Building a biopsychosocial model of cancer-related fatigue: the BIOCARE FActory cohort study protocol

Background

Cancer-related fatigue (CRF) is the most common side effect of cancer and cancer treatment. CRF prevalence is up to 50% in breast cancer patients and can continue several years after cancer remission. This persistent subjective sense of exhaustion is multifactorial. Numerous parameters have been evidenced to be related to CRF across biological, physical, psychological, social and/or behavioral dimensions. Although CRF has been studied for many years, the majority of previous studies focused on only one dimension, i.e., physical function. Moreover, few studies investigated CRF longitudinally with repeated measures. These are the two main obstacles that limit the understanding of CRF mechanisms. The purpose of this study is to create a biopsychosocial model of CRF with simultaneous and longitudinal anthropometric, clinical, biological, physical, psychological and sociological parameters.

Methods

BIOCARE FActory is a multicentric prospective study that will consist of an 18-month follow-up of 200 women diagnosed with breast cancer. Four visits will be scheduled at diagnosis, after treatments, and 12 and 18 months after diagnosis. The same procedure will be followed for each visit. Each session will be composed of anthropometric data collection, a semi-structured interview, cognitive tests, postural control tests, neuromuscular fatigability tests and a cardiorespiratory fitness test. Clinical and biological data will be collected during medical follow-ups. Participants will also complete questionnaires to assess psychological aspects and quality of life and wear an actigraphy device. Using a structural equation modeling analysis (SEM), collected data will build a biopsychosocial model of CRF, including the physiological, biological, psychological, behavioral and social dimensions of CRF.

Discussion

This study aims to highlight the dynamics of CRF and its correlates from diagnosis to post treatment. SEM analysis could examine some relations between potential mechanisms and CRF. Thus, the biopsychosocial model will contribute to a better understanding of CRF and its underlying mechanisms from diagnosis to the aftermaths of cancer and its treatments.

Trial registration

This study is registered at ClinicalTrials.gov (NCT04391543), May 2020.

Analyse des courriers de plainte adressés au service d’urgence d’un centre hospitalier général

Objectif : L’objectif principal de notre travail était d’analyser les courriers de plainte (CP) adressés à un service d’urgence (SU). L’objectif secondaire était de déterminer s’il existait une corrélation entre CP et temporalité de passage au SU.

Matériel et méthodes : Étude rétrospective monocentrique sur six ans portant sur les CP concernant les prises en charge en SU.

Résultats : Quatre-vingt-un CP ont été analysés, la moyenne annuelle et l’incidence étaient de 13,5 CP/an et de 5,5 CP/ 10 000 passages. L’incidence était de 3,5 CP/10 000 passages pour les enfants vs 6,1 CP/10 000 passages pour les adultes (p = 0,11). Le plaignant était la famille dans 44 CP (55 %) et le patient dans 34 CP (42 %). Il n’y avait pas de différence significative entre le jour et la nuit (5,7 CP/10 000 vs 4,8 CP/ 10 000 passages ; p = 0,57) ni entre horaires de garde et horaires hors garde (5,6 CP/10 000 vs 5,2 CP/10 000 passages ; p = 0,78). Nous avons dénombré 133 doléances, avec une cause médicale dans 64 CP (48 %), une cause organisationnelle dans 44 CP (33 %), une cause relationnelle dans 25 CP (19 %). Une indemnisation financière a été demandée dans 13 CP (16 %) et a été accordée pour deux dossiers (2 %). Aucun CP n’a entraîné de poursuite en justice.

Conclusion : L’incidence des CP de notre SU reste dans la moyenne basse des données retrouvées au niveau national et sans relation avec la temporalité du passage. L’analyse des CP permet d’améliorer la qualité de la prise en charge et de proposer des mesures correctives en relation avec la commission des usagers.

Biofilms in hospital effluents as a potential crossroads for carbapenemase-encoding strains

Bacterial resistance to carbapenem, which is mainly due to the successful dissemination of carbapenemase-encoding genes, has become a major health problem. Few studies have aimed to characterize the level of resistance in the environment, notably in hospital wastewater, which is a likely hotspot for exchange of antibiotic resistance genes. In this work, we looked for the presence of imipenem-resistant bacteria and imipenem in the effluent of the teaching hospital of Clermont-Ferrand, France. Selective growth of bacteria from 14-day old biofilms formed in the pipe sewer showed that 22.1% of the isolates were imipenem-resistant and identified as Aeromonas (n = 23), Pseudomonas (n = 10), Stenotrophomonas (n = 4) and Acinetobacter (n = 1). Fifteen of these strains harbored acquired carbapenemase-encoding genes bla_VIM (n = 11), bla_OXA-48 (n = 2), bla_GES (n = 1), bla_NDM (n = 1). All isolates also harbored associated resistances to aminoglycosides, fluoroquinolones and/or tetracyclin. S1-nuclease pulsed-field gel electrophoresis analysis of eight selected isolates showed that four of them harbored one to two plasmids of molecular weight between 48.5 Kb and 194 Kb. In vitro transformation assays evidenced the presence of bla_VIM and bla_NDM on plasmids with the bla_VIM harboring 80 Kb plasmid having conjugative capacity. The predicted environmental concentration of imipenem in the hospital effluent was 3.16 μg/L, suggesting that biofilm bacteria are subjected to sub-MICs of imipenem within the effluent. However, no imipenem molecule was detected in the hospital effluent, probably owing to its instability: in vitro assays indicated that imipenem's biological activity was no longer detectable after 45 h of storage. However, the predictive value of the hazard quotient relative to the development of resistance was >1.0 (HQr = 28.9 ± 1.9), which indicates a possible risk. The presence of carbapenemase-encoding genes in hospital effluent biofilm strains and their ability to transfer are therefore a potential hazard that should not be neglected and points to the need for monitoring antibiotic resistance in hospital wastewater.

Opposing effect of Lactobacillus on in vitro Klebsiella pneumoniae in biofilm and in an in vivo intestinal colonisation model

Beneficial bacteria represent potential sources of therapy, particularly in the battle against antibiotic-resistant pathogens. The Gram-negative bacillus Klebsiella pneumoniae is not only a paradigm of multi-resistant opportunistic pathogen, but it is also able to colonise the human intestine and displays a high capacity to form biofilm. In this study, the anti-biofilm activity of 140 neutralised Lactobacillus supernatants was assessed against K. pneumoniae. Among the 13 strains whose supernatant significantly impaired biofilm formation, Lactobacillus plantarum CIRM653 was selected because it was also able to impair K. pneumoniae preformed biofilm, independently of a bactericidal effect. Mixed K. pneumoniae/L. plantarum CIRM653 biofilms had reduced tridimensional structures associated with a significant decrease in K. pneumoniae biomass. Further investigation showed that L. plantarum CIRM653 supernatant induced transcriptional modifications of K. pneumoniae biofilm-related genes, including down-regulation of the quorum sensing-related lsr operons and over-expression of type 3 pili structure genes. Increased production of type 3 pili was validated by Western-blot, hemagglutination and adhesion assays. L. plantarum CIRM653 activity against K. pneumoniae was also assessed in a murine intestinal colonisation model: a constant faecal pathogen burden was observed, as against a gradual decrease in the control group. These results reveal that an in vitro a priori attracting anti-biofilm activity of Lactobacillus might be counterbalanced by an in vivo behaviour in a complex microbiota environment with potential deleterious dispersal of highly adherent K. pneumoniae cells, raising the question of the accuracy of in vitro assays in screening of beneficial microbes.

