Evoked response activity eigenmode analysis in a convoluted cortex via neural field theory.

Neural field theory of the corticothalamic system is used to explore evoked response potentials (ERPs) caused by spatially localized impulse stimuli on the convoluted cortex and on a spherical cortex. Eigenfunctions are calculated analytically on the spherical cortex and numerically on the convoluted cortex via eigenfunction expansions. Eigenmodes on a convoluted cortex are similar to those of the spherical cortex, and a few such modes are found to be sufficient to reproduce the main ERP features. It is found that the ERP peak is stronger in spherical cortex than convoluted cortex, but in both cases the peak decreases monotonically with increasing distance from the stimulus point. In the convoluted case, cortical folding causes ERPs to differ between locations at the same distance from the stimulus point and spherical symmetries are only approximately preserved.

Neural field theory of perceptual echo and implications for estimating brain connectivity.

Neural field theory is used to predict and analyze the phenomenon of perceptual echo in which random input stimuli at one location are correlated with electroencephalographic responses at other locations. It is shown that this echo correlation (EC) yields an estimate of the transfer function from the stimulated point to other locations. Modal analysis then explains the observed spatiotemporal structure of visually driven EC and the dominance of the alpha frequency; two eigenmodes of similar amplitude dominate the response, leading to temporal beating and a line of low correlation that runs from the crown of the head toward the ears. These effects result from mode splitting and symmetry breaking caused by interhemispheric coupling and cortical folding. It is shown how eigenmodes obtained from functional magnetic resonance imaging experiments can be combined with temporal dynamics from EC or other evoked responses to estimate the spatiotemporal transfer function between any two points and hence their effective connectivity.

Predictors of disease-free survival in colorectal cancer with microsatellite instability: An AGEO multicentre study.

BACKGROUND: A microsatellite instability (MSI) phenotype is found in about 12% of colorectal cancers (CRCs) and is associated with a low recurrence rate after curative surgery. Several studies have identified clinical and pathological factors predictive of recurrence in resected CRC, but not in the MSI subgroup. PATIENTS AND METHODS: This multicentre retrospective study included patients with stage I, II or III MSI CRCs. Disease-free survival (DFS) was calculated with the Kaplan-Meier method. Factors associated with DFS were identified in univariate and multivariate Cox analyses. RESULTS: We studied 521 patients with MSI CRC. Respectively 11%, 51% and 38% of patients were at stage I, II and III. Mean age was 68.7years and 36% of the patients received adjuvant chemotherapy. Median follow-up was 32.8months. The disease recurrence rates were 6% and 21% in stage II and III patients, respectively. The 3-year DFS rate was 77%. In univariate analysis, age, bowel obstruction, lymph node invasion, stage T4, vascular emboli, lymphatic invasion and perinervous invasion were associated with poorer DFS (P<0.05). Three relevant independent predictors of poor DFS were identified in multivariate analysis, namely bowel obstruction (HR=2.46; 95%CI 1.31-4.62, P=0.005), vascular emboli (HR=2.79; 95%CI 1.74-4.47, P<0.001) and stage T4 (HR=2.16; 95%CI 1.31-3.56, P=0.002). CONCLUSIONS: Bowel obstruction, vascular emboli and stage T4 are independently associated with MSI CRC recurrence, suggesting that screening for vascular emboli in routine clinical practice may assist with adjuvant chemotherapy decision-making.

Phenotypic changes contributing to Enterobacter gergoviae biocide resistance.

