Impact of oleic acid (cis-9-octadecenoic acid) on bacterial viability and biofilm production in Staphylococcus aureus

Staphylococcus aureus is responsible for a broad variety of chronic infections. Most S. aureus clinical isolates show the capacity to adhere to abiotic surfaces and to develop biofilms. Because S. aureus growing in a biofilm is highly refractory to treatment, inhibition of biofilm formation represents a major therapeutic objective. We evaluated the effects of oleic acid on primary adhesion and biofilm production in eight genotypically different S. aureus strains as well as in the biofilm-negative Staphylococcus carnosus strain TM300. Oleic acid inhibited primary adhesion but increased biofilm production in every S. aureus strain tested. Staphylococcus aureus strain UAMS-1 was then selected as a model organism for studying the mechanisms triggered by oleic acid on the formation of a biofilm in vitro. Oleic acid inhibited the primary adhesion of UAMS-1 dose dependently with an IC50 around 0.016%. The adherent bacterial population decreased proportionally with increasing concentrations of oleic acid whereas an opposite effect was observed on the planktonic population. Overall, the total bacterial counts remained stable. Macroscopic detachments and clumps were visible from the adherent bacterial population. In the presence of oleic acid, the expression of sigB, a gene potentially involved in bacterial survival through an effect on fatty acid composition, was not induced. Our results suggest a natural protective effect of oleic acid against primary adhesio

Risk factors for noma disease: a 6-year, prospective, matched case-control study in Niger

Background Noma is a poorly studied disease that leads to severe facial tissue destruction in children in developing countries, but the cause remains unknown. We aimed to identify the epidemiological and microbiological risk factors associated with noma disease. Methods We did a prospective, matched, case-control study in Niger between Aug 1, 2001, and Oct 31, 2006, in children younger than 12 years to assess risk factors for acute noma. All acute noma cases were included and four controls for each case were matched by age and home village. Epidemiological and clinical data were obtained at study inclusion. We undertook matched-paired analyses with conditional logistic regression models. Findings We included 82 cases and 327 controls. Independent risk factors associated with noma were: severe stunting (odds ratio [OR] 4·87, 95% CI 2·35–10·09) or wasting (2·45, 1·25–4·83); a high number of previous pregnancies in the mother (1·16, 1·04–1·31); the presence of respiratory disease, diarrhoea, or fever in the past 3 months (2·70, 1·35–5·40); and the absence of chickens at home (1·90, 0·93–3·88). After inclusion of microbiological data, a reduced proportion of Fusobacterium (4·63, 1·61–13·35), Capnocytophaga (3·69, 1·48–9·17), Neisseria (3·24, 1·10–9·55), and Spirochaeta in the mouth (7·77, 2·12–28·42), and an increased proportion of Prevotella (2·53, 1·07–5·98), were associated with noma. We identifi ed no specifi c single bacterial or viral pathogen in cases. Interpretation Noma is associated with indicators of severe poverty and altered oral microbiota. The predominance of specifi c bacterial commensals is indicative of a modifi cation of the oral microbiota associated with reduced bacterial diversity.Funding Gertrude Hirzel Foundation

Methicillin-Resistant Staphylococcus aureus, Geneva, Switzerland, 1993–2005

Molecular characterization of methicillin-resistant Staphylococcus aureus (MRSA) strains different from those of an endemic healthcare-associated clone was conducted over 13 years in Geneva, Switzerland. We demonstrated strain diversity, including clones rarely found in Europe. Local epidemiology of community-associated MRSA is diverse and is evolving by importation and transmission of new strains

Community-associated Methicillin-resistant Staphylococcus aureus, Switzerland

Two case-control studies evaluated the prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) carriage at hospital admission and characteristics of patients with CA-MRSA. Among 14,253 patients, CA-MRSA prevalence was 0.9/1,000 admissions. Although 5 CA-MRSA isolates contained Panton-Valentine leukocidin, only 1 patient had a previous skin infection. No easily modifiable risk factor for CA-MRSA was identified