Chloroplast targeting of phytochelatin synthase in Arabidopsis: effects on heavy metal tolerance and accumulation

The enzymatically synthesized thiol peptide phytochelatin (PC) plays a central role in heavy metal tolerance and detoxification in plants. In response to heavy metal exposure, the constitutively expressed phytochelatin synthase enzyme (PCS) is activated leading to synthesis of PCs in the cytosol. Recent attempts to increase plant metal accumulation and tolerance reported that PCS over-expression in transgenic plants paradoxically induced cadmium hypersensitivity. In the present paper, we investigate the possibility of synthesizing PCs in plastids by over-expressing a plastid targeted phytochelatin synthase (PCS). Plastids represent a relatively important cellular volume and offer the advantage of containing glutathione, the precursor of PC synthesis. Using a constitutive CaMV 35S promoter and a RbcS transit peptide, we successfully addressed AtPCS1 to chloroplasts, significant PCS activity being measured in this compartment in two independent transgenic lines. A substantial increase in the PC content and a decrease in the glutathione pool were observed in response to cadmium exposure, when compared to wild-type plants. While over-expressing AtPCS1 in the cytosol importantly decreased cadmium tolerance, both cadmium tolerance and accumulation of plants expressing plastidial AtPCS1 were not significantly affected compared to wild-type. Interestingly, targeting AtPCS1 to chloroplasts induced a marked sensitivity to arsenic while plants over-expressing AtPCS1 in the cytoplasm were more tolerant to this metalloid. These results are discussed in relation to heavy metal trafficking pathways in higher plants and to the interest of using plastid expression of PCS for biotechnological applications.

Genome-wide transcriptome profiling of the early cadmium response of Arabidopsis roots and shoots

Transcriptional regulation in response to cadmium treatment was investigated in both roots and leaves of Arabidopsis, using the whole genome CATMA microarray containing at least 24,576 independent probe sets. Arabidopsis plants were hydroponically treated with low (5 microM) or high (50 microM) cadmium concentrations during 2, 6, and 30 hours. At each time point, Cd level was determined using ICP-AES showing that both plant tissues are able to accumulate the heavy metal. RT-PCR of eight randomly selected genes confirmed the reliability of our microarray results. Analyses of response profiles demonstrate the existence of a regulatory network that differentially modulates gene expression in a tissue- and kinetic-specific manner in response to cadmium. One of the main response observed in roots was the induction of genes involved in sulfur assimilation-reduction and glutathione (GSH) metabolism. In addition, HPLC analysis of GSH and phytochelatin (PC) content shows a transient decrease of GSH after 2 and 6 h of metal treatment in roots correlated with an increase of PC contents. Altogether, our results suggest that to cope with cadmium, plants activate the sulfur assimilation pathway by increasing transcription of related genes to provide an enhanced supply of GSH for PC biosynthesis. Interestingly, in leaves an early induction of several genes encoding enzymes involved in the biosynthesis of phenylpropanoids was observed. Finally, our results provide new insights to understand the molecular mechanisms involved in transcriptional regulation in response to cadmium exposure in plants.

Metal(loid)s and radionuclides cytotoxicity in Saccharomyces cerevisiae. Role of YCF1, glutathione and effect of buthionine sulfoximine

The presence of heavy metal(loid)s in soils and waters is an important issue with regards to human health. Taking into account speciation problems, in the first part of this report, we investigated under identical growth conditions, yeast tolerance to a set of 15 cytotoxic metal(loid)s and radionuclides. The yeast cadmium factor 1 (YCF1) is an ATP-Binding Cassette transporter mediating the glutathione detoxification of heavy metals. In the second part, metal(loid)s that could be handled by YCF1 and a possible re-localisation of the transporter after heavy metal exposure were evaluated. YCF1 and a C-terminal GFP fusion, YCF1-GFP, were overexpressed in wild-type and Deltaycf1 strains. Both forms were functional, conferring a tolerance to Cd, Sb, As, Pb, Hg but not to Ni, Zn, Cu, Ag, Se, Te, Cr, Sr, Tc, U. Confocal experiments demonstrated that during exposure to cytotoxic metals, the localisation of YCF1-GFP was restricted to the yeast vacuolar membrane. In the last part, the role of glutathione in this resistance mechanism to metal(loid)s was studied. In the presence of heavy metals, application of buthionine sulfoximine (BSO), a well-known inhibitor of gamma-glutamylcysteine synthetase, led to a decrease in the cytosolic pool of GSH and to a limitation of yeast growth. Surprisingly, BSO was able to phenocopy the deletion of gamma-glutamylcysteine synthetase after exposure to Cd but not to Sb or As. In the genetic context of gsh1 and gsh2 yeast mutants, the critical role of GSH for Cd, As, Sb and Hg tolerance was compared to that of wild-type and Deltaycf1.

Increased serum resistance in Klebsiella pneumoniae strains producing extended-spectrum beta-lactamases

The aim of this study was to determine whether there is an association between serum resistance, O serotypes, and the production of extended-spectrum beta-lactamases (ESBLs) in Klebsiella pneumoniae. Ninety ESBL-producing and 178 non-ESBL-producing K. pneumoniae isolates gathered in five European countries were O serotyped and tested for sensitivity to the serum's bactericidal effect. The frequency of serum-resistant isolates was higher among ESBL-producing strains (30%; 27/90 isolates) than among non-ESBL-producing strains (17.9%; 32/178 isolates) (P = 0.037; odds ratio [OR] = 1.96; 95% confidence interval [95% CI] = 1.08 to 3.53). Although O1 was the most common O serotype in both Klebsiella groups, its frequency among ESBL-producing strains was significantly higher (59%; 53/90 isolates) than among non-ESBL producers (36%; 64/178 isolates) (P = 0.0006; OR = 2.5; 95% CI = 1.52 to 4.29). Furthermore, the prevalence of the O1 serotype was higher among serum-resistant strains of both ESBL-producing (74%; 20/27isolates) and non-ESBL producers (75%; 24/32 isolates) than among serum-sensitive ESBL producers (52.4%; 33/63 isolates) and non-ESBL producers (27.4%; 40/146 isolates). Serum resistance among ESBL-producing strains (36%; 17/47 isolates) versus non-ESBL-producing strains (16%; 27/166 isolates) was also significantly higher after the exclusion of clonal strains (P = 0.0056; OR = 2.9; 95% CI = 1.41 to 6.01). Sixteen ESBL types were detected, among which the frequency of serum resistance was significantly lower among the SHV-producing strains (9/48 isolates) than among the TEM producers (16/35 isolates) (P = 0.016; OR = 3.65; CI = 1.3 to 9.7). Curing ESBL-coding plasmids did not influence the serum resistance of the bacteria; all six plasmid-cured derivatives maintained serum resistance. The present findings suggest that ESBL-producing strains have a greater pathogenic potential than non-ESBL-producing strains, but the linkage between O serotypes, serum resistance, and ESBL production remains unclear at this stage.

