Background. Blood culture-negative endocarditis (BCNE) may account for up to 31% of all cases of endocarditis. Methods. We used a prospective, multimodal strategy incorporating serological, ...molecular, and histopathological assays to investigate specimens from 819 patients suspected of having BCNE. Results. Diagnosis of endocarditis was first ruled out for 60 patients. Among 759 patients with BCNE, a causative microorganism was identified in 62.7%, and a noninfective etiology in 2.5%. Blood was the most useful specimen, providing a diagnosis for 47.7% of patients by serological analysis (mainly Q fever and Bartonella infections). Broad-range polymerase chain reaction (PCR) of blood and Bartonella-specific Western blot methods diagnosed 7 additional cases. PCR of valvular biopsies identified 109 more etiologies, mostly streptococci, Tropheryma whipplei, Bartonella species, and fungi. Primer extension enrichment reaction and autoimmunohistochemistry identified a microorganism in 5 additional patients. No virus or Chlamydia species were detected. A noninfective cause of endocarditis, particularly neoplasic or autoimmune disease, was determined by histological analysis or by searching for antinuclear antibodies in 19 (2.5%) of the patients. Our diagnostic strategy proved useful and sensitive for BCNE workup. Conclusions. We highlight the major role of zoonotic agents and the underestimated role of noninfective diseases in BCNE. We propose serological analysis for Coxiella burnetii and Bartonella species, detection of antinuclear antibodies and rheumatoid factor as first-line tests, followed by specific PCR assays for T. whipplei, Bartonella species, and fungi in blood. Broad-spectrum 16S and 18S ribosomal RNA PCR may be performed on valvular biopsies, when available.
Background.Campylobacter bacteremia is uncommon. The influence of underlying conditions and of the impact of antibiotics on infection outcome are not known. Methods.From January 2000 through December ...2004, 183 episodes of Campylobacter bacteremia were identified in 23 hospitals in the Paris, France, area. The medical records were reviewed. Characteristics of bacteremia due to Campylobacter fetus and to other Campylobacter species were compared. Logistic regression analysis was performed to identify risk factors for fatal outcome within 30 days. Results.Most affected patients were elderly or immunocompromised. C. fetus was the most commonly identified species (in 53% of patients). The main underlying conditions were liver disease (39%) and cancer (38%). The main clinical manifestations were diarrhea (33%) and skin infection (16%). Twenty-seven patients (15%) died within 30 days. Compared with patients with bacteremia due to other Campylobacter species, patients with C. fetus bacteremia were older (mean age, 69.5 years vs. 55.6 years; P<.001) and were more likely to have cellulitis (19% vs. 7%; P=.03), endovascular infection (13% vs. 1%; P=.007), or infection associated with a medical device (7% vs. 0%; P=.02). Independent risk factors for death were cancer (odds ratio OR, 5.1; 95% confidence interval CI, 1.2–20.8) and asymptomatic infection (OR, 6.7; 95% CI, 1.5–29.4) for C. fetus bacteremia, the absence of prescription of appropriate antibiotics (OR, 12.2; 95% CI, 0.9–157.5), and prescription of third-generation cephalosporins (OR, 10.2; 95% CI, 1.9–53.7) for bacteremia caused by other species. Conclusions.Campylobacter bacteremia occurs mainly in immunocompromised patients. Clinical features and risk factors of death differ by infection species.
There is a renewed interest for β‐lactams for treating infections due to Mycobacterium tuberculosis and M. abscessus because their β‐lactamases are inhibited by classical (clavulanate) or new ...generation (avibactam) inhibitors, respectively. Here, access to an azido derivative of the diazabicyclooctane (DBO) scaffold of avibactam for functionalization by the Huisgen–Sharpless cycloaddition reaction is reported. The amoxicillin–DBO combinations were active, indicating that the triazole ring is compatible with drug penetration (minimal inhibitory concentration of 16 μg mL−1 for both species). Mechanistically, β‐lactamase inhibition was not sufficient to account for the potentiation of amoxicillin by DBOs. Thus, the latter compounds were investigated as inhibitors of l,d‐transpeptidases (Ldts), which are the main peptidoglycan polymerases in mycobacteria. The DBOs acted as slow‐binding inhibitors of Ldts by S‐carbamoylation indicating that optimization of DBOs for Ldt inhibition is an attractive strategy to obtain drugs selectively active on mycobacteria.
