from patients who were receiving antibiotics active against C. burnetii. For seven culture-positive patients with acute Q fever, serology was negative when C. burnetii was isolated. One patient with acute Q fever had a positive blood culture 25 days after the discontinuation of specific antibiotic therapy, and another had a positive blood culture after the resolution of symptoms. In one case of chronic Q fever, a positive blood culture resulted from noncompliance with treatment. The culture method described in this report is suitable for all laboratories with cell culture facilities. Our findings suggest that blood samples must be collected prior to the initiation of an antibiotic regimen if C. burnetii is to be successfully isolated.

Intracellular concentrations of antibacterial agents and related clinical implications

Intracellular penetration, accumulation and disposition of antibacterial agents is crucial for effective treatment of infections caused by intracellular bacteria. Intracellular concentrations and locations of both antibacterials and bacteria remain poorly understood and further research is needed to establish the importance of these concepts. For example, concepts that have been shown to be important outcome predictors when applied to concentrations of antibacterial agents in the serum include: (i) the effect of the peak antibacterial serum concentration to minimum concentration inhibitory to 90% of organisms (MIC90) for bacteria; (ii) the effect of length of time the serum antibacterial concentration remains above the MIC90 curve; or (iii) the area under the MIC90 curve, but above the serum antibacterial concentration curve. Further research should determine whether or not these concepts have important applications in an intracellular environment. Intracellular pathogens have been increasingly contributing to respiratory infections in the community. Therefore, on the basis of intracellular activity against bacteria causing respiratory infections, macrolides are favoured as the most broad spectrum class of oral antibacterial agents available for the treatment of patients with community-acquired respiratory infections.

In vitro susceptibilities of spotted fever group rickettsiae and Coxiella burnetti to clarithromycin

The in vitro bacteriostatic activity of clarithromycin, a new macrolide derivative, against Rickettsia rickettsii, Rickettsia conorii, and "Rickettsia israeli" was determined by the plaque assay and the dye uptake assay. Both bacteriostatic and bactericidal activities of clarithromycin against the Nine Mile, Q212, Priscilla, and ME9 strains of Coxiella burnetti were evaluated by using three cell culture systems. Clarithromycin showed improved antibacterial activity compared with that of erythromycin. A bacteriostatic activity was obtained at concentrations below the reported maximum concentration of clarithromycin in human serum (about 4 micrograms/ml) for all tested rickettsiae. MICs ranged from 1 to 2 micrograms/ml for the three Rickettsia species and from 1 to 4 micrograms/ml for the C. burnetti strains. No bactericidal activity against C. burnetti was obtained when clarithromycin was used at 4 micrograms/ml.