Factors associated with antimicrobial resistance among clinical isolates of Klebsiella pneumoniae: 1-year survey in a French university hospital

Klebsiella pneumoniae is an opportunistic pathogen responsible for nosocomial infections. Both resistance to multiple antibiotics and the expression of virulence factors are likely to be involved in the physiopathological process. In this study, 227 isolates of K. pneumoniae collected over a 1-year period in a teaching hospital in Clermont-Ferrand, France, were investigated for their antibiotic resistance pattern and the presence of several potential virulence traits. Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) indicated that most of the isolates were phylogenetically unrelated. When tested in an in vitro adhesion assay with Int-407 intestinal cells, the median adhesion index was 5.5x10(4) bacteria/cm(2) (range, 2.0x10(2)-3.4x10(5)). Isolates resistant to cefoxitin, chloramphenicol, and quinolones showed significantly lower adhesion indexes. The frequency of mutagenesis conferring resistance to rifampicin was low for most of the isolates. The median mutagenesis frequency was 1.0x10(-8) (range, 2.5x10(-9)-3.2x10(-6)) at 24 h and 1.1x10(-8) (range, 1.8x10(-9)-1.2x10(-5)) at 7 days. In contrast, isolates resistant to cefoxitin, chloramphenicol, and tetracycline showed a significantly greater ability to mutate. These results suggest a link between adhesion capabilities and resistance to certain antibiotics. They furthermore indicate that strains with a high mutagenesis capacity are more likely to acquire antibiotic resistance genes. The high pathogenicity island of Yersinia was detected in 16.3% of the strains and was more often associated with isolates resistant to nalidixic acid and augmentin.

Impairment of respiratory burst in polymorphonuclear leukocytes by extended-spectrum beta-lactamase-producing strains of Klebsiella pneumoniae

The ability of extended-spectrum beta-lactamase (ESBL)-producing and non-ESBL-producing Klebsiella pneumoniae strains to induce a respiratory burst in polymorphonuclear leukocytes (PMNLs) was investigated. Ninety ESBL-producing and 178 non-ESBL-producing Klebsiella pneumoniae isolates were serotyped and their ability to induce a respiratory burst in PMNLs tested by monitoring the cells' chemiluminescence (CL) response. The percentage of isolates inducing high levels of CL response (CL>75%) was significantly higher among non-ESBL producers (52%) than among ESBL producers (32.2%) ( P<0.0001; OR=3.396; 95%CI=2.036-5.664). The median CL response was significantly higher among the non-ESBL producers (76.9%) than among the ESBL producers (52.6%) ( P=0.034). The two groups did not differ in their ability to resist intracellular killing by PMNLs ( P>0.05), with strains inducing high levels of CL response having significantly lower survival rates (31.8% vs. 42.4%) than strains inducing low levels of CL response (164% vs. 200%) ( P<0.01). The frequencies of the K2 and the K25 serotypes were significantly higher among ESBL-producing strains (17.8% and 22.2%, respectively) than among the non-ESBL producers (6.2% and 1.7%, respectively) ( P=0.0057 and P<0.0001). Of the 77 Klebsiella K serotypes, 71 were detectable among the non-ESBL producers, but only 24 were detectable among the ESBL producers. ESBL-producing Klebsiella pneumoniae strains might have a greater pathogenic potential by virtue of their ability to escape the phagocytic activity of PMNLs.

Effect of Diuron on aquatic bacteria in laboratory-scale wastewater treatment ponds with special reference to Aeromonas species studied by colony hybridization

Six laboratory-scale wastewater treatment ponds were filled with sediment and water obtained from a reference pond (a wastewater treatment plant located in a rural environment at Montel-de-Gelat, Puy-de-Dôme, France). They were kept at 20 degrees C, with alternative light and dark periods (12 h-12 h), and fed with raw effluent supplied weekly. Three of them were treated with Diuron (dissolved in DMSO) at a final concentration 10 mg/l, while the other three received only DMSO. Physico-chemical parameters, total bacteria, cultivable bacteria, and Aeromonas spp. were measured periodically until 41 days after the Diuron contamination. Total bacteria were treated with 4,6-diamidino 2-phenylindole (DAPI) and counted by epifluoroscence microscopy. The cultivable bacteria were quantified on plate count agar medium and Aeromonas spp. using colony hybridization. In the contaminated pilots, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), suspended solids (SS), volatile suspended solids (VSS), ammonium, phosphorus, and bacteria increased, but dissolved oxygen decreased. The abundance of total bacteria, cultivable bacteria (multiplied by 30), and Aeromonas spp. increased for two weeks after Diuron introduction, reverting to initial values three weeks later. The percentage of cultivable bacteria relative to total bacteria was 0.2% in controls and 1.2% in treated pilots, while the percentage of Aeromonas spp. relative to cultivable bacteria decreased from 6-10% to 2%. Our results suggest that Diuron, which acts on the photosystem II of phototrophs, supports the development of cultivable bacteria through new carbon sources derived from the decomposition of photosynthetic micro-organisms, but does not specifically support Aeromonas spp.

Regenerative capacity of human satellite cells: the mitotic clock in cell transplantation

In this communication, we will review the problems caused by cell-mediated gene therapy, taking skeletal muscle as a physiological model. In particular we have utilised vectors transferring telomerase under the control of retroviral promoters into human satellite cells. The set of results presented here has several implications regarding gene therapy trials. Nevertheless, more experiments will be required to fully validate this cellular model and to use telomerase to safely extend the lifespan of putative gene therapy vectors.

LPS-induced immune response in Drosophila

The study of the regulation of the inducible synthesis of antimicrobial peptides in Drosophila melanogaster has established this insect as a powerful model in which to study innate immunity. In particular, the molecular characterization of the regulatory pathway controlling the antifungal peptide drosomycin has revealed the importance of Toll receptors in innate immunity. We report here that injection of LPS into flies induces an immune response, suggesting that LPS receptors are used in Drosophila to detect Gram-negative bacteria infection. We have identified in the recently sequenced genome of Drosophila eight genes coding for Toll-like receptors in addition to Toll, which may function as LPS receptors. However, overexpression of a selection of these genes in tissue-culture cells does not result in up-regulation of the antibacterial peptide genes. These results are discussed in light of the recent data from genetic screens aimed at identifying the genes controlling the antibacterial response in Drosophila.