DBO for TB! A synthetic route to functionalized diazabicyclooctanes (DBOs) was developed based on incorporation of an azido group for CuI‐catalyzed Huisgen–Sharpless cycloaddition. DBOs inhibited the l,d‐transpeptidases involved in peptidoglycan polymerization in addition to the expected activity on β‐lactamases. Optimization of DBOs for inhibition of peptidoglycan polymerases is an attractive strategy to obtain drugs selectively active on mycobacteria.
Acquisition of resistance to the two classes of antibiotics therapeutically used against Gram-positive bacteria, the glycopeptides and the β-lactams, has revealed an unexpected flexibility in the ...peptidoglycan assembly pathway. Glycopeptides select for diversification of the fifth position of stem pentapeptides because replacement of d-Ala by d-lactate or d-Ser at this position prevents binding of the drugs to peptidoglycan precursors. The substitution is generally well tolerated by the classical d,d-transpeptidases belonging to the penicillin-binding protein family, except by low-affinity enzymes. Total elimination of the fifth residue by a d,d-carboxypeptidase requires a novel cross-linking enzyme able to process the resulting tetrapeptide stems. This enzyme, an l,d-transpeptidase, confers cross-resistance to β-lactams and glycopeptides. Diversification of the side chain of the precursors, presumably in response to the selective pressure of peptidoglycan endopeptidases, is controlled by aminoacyl transferases of the Fem family that redirect specific aminoacyl-tRNAs from translation to peptidoglycan synthesis. Diversification of the side chains has been accompanied by a parallel divergent evolution of the substrate specificity of the l,d-transpeptidases, in contrast to the d,d-transpeptidases, which display an unexpected broad specificity. This review focuses on the role of antibiotics in selecting or counter-selecting diversification of the structure of peptidoglycan precursors and their mode of polymerization.
The peptidoglycan layer is a vital component of the bacterial cell wall. The existing paradigm describes the peptidoglycan network as a static structure that is cross-linked predominantly by 4→3 ...transpeptide linkages. However, the nonclassical 3→3 linkages predominate the transpeptide networking of the peptidoglycan layer of nonreplicating Mycobacterium tuberculosis. The molecular basis of these linkages and their role in the physiology of the peptidoglycan layer, virulence and susceptibility of M. tuberculosis to drugs remain undefined. Here we identify MT2594 as an L,D-transpeptidase that generates 3→3 linkages in M. tuberculosis. We show that the loss of this protein leads to altered colony morphology, loss of virulence and increased susceptibility to amoxicillin-clavulanate during the chronic phase of infection. This suggests that 3→3 cross-linking is vital to the physiology of the peptidoglycan layer. Although a functional homolog exists, expression of ldtMt2 is dominant throughout the growth phases of M. tuberculosis. 4→3 transpeptide linkages are targeted by one of the most widely used classes of antibacterial drugs in human clinical use today, β-lactams. Recently, meropenem-clavulanate was shown to be effective against drug-resistant M. tuberculosis. Our study suggests that a combination of L,D-transpeptidase and β-lactamase inhibitors could effectively target persisting bacilli during the chronic phase of tuberculosis.
