In vitro activities of ceftriaxone and fusidic acid against 13 isolates of Coxiella burnetii, determined using the shell vial assay

Challenging case of chronic Q fever endocarditis: usefulness of 18F-FDG PET/CT in the diagnosis and follow-up

Diagnosis of infective endocarditis can be challenging for clinicians, especially when involving prosthetic valves. Recent data suggest that 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) could be a useful diagnostic tool in this setting. Here, we report a case of a patient with an aortic biological prosthesis who presented with a history of fever and fatigue. Echocardiograms were negative for vegetations. The 18F-FDG PET/CT revealed an infective process of the valve and serological tests were positive for chronic Coxiella burnetii infection. Specific treatment for chronic Q fever endocarditis was, therefore, started and the response was monitored using 18F-FDG PET/CT. This case highlights the challenges and pitfalls clinicians face when confronted with prosthetic valve endocarditis and the use of 18F-FDG PET/CT for diagnosis and follow-up.

Comparison of in vivo pathogenicity of four Candida auris clades in a neutropenic bloodstream infection murine model

Candida auris is an emerging worldwide concern, but comparative data about the virulence of different C. auris lineages in mammalian hosts is lacking. Different isolates of the four prevalent C. auris clades (South Asian n = 5, East Asian n = 4, South African n = 5, and South American n = 5) were compared to assess their virulence in a neutropenic murine bloodstream infection model with C. albicans as reference. C. auris, regardless of clade, proved to be less virulent than C. albicans. Highest overall mortality at day 21 was observed for the South American clade (96%), followed by the South Asian (80%), South African (45%) and East Asian (44%) clades. Fungal burden results showed close correlation with lethality. Histopathological examination revealed large aggregates of blastoconidia and budding yeast cells in the hearts, kidneys and livers but not in the spleens. The myocardium of apparently healthy sacrificed mice as well as of mice found moribund showed contraction band necrosis in case of all lineages. Regardless of clade, the heart and kidneys were the most heavily affected organs. Isolates of the same clade showed differences in virulence in mice, but a markedly higher virulence of the South American clade was clearly demonstrated.

Human metallo-β-lactamase enzymes degrade penicillin

Nonribosomal peptides are assemblages, including antibiotics, of canonical amino acids and other molecules. β-lactam antibiotics act on bacterial cell walls and can be cleaved by β-lactamases. β-lactamase activity in humans has been neglected, even though eighteen enzymes have already been annotated such in human genome. Their hydrolysis activities on antibiotics have not been previously investigated. Here, we report that human cells were able to digest penicillin and this activity was inhibited by β-lactamase inhibitor, i.e. sulbactam. Penicillin degradation in human cells was microbiologically demonstrated on Pneumococcus. We expressed a MBLAC2 human β-lactamase, known as an exosome biogenesis enzyme. It cleaved penicillin and was inhibited by sulbactam. Finally, β-lactamases are widely distributed, archaic, and have wide spectrum, including digesting anticancer and β-lactams, that can be then used as nutriments. The evidence of the other MBLAC2 role as a bona fide β-lactamase allows for reassessment of β-lactams and β-lactamases role in humans.

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.

[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.

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

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.

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.

Fusidic acid in vitro activity

Fusidic acid is a narrow spectrum agent that acts to inhibit protein synthesis by inhibition of elongation factor G at the level of the ribosome. Because of high protein binding susceptibility testing in vitro is affected by the presence of blood or serum. In addition, there is a modest inoculum effect in vitro. A breakpoint of 1 or 2 mg/l is most widely used for defining resistance to systemic treatment with fusidic acid. Fusidic acid activity is principally directed at staphylococci, both Staphylococcus aureus and coagulate-negative species which are highly susceptible. It is also active against Gram-positive anaerobic activity, and shows in vitro activity against Neisseria spp., Bordetella pertussis and Moraxella catarrhalis. It has no activity against other aerobic Gram-negative species. Modest activity (MICs just above breakpoint values) is seen with Streptococcus and Enterococcus spp. as well as Gram-negative anaerobic bacteria. Fusidic acid is defined as bacteriostatic. For staphylococci MBC values are generally 8--32-fold that of the MIC. Interaction studies with other antibiotics give varying results depending on methodology. However, interaction with beta-lactams is generally indifferent, as it is with rifampicin, while aminoglycosides and macrolides appear to be synergistic and fluoroquinolones antagonistic. Fusidic acid appears to inhibit the function of neutrophils and T-lymphocytes at clinically achieved concentrations.

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.