Heterogeneity of Shiga toxin-producing Escherichia coli strains isolated from hemolytic-uremic syndrome patients, cattle, and food samples in central France

A detailed analysis of the molecular epidemiology of non-O157:H7 Shiga toxin-producing Escherichia coli (STEC) was performed by using isolates from sporadic cases of hemolytic-uremic syndrome (HUS), animal reservoirs, and food products. The isolates belonged to the O91 and OX3 serogroups and were collected in the same geographical area over a short period of time. Five typing methods were used; some of these were used to explore potentially mobile elements like the stx genes or the plasmids (stx(2)-restriction fragment length polymorphism [RFLP], stx(2) gene variant, and plasmid analyses), and others were used to study the whole genome (ribotyping and pulsed-field gel electrophoresis [PFGE]). The techniques revealed that there was great diversity among the O91 and OX3 STEC strains isolated in central France. A close relationship between strains of the same serotype having the same virulence factor pattern was first suggested by ribotyping. However, stx(2)-RFLP and stx(2) variant analyses differentiated all but 5 of 21 isolates, and plasmid analysis revealed further heterogeneity; a unique combination of characteristics was obtained for all strains except two O91:H21 isolates from beef. The latter strains were shown by PFGE to be the most closely related isolates, with >96% homology, and hence may be subtypes of the same strain. Overall, our results indicate that the combination of stx(2)-RFLP, stx(2) variant, and plasmid profile analyses is as powerful as PFGE for molecular investigation of STEC diversity. Finally, the non-O157:H7 STEC strains isolated from HUS patients were related to but not identical to those isolated from cattle and food samples in the same geographical area. The possibility that there are distinct lineages of non-O157:H7 STEC, some of which are more virulent for humans, should be investigated further.

Antibodies to the CFTR modulate the turgor pressure of guard cell protoplasts via slow anion channels

The plasma membrane guard cell slow anion channel is a key element at the basis of water loss control in plants allowing prolonged osmolite efflux necessary for stomatal closure. This channel has been extensively studied by electrophysiological approaches but its molecular identification is still lacking. Recently, we described that this channel was sharing some similarities with the mammalian ATP-binding cassette protein, cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel [Leonhardt, N. et al. (1999) Plant Cell 11, 1141-1151]. Here, using the patch-clamp technique and a bioassay, consisting in the observation of the change in guard cell protoplasts volume, we demonstrated that a functional antibody raised against the mammalian CFTR prevented ABA-induced guard cell protoplasts shrinking and partially inhibited the slow anion current. Moreover, this antibody immunoprecipitated a polypeptide from guard cell protein extracts and immunolabeled stomata in Vicia faba leaf sections. These results indicate that the guard cell slow anion channel is, or is closely controlled by a polypeptide, exhibiting one epitope shared with the mammalian CFTR.

Probiotic activities of Lactobacillus casei rhamnosus: in vitro adherence to intestinal cells and antimicrobial properties

The interest of probiotics as remedies for a broad number of gastrointestinal and other infectious diseases has gained wide interest over the last few years, but little is known about their underlying mechanism of action. In this study, the probiotic activities of a human isolate of Lactobacillus casei subsp. rhamnosus strain (Lcr35) were investigated. Using intestinal Caco-2 cell line in an in vitro model, we demonstrated that this strain exhibited adhesive properties. The inhibitory effects of Lcr35 organisms on the adherence of three pathogens, enteropathogenic Escherichia coli (EPEC), enterotoxigenic E. coli (ETEC) and Klebsiella pneumoniae, were determined. A decrease in the number of adhering pathogens was observed, using either preincubation, postincubation or coincubation of the pathogens with Lcr35. Moreover, the antibacterial activities of cell-free Lcr35 supernatant was examined against nine human pathogenic bacteria, ETEC, EPEC, K. pneumoniae, Shigella flexneri, Salmonella typhimurium, Enterobacter cloacae, Pseudomonas aeruginosa, Enterococcus faecalis and Clostridium difficile. The growth of all strains was inhibited, as measured by determining the number of viable bacteria over time, but no bactericidal activity was detected in this in vitro assay. Together, these findings suggest that this probiotic strain could be used to prevent colonization of the gastrointestinal tract by a large variety of pathogens.

Brucella abortus lipopolysaccharide in murine peritoneal macrophages acts as a down-regulator of T cell activation

Macrophages play a central role in host immune responses against pathogens by acting as both professional phagocytic cells and as fully competent APCs. We report here that the LPS from the facultative intracellular Gram-negative bacteria Brucella abortus interferes with the MHC class II Ag presentation pathway. LPS inhibits the capacity of macrophages to present hen egg lysozyme (HEL) antigenic peptides to specific CD4(+) T cells but not those of OVA to specific CD8(+) T cells. This defect was neither related to a decrease of MHC class II surface expression nor to a deficient uptake or processing of HEL. In addition, B. abortus LPS did not prevent the formation of SDS-resistant MHC class II complexes induced by HEL peptides. At the cell surface of macrophages, we observed the presence of LPS macrodomains highly enriched in MHC class II molecules, which may be responsible for the significant down-regulation of CD4(+) T cell activation. This phenomenon may account for the avoidance of the immune system by certain bacterial pathogens and may explain the immunosuppression observed in individuals with chronic brucellosis.

Skeletal muscle regeneration and the mitotic clock

Regeneration of muscle fibers following damage requires activation of quiescent satellite cells, their proliferation and finally their differentiation and fusion into multinucleated myotubes, which after maturation will replace the damaged fiber. The regenerative potential of human skeletal muscle will be determined, at least partly, by the proliferative capacity of the satellite cells. In this study, we have measured the proliferative life span of human satellite cells until they reach senescence. These analyses were performed on cell populations isolated from old and young donors as well as from one child suffering from Duchenne muscular dystrophy, where extensive regeneration had occurred. In order to see if there are any age-related changes in the myogenic program we have also compared the program of myogenic differentiation expressed by satellite cells from these subjects at different stages of their proliferative lifespan.

[Verotoxin-producing Escherichia coli infections: study of its prevalence in children in the Auvergne region]

Verotoxin producing Escherichia coli (VTEC) have been associated with disease outbreaks of diarrhea hemorrhagic colitis and hemolytic-uremic syndrome in humans. Contamination occurs mainly by ingestion of beef and dairy products, but water and person to person transmission have also been described. Most of the clinical signs are due to the production of Stx1 and/or Stx2 Shiga toxins, also called verotoxins. Other virulence factors include enterohemolysin, and the product of the eae gene, intimin, involved in the attaching and effacing adherence phenotype. The predominant serotype is O157:H7, but VTEC strains of more than one hundred serotypes can cause human disease. In order to determine the prevalence of VTEC infections among children in the central part of France, stool samples from hospitalized children were examined for stx1 and stx2 genes by using a polymerase chain reaction (PCR) technique. From October 1997 to September 1998, 658 stool samples were analysed: among them 19 (3%) were stx-PCR positive. Only 8 children out of 19 had diarrhea, and for 5 of them, an enteric pathogen other than VTEC was isolated. VTEC strains were isolated from 10 samples: most of the isolates did not produce verotoxins at a high level, and they did not belong to serotypes associated with pathogenicity, which might explain the absence of relationship between VTEC isolation and pathogenicity in our study.