UNLABELLED: Enterobacter gergoviae is a recurrent contaminant of cosmetic and hygiene products. To understand how this bacterium adapts to biocides, we studied Ent. gergoviae CIP 76.01 and its triclosan and Methylisothiazolinone-chloromethylisothiazolinone (MIT-CMIT) tolerant isogenic mutants. They were compared with others also isolated from contaminated cosmetics. Phenotypic differences were noted and these included changes in the bacterial envelope and flagella along with differences in motility, and biofilm growth rates. Triclosan and MIT-CMIT derivatives expressed flagella and other MIT-CMIT derivatives exhibited some external appendages. Those bacteria expressing a high-level minimal inhibitory concentration to MIT-CMIT, expressed a strong biofilm formation. No differential phenotypes were noted for carbon source utilisation. Enterobacter gergoviae demonstrated a diverse response to both of these preservatives contained in cosmetic preparations, depending on their concentrations. Interestingly, this adaptive response is associated with modifications of filament structure-related proteins contributing to increase the organism motility and the production of biofilm. SIGNIFICANCE AND IMPACT OF THE STUDY: Recurrent contaminations of cosmetics products by Ent. gergoviae, needed a better understanding concerning the bacterial adaptation to preservative agents, with particular concern to triclosan and MIT-CMIT. We demonstrated that bacteria response is associated to various mechanisms represented by expression of external appendages (pili or fimbriae) that control cell motility and biofilm formation and evolving as the concentration of biocides adaptation increased. Such mechanisms which are not chemical specific can also promote a cross-resistance to other biocidal agents. The characterization of Ent. gergoviae adaptability to biocides allows industry to adjust the ranges of concentrations and composition of preservatives in formula.

Enterobacter gergoviae adaptation to preservatives commonly used in cosmetic industry.

OBJECTIVE: The aim of this study was to obtain a better understanding regarding the origin of recurrent contamination by Enterobacter gergoviae in diverse cosmetic formula. We studied 65 isolates collected from various sources (clinical, food, cosmetics). METHODS: RAPD analysis using AP12H, REP and ERIC-PCR was carried out for epidemiological typing. Evaluation of susceptibility to preservatives currently used in cosmetics for a representative panel of collection strains was measured. Preservative efficacy was evaluated by minimum inhibitory concentrations and minimum bactericidal concentrations (MBCs). RESULTS: Eighty per cent of isolates was unrelated. E. gergoviae showed significant levels of resistance to preservatives. MBC was higher than maximum permitted concentrations imposed by European Commission (EC). Association of preservatives showed in rare case additive effects, and no synergic effects were observed. CONCLUSION: Most of the cosmetic formulations are contaminated with unrelated E. gergoviae strains. Maximum allowed concentrations for sodium benzoate are inefficient to limit proliferation and control adaptability to this bacterium in cosmetic products. Efflux mechanisms should be involved in methylisothiazolinone-chloromethylisothiazolinone and triclosan adaptation.

How to minimize toxic exposure to pyridine during continuous infusion of ceftazidime in patients with cystic fibrosis?

Ceftazidime is particularly efficient against Pseudomonas aeruginosa in cystic fibrosis patients. Thus, the spontaneous production of pyridine, which is a toxic product, raises some concern. Our aim was to examine the kinetics of degradation of ceftazidime in portable infusion pumps either at 4°C, 22°C, or 33°C and to propose some recommendations in order to reduce the pyridine exposure. Two administration models were studied in vitro. In model 1, we administered 12 g of ceftazidime infused over 23 h (once-daily infusion) compared to 6 g infused over 11.5 h in model 2 (twice-daily regimen). Samples were collected at 0 h and then every 4 and 2 h after the shaping of portable infusion pumps in models 1 and 2, respectively. Both ceftazidime and pyridine were analyzed using an ultraviolet high-performance liquid chromatograph. Production of pyridine is highly depending on the temperature. The in situ production of pyridine per day of treatment decreases at a ratio close to 1/6 and 1/3 between 33°C and 4°C in models 1 and 2, respectively. Regardless of the conditions, the production of pyridine is significantly lower in model 2, whereas the total delivery amount of ceftazidime is significantly higher at 4°C and 33°C compared to that in model 1. According to a the precautionary principle, these findings lead to three major recommendations: (i) exposing a solution of ceftazidime to over 22°C should be strictly avoided, (ii) a divided dose of 6 g over 11.5 h instead of a once-daily administration is preferred, and (iii) infusion should be administered immediately after reconstitution.

Natural extracts stimulate membrane-associated mechanisms of resistance in Gram-negative bacteria.