Exploring glycopeptide-resistance in Staphylococcus aureus: a combined proteomics and transcriptomics approach for the identification of resistance-related markers

BACKGROUND: To unravel molecular targets involved in glycopeptide resistance, three isogenic strains of Staphylococcus aureus with different susceptibility levels to vancomycin or teicoplanin were subjected to whole-genome microarray-based transcription and quantitative proteomic profiling. Quantitative proteomics performed on membrane extracts showed exquisite inter-experimental reproducibility permitting the identification and relative quantification of >30% of the predicted S. aureus proteome. RESULTS: In the absence of antibiotic selection pressure, comparison of stable resistant and susceptible strains revealed 94 differentially expressed genes and 178 proteins. As expected, only partial correlation was obtained between transcriptomic and proteomic results during stationary-phase. Application of massively parallel methods identified one third of the complete proteome, a majority of which was only predicted based on genome sequencing, but never identified to date. Several over-expressed genes represent previously reported targets, while series of genes and proteins possibly involved in the glycopeptide resistance mechanism were discovered here, including regulators, global regulator attenuator, hyper-mutability factor or hypothetical proteins. Gene expression of these markers was confirmed in a collection of genetically unrelated strains showing altered susceptibility to glycopeptides. CONCLUSION: Our proteome and transcriptome analyses have been performed during stationary-phase of growth on isogenic strains showing susceptibility or intermediate level of resistance against glycopeptides. Altered susceptibility had emerged spontaneously after infection with a sensitive parental strain, thus not selected in vitro. This combined analysis allows the identification of hundreds of proteins considered, so far as hypothetical protein. In addition, this study provides not only a global picture of transcription and expression adaptations during a complex antibiotic resistance mechanism but also unravels potential drug targets or markers that are constitutively expressed by resistant strains regardless of their genetic background, amenable to be used as diagnostic targets

Innovative DNA microarray design for bacterial flora composition evaluation

During the past decade, the advent of new molecular techniques has led to enormous progress in biology, notably with the development of DNA microarray technology. This technology allows monitoring simultaneously the expression of thousands of genes from a given organism. DNA microarrays have been used in a variety of applications, including the characterization of bacteria in biological samples. In this thesis, two distinct DNA microarray approaches for the characterization of bacterial flora are introduced. The first approach, termed phylogenetic microarrays, consists in a probe set recognizing specific sequence signatures for each node of the bacterial phylogenetic tree. This strategy, based on sequence information, allows extending the scope of microarrays to the whole bacterial kingdom and detecting both known and unknown microorganisms in biological samples. Moreover, phylogenetic microarrays permit detection of a broader bacterial diversity compared to the classical cloning-sequencing approach. The second strategy consists in a low-density 16S rRNA gene microarray specifically designed to monitor bacterial species found in the gingival flora of African children suffering from noma, a devastating disease of unknown etiology. In an attempt to identify the causative agent(s) of noma, these two methodologies were applied for the characterization of the gingival flora of children suffering from the disease. Observations made during this study allowed exonerating Fusobacterium necrophorum, considered by some experts as the causative agent of noma. Moreover, various oral pathogens were recovered in higher abundance in noma lesions, notably Atopobium spp., Peptostreptococcus spp., Prevotella intermedia, Streptococcus pyogenes and Streptococcus anginosus. In addition, noma lesions exhibited a lower bacterial diversity compared to acute necrotizing gingivitis (ANG), thus supporting a previous hypothesis that ANG might precede acute noma. The accomplished work, while giving better insights on the bacteriology of noma, demonstrates the power of the two developed approaches to explore and systematically characterize complex microbial communities

Les systèmes d'information en appui à la connaissance et la diffusion des systèmes de culture économes en pesticides : l'exemple du système d'information Agrosyst du réseau de fermes et d'expérimentations du plan Ecophyto

National audienc

Temps qui passe, temps qu'il fait

Responsables du numéro et coordination éditoriale : Caroline Norrant et Antoine Le Blan