Prevalence and characterization of Shiga toxin-producing Escherichia coli isolated from cattle, food, and children during a one-year prospective study in France

During a 1-year survey of Shiga toxin-producing Escherichia coli (STEC) prevalence in central France, 2,143 samples were investigated by PCR for Shiga toxin-encoding genes. A total of 330 (70%) of 471 fecal samples collected from healthy cattle at the Clermont-Ferrand slaughterhouse, 47 (11%) of 411 beef samples, 60 (10%) of 603 cheese samples, and 19 (3%) of 658 stool specimens from hospitalized children with and without diarrhea were positive for the stx gene(s). A STEC strain was isolated from 34% (162 of 471) of bovine feces, 4% (16 of 411) of beef samples, 1% (5 of 603) of cheese samples, and 1.5% (10 of 658) of stool specimens. Of the 220 STEC strains isolated, 34 (15%) harbored the stx(1) gene, 116 (53%) harbored the stx(2) gene, and 70 (32%) carried both the stx(1) and stx(2) genes. However, 32 (14.5%) were not cytotoxic for Vero cells. The eae gene, found in 12 (5%) of the 220 strains, was significantly associated with the stx(1) gene and with isolates from children. Sequences homologous to ehxA were found in 102 (46%) of the 220 strains. Thirteen serotypes, OX3:H2, O113:H21, O113:H4, OX3:H21, O6:H10, OX178:H19, O171:H2, O46:H38, O172:H21, O22:H16, O91:H10, O91:H21, and O22:H8, accounted for 102 (55%) of 186 typeable isolates, and only one strain (0.5% of the 186 STEC isolates from cattle), belonged to the O157:H7 serotype. We showed that the majority of the STEC isolates from cattle, beef, and cheese were not likely to be pathogenic for humans and that the STEC strains isolated from children in this study were probably not responsible for diarrheal disease. Finally, the strains associated with hemolytic-uremic syndrome in the same geographical area were shown to belong to particular subsets of the STEC population found in the bovine reservoir.

Klebsiella pneumoniae capsule expression is necessary for colonization of large intestines of streptomycin-treated mice

The role of the Klebsiella pneumoniae capsular polysaccharide (K antigen) during colonization of the mouse large intestine was assessed with wild-type K. pneumoniae LM21 and its isogenic capsule-defective mutant. When bacterial strains were fed alone to mice, the capsulated bacteria persisted in the intestinal tract at levels of 10(8) CFU/g of feces while the capsule-defective strain colonized at low levels, 10(4) CFU/g of feces. In mixed-infection experiments, the mutant was rapidly outcompeted by the wild type. In situ hybridization on colonic sections revealed that bacterial cells of both strains were evenly distributed in the mucus layer at day 1 after infection, while at day 20 the wild type remained dispersed and the capsule-defective strain was seen in clusters in the mucus layer. These results suggest that capsular polysaccharide plays an important role in the gut colonization ability of K. pneumoniae.

Interaction of Brucella abortus lipopolysaccharide with major histocompatibility complex class II molecules in B lymphocytes

Lipopolysaccharide (LPS), a major amphiphilic molecule located at the outer membrane of gram-negative bacteria, is a potent antigen known to induce specific humoral immune responses in infected mammals. LPS has been described as a polyclonal activator of B lymphocytes, triggering the secretion of antibodies directed against distinct sugar epitopes of the LPS chain. But, how LPS is handled by B cells remains to be fully understood. This task appears to be essential for a better knowledge of the anti-LPS humoral immune response. In this study, we examine the internalization of LPS and its interaction with antigen-presenting major histocompatibility complex (MHC) class II molecules in murine and human B-cell lines. By use of immunofluorescence, we observe that structurally different LPSs from Brucella and Shigella strains accumulate in an intracellular compartment enriched in MHC class II molecules. By use of immunoprecipitation, we illustrate that only Brucella abortus LPS associates with MHC class II molecules in a haplotype-independent manner. Taken together, these results raise the possibility that B. abortus LPS may play a role in T-cell activation.

[Rotavirus infection associated with adult thrombotic microangiopathy]

BACKGROUND

A preceding viral syndrome is classically cited as a triggering factor for thrombotic microangiopathy although only anecdotal reports of the causal agent have been documented.

CASE REPORT

An 84-year-old woman developed thrombotic microangiopathy secondary to diarrhea. An exhaustive etiological work-up documented the presence of Rotavirus alone in the fecal matter. The clinical course was favorable after 9 plasma exchanges using frozen fresh plasma and was associated with disappearance of the Rotavirus.

DISCUSSION

Enterohemorrhagic Escherichia coli is the most commonly identified infectious agent causing thrombotic microangiopathy. A small number of cases caused by viral agents (particularly retroviruses) have also been documented. To our knowledge, this is the first case attributable to a Rotavirus. In our case, the presence of the Rotavirus in the fecal matter and the favorable clinical course when the virus disappeared would be in favor of its causal role in the pathogenesis of thrombotic micorangiopathy.

Lysosomal accumulation and recycling of lipopolysaccharide to the cell surface of murine macrophages, an in vitro and in vivo study

In this study, we detailed in a time-dependent manner the trafficking, the recycling, and the structural fate of Brucella abortus LPS in murine peritoneal macrophages by immunofluorescence, ELISA, and biochemical analyses. The intracellular pathway of B. abortus LPS, a nonclassical endotoxin, was investigated both in vivo after LPS injection in the peritoneal cavity of mice and in vitro after LPS incubation with macrophages. We also followed LPS trafficking after infection of macrophages with B. abortus strain 19. After binding to the cell surface and internalization, Brucella LPS is routed from early endosomes to lysosomes with unusual slow kinetics. It accumulates there for at least 24 h. Later, LPS leaves lysosomes and reaches the macrophage cell surface. This recycling pathway is also observed for LPS released by Brucella S19 following in vitro infection. Indeed, by 72 h postinfection, bacteria are degraded by macrophages and LPS is located inside lysosomes dispersed at the cell periphery. From 72 h onward, LPS is gradually detected at the plasma membrane. In each case, the LPS present at the cell surface is found in large clusters with the O-chain facing the extracellular medium. Both the antigenicity and heterogenicity of the O-chain moiety are preserved during the intracellular trafficking. We demonstrate that LPS is not cleared by macrophages either in vitro or in vivo after 3 mo, exposing its immunogenic moiety toward the extracellular medium.

ATP binding cassette modulators control abscisic acid-regulated slow anion channels in guard cells

In animal cells, ATP binding cassette (ABC) proteins are a large family of transporters that includes the sulfonylurea receptor and the cystic fibrosis transmembrane conductance regulator (CFTR). These two ABC proteins possess an ion channel activity and bind specific sulfonylureas, such as glibenclamide, but homologs have not been identified in plant cells. We recently have shown that there is an ABC protein in guard cells that is involved in the control of stomatal movements and guard cell outward K+ current. Because the CFTR, a chloride channel, is sensitive to glibenclamide and able to interact with K+ channels, we investigated its presence in guard cells. Potent CFTR inhibitors, such as glibenclamide and diphenylamine-2-carboxylic acid, triggered stomatal opening in darkness. The guard cell protoplast slow anion current that was recorded using the whole-cell patch-clamp technique was inhibited rapidly by glibenclamide in a dose-dependent manner; the concentration producing half-maximum inhibition was at 3 &mgr;M. Potassium channel openers, which bind to and act through the sulfonylurea receptor in animal cells, completely suppressed the stomatal opening induced by glibenclamide and recovered the glibenclamide-inhibited slow anion current. Abscisic acid is known to regulate slow anion channels and in our study was able to relieve glibenclamide inhibition of slow anion current. Moreover, in epidermal strip bioassays, the stomatal closure triggered by Ca2+ or abscisic acid was reversed by glibenclamide. These results suggest that the slow anion channel is an ABC protein or is tightly controlled by such a protein that interacts with the abscisic acid signal transduction pathway in guard cells.