UNLABELLED: Several mechanisms are involved in the bacterial resistance towards antimicrobial agents. The membrane-associated mechanisms of resistance were studied in Escherichia coli strains after incubation with Thymus maroccanus essential oil, its major components (carvacrol and thymol) or with certain antibiotics. The minimum inhibitory concentration (MIC) and the expression of membrane proteins, porins and efflux pumps were determined in wild type and derivative strains. Derivative strains adapted to different compounds displayed a high level of resistance to all tested antibiotics. The MIC increase is associated with an overexpression of an efflux pump immunorelated to AcrAB-TolC in various variants. Interestingly, the expression of outer membrane proteins slightly decreases in these strains. We demonstrate that the increase in antibiotic resistance correlates with membrane changes observed in the variants. This type of bacterial adaptation to natural compounds can occur in vivo providing the emergence/selection of bacteria less susceptible to clinically used antibiotics. SIGNIFICANCE AND IMPACT OF THE STUDY: Thymus maroccanus essential oil and some major components are able to select variants that modify the expression of transporters involved in the influx (porins) and in the efflux (AcrAB family) of various drugs. Importantly, these membrane proteins are involved in the transport of natural compounds and several antibiotic families. This special 'membrane adaptation' can explain the persistence of less susceptible/tolerant bacteria in the environment where natural compounds are present and the continuous stimulation of efflux systems in these bacteria.

Effect of low-frequency KRAS mutations on the response to anti-EGFR therapy in metastatic colorectal cancer.

BACKGROUND: Only patients with wild-type (WT) KRAS tumors benefit from anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (Mabs) in metastatic colorectal cancer (mCRC). Pyrosequencing is now widely used for the determination of KRAS mutation burden and a conservative cut-off point of 10% has been defined. Up until now, the impact of low-frequency KRAS mutations (<10%) on the response to anti-EGFR Mabs has yet to be evaluated. PATIENTS AND METHODS: Tumors from patients receiving anti-EGFR Mabs based on a WT genotype for KRAS, as determined using direct sequencing, have been retrospectively analyzed by pyrosequencing. Patients were categorized as WT (no KRAS mutation) or low-frequency mutation when KRAS mutation was <10% (KRAS low MT). RESULTS: A total of 168 patients treated by anti-EGFR Mabs for mCRC were analyzed. According to pyrosequencing, 138 tumors remained KRAS WT, while 30 tumors were KRAS low MT. In the KRAS low MT and KRAS WT groups, the response rates were 6.7% and 37.0%, respectively, while stabilization amounted to 23.3% versus 32.6% and progression to 70% versus 29% (P < 0.01). Progression-free survival (PFS) was 2.7 ± 0.5 months for KRAS low MT and was 6.0 ± 0.3 months for KRAS WT (P < 0.01). CONCLUSIONS: These results appear to validate consideration of low-frequency KRAS mutation tumors as positive, and justify a large-scale prospective study.

Cross-resistance between biocides and antimicrobials: an emerging question.

The widespread use of biocides, and their resulting dissemination in the environment, can contribute to adaptations in bacteria leading to the development of low-level susceptibility to antibacterial agents. The mechanisms of resistance in bacteria are similar for both antimicrobials and biocides, and exposure to biocides can result in cross-resistance to antibacterial agents. Resistance mechanisms altering the activity of biocide and antibiotic molecules are discussed with regard to regulation and mode of action in the light of laboratory studies of induced resistance. It is clear that in order to preserve their activity and avoid the development of possible cross-resistance, prudent use of antibacterial agents is to be strongly recommended, not only in clinical settings but also in veterinary and agricultural and other applications.

Thymus maroccanus essential oil, a membranotropic compound active on Gram-negative bacteria and resistant isolates.

