Résistance aux antibiotiques par mécanisme d'efflux chez Achromobacter xylosoxidans

Achromobacter xylosoxidans est un bacille à Gram négatif non fermentaire pathogène opportuniste. Il est de plus en plus fréquemment isolé chez les patients atteints de mucoviscidose, colonisant leur arbre bronchique et pouvant être responsable d une dégradation de la fonction respiratoire. Il s agit d une espèce bactérienne naturellement résistante à de nombreux antibiotiques : aux céphalosporines (hors ceftazidime), à l aztréonam et aux aminosides. Les résistances acquises sont fréquentes, en particulier dans les souches isolées d expectorations de patients atteints de mucoviscidose. Ces résistances acquises concernent des molécules antibiotiques très utilisées pour le traitement des exacerbations respiratoires de la maladie, ce qui conduit parfois à de véritables impasses thérapeutiques. Au début de notre travail, seuls quelques mécanismes de résistance acquise aux b-lactamines avaient été décrits, mais aucun mécanisme impliqué dans la multi-résistance naturelle d A. xylosoxidans.La résistance aux antibiotiques par efflux actif de type Resistance-Nodulation-cell Division (RND) est très répandue chez les bacilles à Gram négatif non fermentaires. Nous avons identifié dans le génome d A. xylosoxidans trois opérons pouvant coder pour des systèmes d efflux RND. Par une technique d inactivation génique nous avons montré que les trois systèmes d efflux (AxyABM, AxyXY-OprZ et AxyCDJ) pouvaient exporter des antibiotiques. Deux d entre eux participent à l antibio-résistance naturelle d A. xylosoxidans : AxyABM (résistance à l aztréonam et à plusieurs céphalosporines) et AxyXY-OprZ (résistance aux aminosides)Achromobacter xylosoxidans is a nonfermentative Gram-negative bacillus considered to be an opportunistic agent. It is an emerging pathogen in cystic fibrosis (CF), increasingly recovered from the respiratory tract of CF patients. It can cause inflammation and therefore might be involved in the decline of the lung function.This species is innately resistant to many antibiotics, including cephalosporins (except ceftazidime), aztreonam, and aminoglycosides. Moreover the isolates recovered from CF patient sputum are often resistant to major antimicrobial components usually prescribed to treat pulmonary infections. There was very little known about acquired resistance and nothing about innate resistance mechanisms when we started this work.Antibiotic resistance mediated by Resistance-Nodulation-cell Division (RND)-type efflux pumps is widespread among nonfermentative Gram-negative bacilli. We have characterized three putative RND operons in A. xylosoxidans genome. By using a gene inactivation technique we have demonstrated that these operons encode efflux systems (AxyABM, AxyXY-OprZ and AxyCDJ) able to export antibiotics. Two of them are strongly involved in A. xylosoxidans innate antibiotic resistance: AxyABM (resistance to aztreonam and various cephalosporins) and AxyXY-OprZ (aminoglycoside resistance).DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Occurrence of CTX-M Producing Escherichia coli in Soils, Cattle, and Farm Environment in France (Burgundy Region)

CTX-M [a major type of extended-spectrum beta-lactamase (ESBL)] producing Escherichia coli are increasingly involved in human infections worldwide. The aim of this study was to investigate potential reservoirs for such strains: soils, cattle, and farm environment. The prevalence of blaCTX-M genes was determined directly from soil DNA extracts obtained from 120 sites in Burgundy (France) using real-time PCR. blaCTX-M targets were found in 20% of the DNA extracts tested. Samples of cattle feces (n = 271) were collected from 182 farms in Burgundy. Thirteen ESBL-producing isolates were obtained from 12 farms and further characterized for the presence of bla genes. Of the 13 strains, five and eight strains carried blaTEM-71 genes and blaCTX-M-1 genes respectively. Ten strains of CTX-M-1 producing E. coli were isolated from cultivated and pasture soils as well as from composted manure within two of these farms. The genotypic analysis revealed that environmental and animal strains were clonally related. Our study confirms the occurrence of CTX-M producing E. coli in cattle and reports for the first time the occurrence of such strains in cultivated soils. The environmental competence of such strains has to be determined and might explain their long term survival since CTX-M isolates were recovered from a soil that was last amended with manure 1 year before sampling

VEB-1 in Achromobacter xylosoxidans from Cystic Fibrosis Patient, France

Multidrug-resistant Achromobacter xylosoxidans was recovered from the sputum of a patient with cystic fibrosis. The VEB-1 extended-spectrum β-lactamase was detected on a class 1 integron. This first report of a VEB-1–producing isolate in this population requires further investigation to determine its distribution

Staphylococcus aureus infective endocarditis versus bacteremia strains: Subtle genetic differences at stake

AbstractInfective endocarditis (IE)(1) is a severe condition complicating 10–25% of Staphylococcus aureus bacteremia. Although host-related IE risk factors have been identified, the involvement of bacterial features in IE complication is still unclear. We characterized strictly defined IE and bacteremia isolates and searched for discriminant features. S. aureus isolates causing community-acquired, definite native-valve IE (n=72) and bacteremia (n=54) were collected prospectively as part of a French multicenter cohort. Phenotypic traits previously reported or hypothesized to be involved in staphylococcal IE pathogenesis were tested. In parallel, the genotypic profiles of all isolates, obtained by microarray, were analyzed by discriminant analysis of principal components (DAPC)(2). No significant difference was observed between IE and bacteremia strains, regarding either phenotypic or genotypic univariate analyses. However, the multivariate statistical tool DAPC, applied on microarray data, segregated IE and bacteremia isolates: IE isolates were correctly reassigned as such in 80.6% of the cases (C-statistic 0.83, P<0.001). The performance of this model was confirmed with an independent French collection IE and bacteremia isolates (78.8% reassignment, C-statistic 0.65, P<0.01). Finally, a simple linear discriminant function based on a subset of 8 genetic markers retained valuable performance both in study collection (86.1%, P<0.001) and in the independent validation collection (81.8%, P<0.01). We here show that community-acquired IE and bacteremia S. aureus isolates are genetically distinct based on subtle combinations of genetic markers. This finding provides the proof of concept that bacterial characteristics may contribute to the occurrence of IE in patients with S. aureus bacteremia

Etude de la résistance à la lévofloxacine d'une souche clinique de streptococcus mitis

DIJON-BU Médecine Pharmacie (212312103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Etude de la résistance à la lévofloxacine d'une souche clinique de streptococcus mitis

DIJON-BU Médecine Pharmacie (212312103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Mise au point de techniques de typage moléculaire de souches de salmonella Virchow à la suite d'une infection fatale chez un nourrisson (DES de Biologie médicale)

DIJON-BU Médecine Pharmacie (212312103) / SudocSudocFranceF

Recherche et caractérisation d'intégrons de classe 1 au sein de Pseudomonas aeruginosa

DIJON-BU Médecine Pharmacie (212312103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Caractérisation phénotypique et moléculaire de souches de Pseudomonas aeruginosa productrices de la métallo b-lactamase IMP-19 isolées chez des patients du service d'hématologie clinique du CHU de Dijon et dans l'environnement humide

DIJON-BU Médecine Pharmacie (212312103) / SudocSudocFranceF