Bacteriophages are a promising therapeutic strategy among cystic fibrosis and lung-transplanted patients, considering the high frequency of colonization/infection caused by pandrug-resistant ...bacteria. However, little clinical data are available regarding the use of phages for infections with
. A 12-year-old lung-transplanted cystic fibrosis patient received two rounds of phage therapy because of persistent lung infection with pandrug-resistant
. Clinical tolerance was perfect, but initial bronchoalveolar lavage (BAL) still grew
. The patient's respiratory condition slowly improved and oxygen therapy was stopped. Low-grade airway colonization by
persisted for months before samples turned negative. No re-colonisation occurred more than two years after phage therapy was performed and imipenem treatment was stopped. Whole genome sequencing indicated that the eight
isolates, collected during phage therapy, belonged to four delineated strains, whereby one had a stop mutation in a gene for a phage receptor. The dynamics of lung colonisation were documented by means of strain-specific qPCRs on different BALs. We report the first case of phage therapy for
lung infection in a lung-transplanted patient. The dynamics of airway colonization was more complex than deduced from bacterial culture, involving phage susceptible as well as phage resistant strains.
infections are difficult to treat because of their resistance to many antibiotics.
, tedizolid combined with imipenem displayed a moderate synergistic effect (fractional inhibitory concentration ...index, 0.41) but no bactericidal activity. Intracellularly, tedizolid 2 μg/ml (half of the MIC), corresponding to the peak serum concentration, increased the efficacy of imipenem at 8 and 32 μg/ml. Addition of avibactam and rifabutin, alone or in combination, improved the activity of the imipenem-tedizolid combination.
Two β-lactams, cefoxitin and imipenem, are part of the reference treatment for pulmonary infections with Mycobacterium abscessus. M. abscessus has recently been shown to produce a broad-spectrum ...β-lactamase, BlaMab, indicating that the combination of β-lactams with a BlaMab inhibitor may improve treatment efficacy. The objectives of this study were to evaluate the impact of BlaMab production on the efficacy of β-lactams in vitro and to assess the benefit of BlaMab inhibition on the activity of β-lactams intracellularly and in an animal model.
We analysed the mechanism and kinetics of BlaMab inactivation by avibactam, a non-β-lactam β-lactamase inhibitor currently in Phase III of development, in combination with ceftazidime for the treatment of serious infections due to Gram-negative bacteria. We then deleted the gene encoding BlaMab to assess the extent of BlaMab inhibition by avibactam based on a comparison of the impact of chemical and genetic inactivation. Finally, the efficacy of amoxicillin in combination with avibactam was evaluated in cultured human macrophages and in a zebrafish model of M. abscessus infection.
We showed that avibactam efficiently inactivated BlaMab via the reversible formation of a covalent adduct. An inhibition of BlaMab by avibactam was observed in both infected macrophages and zebrafish.
Our data identify avibactam as the first efficient inhibitor of BlaMab and strongly suggest that β-lactamase inhibition should be evaluated to provide improved therapeutic options for M. abscessus infections.
To comparatively evaluate the performance of the rapid antimicrobial susceptibility testing (AST) system QMAC-dRAST V2.0 and of standard disk diffusion in agar, AST was performed directly from 100 ...positive blood culture bottles with Gram-negative bacilli. AST results provided by QMAC-dRAST showed 92.9% agreement with disk diffusion method results. Discrepancies observed between results obtained with QMAC-dRAST and disk diffusion method conducted to 10 very major errors (0.8%, S with QMAC-dRAST vs R with disk diffusion method), 40 major errors (3.2%, R vs S, respectively), 15 minor errors (1.2%, S vs I or I vs R, respectively) and 23 very minors errors (1.8%, I vs S or R vs I, respectively). For very major and major errors, in only 36% of the cases did the repeat QMAC-dRAST confirm the initial result, whereas a repeat AST using disk diffusion method confirmed the initial result in 92% of cases. AST results obtained using microdilution in liquid medium confirmed those obtained with QMAC-dRAST and disk diffusion method in 4% and 89%, respectively. Repeatability and reproducibility tests performed on QMAC-dRAST using reference strains showed 94% to 100% of R/S/I categorical agreement.
•Time necessary to obtain AST result using the QMAC-dRAST V2.0 is 7 h.•QMAC-dRAST and disk diffusion method results show 92.9% agreement.•Repeatability using reference strains was 94–100% of R/S/I categorical agreement.•Easy-to-use system but the prototype tested would benefit from being optimized.
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