AIMS: The effects of Thymus maroccanus essential oil (EO) on the integrity of the cell membranes and the permeability of the outer membrane (OM) and inner membrane (IM) of Escherichia coli, Enterobacter aerogenes and Salmonella enterica Typhimurium were investigated. METHODS AND RESULTS: The bacterial release of intracellular proteins, cytoplasmic ß-galactosidase and periplasmic ß-lactamase induced by T. maroccanus EO was compared to the membranotropic activity of polymyxin B (PB) known as an effective permeabilizer of the membrane of Gram-negative bacteria. Results showed that T. maroccanus EO increased the permeability of the OM and IM of studied bacteria and induced the release of intracellular proteins into the external medium. CONCLUSIONS: The effect of T. maroccanus EO on the outer membrane was comparable to that of PB, and both T. maroccanus EO and PB induce similar levels of ß-lactamase release. In addition, it also promoted the release of the cytoplasmic ß-galactosidase. Moreover, the lipopolysaccharide molecules and the overexpression of efflux pumps seem to play a crucial role in the level of susceptibility of studied bacteria to the permeabilizing effect of T. maroccanus EO. SIGNIFICANCE AND IMPACT OF STUDY: These results demonstrate that T. maroccanus EO can restore antibiotic activity by targeting the two bacterial membranes and would be attractive candidates for developing new adjuvants for combating resistant Gram-negative bacteria.

[Patients with cerebrospinal fluid shunt: radiation during two years of follow-up]. / Irradiación en portadores de válvula de derivación de líquido cefalorraquídeo. Seguimiento a los 2 años.

BACKGROUND: Ionizing radiation due to diagnostic tests and treatment can contribute to the later development of cancer. The patients with cerebrospinal fluid shunts (CFS) are exposed to greater risk. OBJECTIVE: To estimate the cumulative radiation dose from radiological studies in children with CFS and to determine the potential factors associated with a high level of radiation. METHODS: Descriptive observational study. All children treated for hydrocephalus with a CFS between 2005 and 2006 were included. We registered the number of radiological examinations performed on these patients due to neurosurgical control or evaluation for possible shunt malfunction. The cumulative radiation dose from radiological studies was estimated for each patient. RESULTS: Thirty-six patients were included. The median patient age was 6.1 months (range: 20 days - 15.3 years). One hundred thirty-six CT scans were performed and 19 shunt series were done. The median patient radiation was 6.9 mSv (range: 0 to 28.6 mSv); 85% of examinations were performed for neurosurgical control. The median absorbed radiation dose was higher in patients who were evaluated for some possible shunt malfunction than in patients without a suspected shunt malfunction (9 mSv vs 5 mSv, p=0.02). CONCLUSION: The radiation exposure from radiological examinations performed on children with CFS was considerable. The use of non-ionizing techniques would help in the neurosurgical control of patients with CSF. The development of clinical-diagnostic scales could enable patients with increased risk of shunt malfunction to be selected before a radiological test was carried out.

Membrane permeability, a pivotal function involved in antibiotic resistance and virulence in Enterobacter aerogenes clinical isolates.

Imipenem-susceptible E. aerogenes isolates exhibiting extended spectrum ß-lactamases, target mutations and a basal efflux expression, were identified in five patients. After imipenem treatment, imipenem-intermediate susceptible (IMI-I) or resistant (IMI-R) isolates emerged in these patients. Alteration in porin synthesis and increase in efflux expression were observed in the IMI-I isolates whereas complete loss of the porins, LPS alteration and efflux overexpression were observed in the IMI-R isolates. Bacterial virulence of the strains was investigated by the Caenorhabditis elegans model. The IMI-R isolates were shown to be significantly less virulent than the IMI-susceptible or IMI-I isolates. The pleiotropic membrane alteration and its associated fitness burden exhibited by E. aerogenes isolates influence their antibiotic resistance and their virulence behaviour. These findings highlight the balance between the low permeability-related resistance and virulence and their relationships with the treatment of resistant pathogens.

Bacterial and fungal colonisation of peripheral intravenous catheters in dogs and cats.

OBJECTIVES: The purposes of this study were to determine the prevalence of intravenous catheter colonisation in a routine clinical setting, to identify pathogens involved and to explore factors associated with an increased risk of colonisation. METHODS: A prospective study of 100 peripherally placed intravenous catheters from 13 cats and 78 dogs was conducted. The distal two-thirds were removed and submitted for bacterial and fungal cultures. Antimicrobial susceptibility of each isolate was determined. RESULTS: Nineteen peripheral catheters were positive for microbiologic culture from 14 animals. Twenty organisms were isolated among which Staphylococcus species was the most common. Isolates displayed lower levels of resistance against the antimicrobial agents amoxicillin-clavulanate, cephalosporins and gentamicin than against other agents tested. Major risk factors predisposing to catheter-related colonisation included dextrose infusion, duration of catheter placement, local complications and immunosuppressive diseases or drugs. CLINICAL SIGNIFICANCE: In a routine clinical setting, the prevalence of microbial colonisation of peripheral intravenous catheters is comparable to that found in an intensive care unit. However, consequences on morbidity and mortality rates differ.