Characterization of enteroaggregative Escherichia coli isolates

Forty enteraggregative Escherichia coli (EAggEC) previously characterized by their ability to adhere to HEp-2 cells or/and their hybridization with the 1-kb EAggEC DNA probe were investigated for the presence of adherence factors and heat-stable enterotoxin (EAST1)-encoding genes. Only 45% of the isolates harbored the EAST1-encoding genes as detected by polymerase chain reaction. None of them hybridized with an AAF/II-encoding gene specific DNA probe and 35% (14/40) were positive in a PCR assay using primers specific for aggC, an accessory gene of the AAF/I-encoding operon. Cloning and sequence analysis of the aggA variant from one isolate, EAggEC 457, revealed 68.9% identity between its deduced amino acid sequence and those of the aggA product from the AAF/I-producing reference strain, E. coli 17.2. No major protein subunit was detected at the surface of EAggEC 457 compared to the bacterial surface extract of E. coli 17.2.

Consequences of reduction of Klebsiella pneumoniae capsule expression on interactions of this bacterium with epithelial cells

Most Klebsiella pneumoniae clinical isolates are fully encapsulated and adhere in vitro to intestinal cell lines with an aggregative pattern. In this study, the influence of the capsule on interactions with epithelial cells was investigated by creating an isogenic mutant defective in the synthesis of the capsule. Determination of the uronic acid content of bacterial extracts confirmed that the mutant did not produce capsular polysaccharides whereas, with the wild-type strain, the level of encapsulation was growth phase dependent and reached a maximum during the lag and early log phases. Assays performed with different epithelial cell lines, Int-407, A-549, and HEp-2, showed that the capsule-defective mutant demonstrated greater adhesion than did the wild-type strain and that the aggregative pattern was maintained, indicating that the capsule was not related to the adhesion phenotype. In contrast, when the mucus-producing HT-29-MTX cells were used, the encapsulated wild-type strain adhered more strongly than did the capsule-defective mutant. No invasion properties were observed with any of the capsular phenotypes or cell lines used. The K. pneumoniae adhesin CF29K was detected by Western blot analysis and enzyme-linked immunosorbent assay on the surface of transconjugants obtained after transfer of a conjugative plasmid harboring the CF29K-encoding genes into both the wild-type and the capsule-defective strains. The amounts of adhesin detected were greater in the capsule-defective background strain than in the wild-type encapsulated strain and were associated with an increase in the level of adhesion to Caco-2 cells. Moreover, RNA slot blot experiments showed that transcription of the adhesin-encoding gene was markedly increased in the capsule-defective mutant compared to the wild-type encapsulated background. These results suggest (i) that the capsule plays an active role during the initial steps of the pathogenesis by interacting with mucus-producing cells but is subsequently not required for the adhesin-related interaction with the epithelial cell surface and (ii) that the expression of the adhesin is modulated by the presence of a capsule at a transcriptional level.

[Intestinal complications of thrombotic microangiopathy in the adult. 4 cases and review of the literature]

We report four cases of adult thrombotic microangiopathy associating diarrhea with severe ischemic colitis. In one case, the intestinal complications was severe and diffuse ischemic colitis, in two cases an inaugural colonic perforation requiring colectomy and in the last case a massive mesenteric infarct. In three cases, histologic examination showed vessel occlusion with microthrombi. Despite treatment with plasma exchange and plasma infusion, death ensued in two cases. Principally described in childhood thrombotic microangiopathy, intestinal complications occur exceptionally in adult thrombotic microangiopathy and are associated with a poor prognosis. Inaugural ischemic colitis revealing an adult thrombotic microangiopathy is also uncommon and thrombotic microangiopathy could be evoked in all patients presenting acute ischemic colitis.

Pharmacological properties of slow anion currents in intact guard cells of Arabidopsis. Application of the discontinuous single-electrode voltage-clamp to different species

More electrophysiological studies have been carried out on guard cells than on any other cell type of vascular plants. The characterization of their ion channels has been achieved using mainly the whole-cell patch-clamp technique applied to guard-cell protoplasts. The aim of this study was to obtain recordings of ion channel currents in intact guard cells and especially of slow anion channels of Arabidopsis thaliana, a species of fundamental genetic interest. Application of the discontinuous single-electrode voltage-clamp technique enabled the first characterization of K+ currents in Commelina communis and of slow anion currents in C. communis and A. thaliana in intact guard cells to be made. Inward K+ channels from A. thaliana were inhibited by external application of tetraethylammonium (TEA) or Ca2+. In the presence of K+ channel blockers, slow anion channel currents were elicited in almost all guard cells tested and were confirmed by the application of anion channel blockers. In A. thaliana, only anthracene-9 carboxylic acid was able to inhibit slow anion currents, to promote stomatal opening in the dark and to reverse the effect of 25 microM abscisic acid under light. Use of a single microelectrode and preservation of cell integrity make this technique well suited for the study of ion channel regulation in species that have guard cell protoplasts with which it is difficult to form good seals.

Non-O157:H7 Stx2-producing Escherichia coli strains associated with sporadic cases of hemolytic-uremic syndrome in adults

From August 1996 to May 1997, six verotoxin-producing Escherichia coli (VTEC) strains were isolated from stool specimens of adults suffering from hemolytic-uremic syndrome (HUS). All the isolates were stx2 positive and belonged to different serotypes: O6:H4, O91:H10, O91:H21, O rough:H16, OX3:H-, and O nontypeable: H-. The enterohemolysin (Ehly)-encoding genes were detected in two isolates, and none of the isolates harbors the intimin (Eae)-encoding gene. These findings suggest that stx2-positive non-O157:H7 VTEC is a major cause of HUS in adults and that several sources of pathogens are responsible for local endemic infections.

Inhibitory effect of roxithromycin on adhesion of Klebsiella pneumoniae strains 3051, CF504 and LM21

The effect of subinhibitory concentrations of roxithromycin on the adhesion of three strains of Klebsiella pneumoniae to Int-407 cells was studied. Adherence was markedly inhibited and the effect was increased when roxithromycin was added to the cell culture medium rather than to the bacterial growth medium. Several assays were performed in order to understand the mechanism by which roxithromycin exerted this inhibitory effect. The greatest effect was obtained when roxithromycin was concentrated in the extracellular compartment; when roxithromycin was concentrated in the intracellular compartment, the inhibitory effect was reduced. The analysis of adhesion factors of bacteria showed that exposure to roxithromycin did not alter their apparent structure or quantity. Roxithromycin appears to interfere in the interaction between bacteria and eukaryotic receptors.

Cloning of AtMRP1, an Arabidopsis thaliana cDNA encoding a homologue of the mammalian multidrug resistance-associated protein

A cDNA encoding a putative ATP-binding cassette (ABC) transporter from Arabidopsis was cloned and sequenced based on an EST clone homologous to ABC sequences in other species. The cDNA is 5.5 kb long and contains an ORF encoding a 1623 amino acids protein. This sequence is the first MRP-like protein found in plants.

Evidence for the existence of a sulfonylurea-receptor-like protein in plants: modulation of stomatal movements and guard cell potassium channels by sulfonylureas and potassium channel openers

Limitation of water loss and control of gas exchange is accomplished in plant leaves via stomatal guard cells. Stomata open in response to light when an increase in guard cell turgor is triggered by ions and water influx across the plasma membrane. Recent evidence demonstrating the existence of ATP-binding cassette proteins in plants led us to analyze the effect of compounds known for their ability to modulate ATP-sensitive potassium channels (K-ATP) in animal cells. By using epidermal strip bioassays and whole-cell patch-clamp experiments with Vicia faba guard cell protoplasts, we describe a pharmacological profile that is specific for the outward K+ channel and very similar to the one described for ATP-sensitive potassium channels in mammalian cells. Tolbutamide and glibenclamide induced stomatal opening in bioassays and in patch-clamp experiments, a specific inhibition of the outward K+ channel by these compounds was observed. Conversely, application of potassium channel openers such as cromakalim or RP49356 triggered stomatal closure. An apparent competition between sulfonylureas and potassium channel openers occurred in bioassays, and outward potassium currents, previously inhibited by glibenclamide, were partially recovered after application of cromakalim. By using an expressed sequence tag clone from an Arabidopsis thaliana homologue of the sulfonylurea receptor, a 7-kb transcript was detected by Northern blot analysis in guard cells and other tissues. Beside the molecular evidence recently obtained for the expression of ATP-binding cassette protein transcripts in plants, these results give pharmacological support to the presence of a sulfonylurea-receptor-like protein in the guard-cell plasma membrane tightly involved in the outward potassium channel regulation during stomatal movements.

Enteroadherent Escherichia coli and diarrhea in children: a prospective case-control study

The relative contribution of diarrheagenic Escherichia coli was examined during a 1-year prospective study of hospitalized children in Clermont-Ferrand, France, including 220 case patients (with diarrhea) and 211 matched controls. Fecal isolates were characterized by means of their pattern of adherence to HEp-2 cells and by colony hybridization with DNA probes specific for the six categories of diarrheagenic E. coli. No enteroinvasive or enterotoxigenic E. coli isolates were isolated. Twenty-eight (6.5%) eae-positive isolates and 39 (9%) enteroaggregative E. coli isolates characterized with the aggregative adherence probe and/or by their adherence pattern were detected; they were equally distributed among the patients and the controls. Diffusely adhering E. coli was the predominant pathotype: 30.7% were detected by their adherence pattern and 13.7% were detected with the daaC probe. They were isolated with similar frequencies from the patients and the controls, thereby showing no association with diarrhea. However, daaC-positive strains were significantly associated with a past record of urinary tract infections. These results suggest that the diffusely adhering E. coli organisms isolated in the present study are not true intestinal pathogens but may be regarded as resident colonic strains.

Adhesive properties and antibiotic resistance of Klebsiella, Enterobacter, and Serratia clinical isolates involved in nosocomial infections

Intestinal colonization by Klebsiella, Enterobacter, and Serratia (KES) strains is a crucial step in the development of nosocomial infections. We studied the adhesive properties, antibiotic resistance, and involvement in colonization or infection of 103 KES clinical isolates: 30 Klebsiella pneumoniae (29%), 16 Klebsiella oxytoca (15%), 30 Enterobacter aerogenes (29%), 14 Enterobacter cloacae (14%), and 13 Serratia sp. (13%) isolates. Half of them were resistant to several antimicrobial agents, including aminoglycosides and beta-lactam antibiotics. A total of 27 of 30 K. pneumoniae isolates (90%) adhered to the human cell line Intestine-407 (Int-407), while none of the K. oxytoca or E. aerogenes isolates and only 2 of the E. cloacae isolates adhered. Three adhesive patterns were observed for K. pneumoniae: an aggregative adhesion in 57% of the isolates, a diffuse adhesion in only one isolate, and a new pattern, localized adhesion, in 30% of the isolates. While most of the sensitive strains adhered with the aggregative phenotype, the localized pattern was associated with resistant K. pneumoniae isolates producing the CAZ-5 beta-lactamase. Furthermore, 45% of such localized-adhesion isolates were involved in severe infections. The distributions of type 1 and type 3 fimbriae, enteroaggregative E. coli, and cf29, pap, and afa/Dr adhesin-encoding genes were determined by using specific DNA probes. No relationship was found between the adhesive pattern and the production of specific fimbriae, suggesting that several unrecognized adhesive factors are involved. Our study indicates that special adhesive properties associated with resistance to antimicrobial agents could account for the pathogenicity of certain nosocomial strains.

Mechanism of action of K channel openers on skeletal muscle KATP channels. Interactions with nucleotides and protons

The molecular mechanisms underlying the actions of K channel openers (KCOs) on KATP channels were studied with the patch clamp technique in excised inside-out patches from frog skeletal muscle fibers. Benzopyran KCOs (levcromakalim and SR 47063) opened channels partially blocked by ATP, ADP, or ATP gamma s, with and without Mg2+, but they had no effects in the absence of internal nucleotides, even after channel activity had significantly declined because of rundown. The effects of KCOs could therefore be attributed solely to a competitive interaction between KCOs and nucleotides, as confirmed by observations that ATP decreased the apparent affinity for KCOs and that, conversely, KCOs decreased ATP or ADP sensitivity. Protons antagonized the action of the non-benzopyran KCOs, pinacidil and aprikalim, by enhancing their dissociation rate. This effect resembled the effect of acidification on benzopyran KCOs (Forestier, C., Y. Depresle, and M. Vivaudou. FEBS Lett. 325:276-280, 1993), suggesting that, in spite of their structural diversity, KCOs could act through the same binding sites. Detailed analysis of the inhibitory effects of protons on channel activity induced by levcromakalim or SR 47063 revealed that, in the presence of 100 microM ATP, this effect developed steeply between pH 7 and 6 and was half maximal at pH 6.6. These results are in quantitative agreement with an allosteric model of the KATP channel possessing four protonation sites, two nucleotidic sites accessible preferentially to Mg(2+)-free nucleotides, and one benzopyran KCO site. The structural implications of this model are discussed.

Modification by protons of frog skeletal muscle KATP channels: effects on ion conduction and nucleotide inhibition

1. The molecular mechanisms underlying pH regulation of skeletal muscle ATP-sensitive K+ (KATP) channels were studied using the patch clamp technique in the inside-out configuration. Two effects of intracellular protons were studied in detail: the decrease in magnitude of single-channel currents and the increase in open probability (Po) of nucleotide-inhibited channels. 2. The pH dependence of inward unit currents under different ionic conditions was in poor agreement with either a direct block of the pore by protons or an indirect proton-induced conformational change, but was compatible with the protonation of surface charges located near the cytoplasmic entrance of the pore. This latter electrostatic mechanism was modelled using Gouy-Chapman-Stern theory, which predicted the data accurately with a surface charge density of about 0.1 negative elementary charges per square nanometre and a pK (pH value for 50% effect) value for protonation of these charges of 6.25. The same mechanism, i.e. neutralization of negative surface charges by cation binding, could also account for the previously reported reduction of inward unit currents by Mg2+. 3. Intracellular alkalization did not affect Po of the KATP channels. Acidification increased Po. In the presence of 0.1 mM ATP (no Mg2+), the channel activation vs. pH relationship could be fitted with a sigmoid curve with a Hill coefficient slightly above 2 and a pK value of 6. This latter value was dependent on the ATP concentration, decreasing from 6.3 in 30 microM ATP to 5.3 in 1 microM ATP. 4. Conversely, the channel inhibition vs. ATP concentration curve was shifted to the right when the pH was lowered. At pH 7.1, the ATP concentration causing half-maximal inhibition was about 10 microM. At pH 5.4, it was about 400 microM. The Hill coefficient values remained slightly below 2. Similar effects were observed when ADP was used as the inhibitory nucleotide. 5. These results confirm that a reciprocal competitive link exists between proton and nucleotide binding sites. Quantitatively, they are in full agreement with a steady-state model of a KATP channel possessing four identical protonation sites (microscopic pK, 6) allosterically connected to the channel open state and two identical nucleotide sites (microscopic ATP dissociation constant, approximately 30 microM) connected to the closed state.