An original deal for new molecule: reversal of efflux pump activity, a rational strategy to combat gram-negative resistant bacteria.

The worldwide dissemination of «multi-drug resistant¼ (MDR) pathogens has severely reduced the efficacy of our antibiotic arsenal and increased the frequency of therapeutic failure. MDR bacteria over-express efflux pumps and this active mechanism can extrude all classes of antibiotics from the cell. It is necessary to clearly decipher the genetic, structural and functional aspects of this transport system in order to combat this polyselective mechanism. By understanding how efflux pumps work we may be able to develop a new group of antibacterial agents, collectively termed efflux reversals, including membrane permeabilisers, efflux pump inhibitors and flux-competitive agents, specific blockers, energy poisons, etc. Several chemical families of efflux pump inhibitors have been described and characterized. Among them several inhibitor compounds demonstrate efficient blocking of the efflux pump activity involved in the MDR phenotype as observed in many Gram-negative clinical isolates. This new family of molecules represents the first antibacterial class of compound specifically targeting active transport in the bacterial cell.

Antibacterial activity of some natural products against bacteria expressing a multidrug-resistant phenotype.

The present study assessed the antimicrobial activities of various natural products belonging to the terpenoids, alkaloids and phenolics against a collection of Gram-negative multidrug-resistant (MDR) bacteria. The results demonstrated that most of the compounds were extruded by bacterial efflux pumps. In the presence of the efflux pump inhibitor phenylalanine arginine ß-naphthylamide (PAßN), the activities of laurentixanthone B (xanthone), plumbagin (naphthoquinone), 4-hydroxylonchocarpin (flavonoid) and MAB3 (coumarin) increased significantly against all studied MDR bacteria. Laurentixanthone B, 4-hydroxylonchocarpin and MAB3 contained the same pharmacophoric moiety as plumbagin. This study indicates that the AcrAB-TolC (Enterobacteriaceae) and MexAB-OprM (Pseudomonas aeruginosa) efflux pumps are involved in resistance of Gram-negative bacteria to most of the natural products.

Physiological characterisation of the efflux pump system of antibiotic-susceptible and multidrug-resistant Enterobacter aerogenes.

Enterobacter aerogenes predominates amongst Enterobacteriaceae species that are increasingly reported as producers of extended-spectrum beta-lactamases. Although this mechanism of resistance to beta-lactams is important, other mechanisms bestowing a multidrug-resistant (MDR) phenotype in this species are now well documented. Amongst these mechanisms is the overexpression of efflux pumps that extrude structurally unrelated antibiotics prior to their reaching their targets. Interestingly, although knowledge of the genetic background behind efflux pumps is rapidly advancing, few studies assess the physiological nature of the overall efflux pump system of this, or for that matter any other, bacterium. The study reported here evaluates physiologically the efflux pump system of an E. aerogenes ATCC reference as well as two strains whose MDR phenotypes are mediated by overexpressed efflux pumps. The activities of the efflux pumps in these strains are modulated by pH and glucose, although the effects of the latter are essentially restricted to pH 8, suggesting the presence of two general efflux pump systems, i.e. proton-motive force-dependent and ABC transporter types, respectively.

An AcrAB-mediated multidrug-resistant phenotype is maintained following restoration of wild-type activities by efflux pump genes and their regulators.

In this study, we aimed to answer the following question: 'How does a bacterium become so resistant to a given antibiotic even though the levels of antibiotic to which it has become resistant remained constant in the patient?'Escherichia coli AG100 strain induced to high-level resistance due to overexpression of an AcrAB efflux pump was serially cultured in 10mg/L tetracycline for 60 passages. Between each passage it became increasingly resistant to tetracycline, beta-lactams and quinolones with concomitant restoration of wild-type AcrAB activity. Because the multidrug-resistant phenotype could not be reversed with transfer to drug-free medium or with efflux pump inhibitors, it may have resulted from activation of a 'mutator gene' system that reduced the 'energy consumption' associated with an overexpressed efflux pump system.