Retrospective case-control study of diffusely adhering Escherichia coli and clinical features in children with diarrhea

A retrospective case-control study with a small population group revealed that, among clinical signs, vomiting but not diarrhea was significantly associated with the presence of diffusely adhering Escherichia coli (DAEC) in children suffering from gastroenteritidis (P < 0.05). Of the children carrying DAEC strains, those who were F1845 DNA probe positive had a significantly longer hospital stay than those who were F1845 DNA probe negative. We believe that the heterogeneity of DAEC strains is responsible for the discrepant results concerning their involvement in disease and that only some of these strains are really pathogenic for children.

Aggregative adherence of Klebsiella pneumoniae to human intestine-407 cells

Aggregative adhesion of Klebsiella pneumoniae LM3 to Intestine-407 (Int-407) cells was studied. Adhesive capacities were affected by the bacterial growth phase (with a maximum of adherence obtained during the exponential phase), temperature, multiplicity of infection, and length of incubation with Int-407 cells. Adhesion occurred through a cytochalasin D-sensitive process and was greatly reduced after treatment of Int-407 with cycloheximide, indicating that aggregative adhesion requires active participation of Int-407 cells. Transmission electron microscopy revealed that adherent bacteria were surrounded by a capsule-like material, apparently involved in both bacterium-Int-407 cell and bacterium-bacterium adherence. Examination with a scanning electron microscope showed interactions of intestinal cell microvilli with bacteria and formation in 3 h of a fibrous network within and around the bacterial clusters. We speculate that aggregative adhesion of K. pneumoniae mediated by a capsule-like extracellular material might explain the persistence of these strains inside the host gastrointestinal tract.

Internalin-mediated invasion of epithelial cells by Listeria monocytogenes is regulated by the bacterial growth state, temperature and the pleiotropic activator prfA

Entry of Listeria monocytogenes into epithelial cells requires expression of inIA, the first gene of an operon comprising two genes: inIA, which encodes internalin, a 800-amino-acid protein, and inIB, which encodes a 630-amino-acid protein. We report here that the inI locus is transcribed on two transcripts in constant relative ratio: a 5 kb transcript spanning inIA and inIB, and a 2.9 kb transcript that covers only inIA. The promoter is located 397 bp from the GTG initiator of inIA and displays in its -35 region a palindrome similar to that found in promoters controlled by the pleiotropic activator prfA. Transcription of the inI locus is, as are several other L. monocytogenes virulence genes, activated by prfA and regulated by temperature--with higher expression at 37 degrees C versus 25 degrees C--and bacterial growth state. It is maximal during exponential growth and correlates with maximal invasivity of the bacteria in the human epithelial cell line Caco-2. It also correlates with maximum amounts of internalin present on the bacterial surface. Internalin is also detected in substantial amounts in culture supernatants. Taken together, these data suggest that surface-bound internalin plays an important role in bacterial entry but do not exclude a role for the released form.

Intracellular protons control the affinity of skeletal muscle ATP-sensitive K+ channels for potassium-channel-openers

Levcromakalim, a potential antihypertensive agent, is known to activate potassium channels dependent on intracellular ATP (K-ATP channels). In inside-out patches excised from frog skeletal muscle, levcromakalim or a related compound, SR 47063, caused a strong and persistent activation of K-ATP channels at a cytoplasmic pH of 7.1. However, at pH 6, these activators could no longer affect the K-ATP currents. Conversely, in the continuous presence of activator, lowering pH from 7.1 to 6 returned channel activity to its level in pH 6 alone. After wash-out of the activator, recovery from activation took minutes at pH 7.1 but only seconds at pH 6, thus ruling out an effect of protons on the activators in solution. These experiments suggest that K-channel-activators are unable to bind to their receptor when it is protonated, and more generally, they provide evidence at the microscopic level for proton-induced allosteric modulation of drug-receptor interaction.

Modulation by Mg2+ and ADP of ATP-sensitive potassium channels in frog skeletal muscle

The patch-clamp technique was used to examine the action of intracellular magnesium ions and ADP in the absence of ATP on skeletal muscle ATP-sensitive potassium channels (K-ATP channels). Inside-out patches were excised from the membrane of sarcolemmal blebs which arise spontaneously without enzymatic treatment after a frog muscle fiber is split in half. In the absence of nucleotides, K-ATP channel open probability was not significantly affected by intracellular magnesium even at a concentration (20 mM) which fully blocks cardiac and pancreatic K-ATP channels. On the other hand, Mg2+ ions (10-20 mM) decreased both inward and outward unitary currents. The percent reduction in inward currents (about 8%) was independent of voltage while the reduction in outward currents was larger at higher voltages, suggesting that the former effect resulted from cancellation of surface charges and the latter from rapid channel block. With or without Mg2+, intracellular ADP could either stimulate or inhibit K-ATP channel activity. Low concentrations (1-100 microM) of ADP rapidly and reversibly increased average activity by a factor of 2 to 3. This activation was seen in half of the patches tested and was greater in the presence of mM Mg2+. High concentrations (> 100 microM) of ADP inhibited activity with a half-block concentration of 450 microM in 0 Mg2+, i.e., more than an order of magnitude the value for ATP. ADP inhibition, like ATP inhibition, was partially relieved by mM Mg2+, suggesting that the Mg(2+)-bound ADP forms are less effective than free ADP forms. During exercise, free ADP levels rise and ATP declines while remaining high.(ABSTRACT TRUNCATED AT 250 WORDS)

The synthesis and function of the Escherichia coli hemolysin and related RTX exotoxins

The RTX group of exotoxins represents a branch of a family of exoproteins produced by Gram-negative bacteria which share the properties of being secreted by a leader-independent pathway and a tandemly-repeated nine-amino-acid sequence that is responsible for calcium binding. The Escherichia coli hemolysin (HlyA) is the prototype for the RTX exotoxin family which includes the leukotoxins of Pasteurella haemolytica and Actinobacillus actinomycetemcomitans and hemolysins from four Gram-negative genera. A review of the genetics, synthesis, export and target cell reactivity of the E. coli hemolysin is given. An evolutionary tree of the RTX toxin family based on amino acid sequence similarity is presented.