[Improvement of carbohydrate deficient transferrin measurement by capillary zone electrophoresis using immunosubtraction of immunoglobulins and transferrin]. / Intérêt de l'immunosoustraction des immunoglobulines et de la transferrine dans le dosage de la transferrine désialylée en électrophorèse capillaire.

CDT (Carbohydrate Deficient Transferrin) is considered as the most efficient biomarker of alcohol abuse available for routine use. Among the various methods developed for its measurement, capillary zone electrophoresis (CZE) on the multicapillary analyzer Capillarys2 provides high quality results at high throughput. However, the non CDT specific measurement of protein absorbance at 200 nm may bring abnormal profiles in samples from patients with high polyclonal immunoglobulin level or monoclonal component. We evaluated the automated immunosubtraction procedure developed by the manufacturer in 48 samples with abnormal electrophoretic profiles that potentially could interfere with CZE measurement of CDT. Elimination of the serum immunoglobulins raised the number of interpretable profiles from 19 (40%) to 37 (77%). The immunosubtraction procedure failed in samples with a monoclonal component present at a concentration > 60 g/L and in some samples harbouring a partially degraded C3 fraction. Six samples identified as genetic BC transferrin variants were also included in the study and submitted to an automated transferrin subtraction procedure to ascertain whether the additional peak were actually transferrin glycoforms. After treatment, two samples were classified as homozygote C for transferrin due to the persistence of one of the supposed transferrin peak. In conclusion, immunoglobulin and transferrin subtraction allow a better CDT measurement in most samples with interfering monoclonal components and avoid misclassification of suspected transferrin BC or CD variants.

A multicentric retrospective study of serum/plasma urea and creatinine concentrations in dogs using univariate and multivariate decision rules to evaluate diagnostic efficiency.

BACKGROUND: Urea and creatinine are the most frequently used indirect markers in plasma and serum of glomerular filtration rate in dogs. Both have been shown to lack sensitivity but their diagnostic efficiency for the diagnosis of kidney disease has been minimally investigated. OBJECTIVE: The purpose of this retrospective study was to investigate the influence of possible factors of variation on both analytes and to determine whether specific decision rules should be drawn up for subpopulations of dogs. METHODS: The results of urea and creatinine measurements, breed, sex, age, and health status (healthy, renal disease, or nonrenal disease) of 3822 dogs were collected from the archives of 5 veterinary clinics. Data were analyzed with univariate and multivariate decision rules with and without adjustment. RESULTS: There were significant effects and interactions of almost all of the sources of variation. Slight improvements in diagnostic efficiency were obtained by adjusting the decision rules to these sources of variations. Univariate decision rules gave approximately the same diagnostic efficiency for urea and creatinine concentrations, with sensitivity and specificity in the range of 70% and 90%, respectively, using the upper limit of the reference interval as the threshold value. Multivariate decision rules provided only minor improvements in diagnostic efficiency. CONCLUSION: Simultaneous measurement of both urea and creatinine is of limited diagnostic value over the analysis of a single variable. Creatinine is the preferred analyte as it is affected by fewer extrarenal factors of variation.

[Lentiviral vectors]. / Lentivecteur: l'anti-vecteur rétroviral ?

The recent advent of RNA interference has strongly stimulated the growing interest toward lentiviral vectors. This, plus the occurrence of several adverse effects in a clinical trial in which oncoretroviral vectors were employed, refocused the need for efficient tools allowing a stable in vivo gene transfer. The lentivectors were first developed in 1996 to address the poor efficiency of murine retroviral vectors to transduce arrested cells. Taking advantage of the accumulated experience in retroviral vector design, a rapid evolution of the structural form of the lentivectors converted this gene transfer agent into a very simple and popular tool. This rapidly led to several commercially available solutions. In the present review, more than a simple comparison to oncoretroviral vectors, we aimed at emphasizing the specific points that distinguish lentiviral vectors and confirm them as good and safe candidates for the clinical delivery of therapeutic genes.