Josée Harel

Université de Montréal, Montréal, Quebec, Canada

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Publications (172)514.33 Total impact

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    ABSTRACT: F1651 and the pyelonephritis-associated pili (Pap) are two members of the type P family of adhesive factors. They play a key role in establishing disease caused by Extra-intestinal pathogenic Escherichia coli (ExPEC) strains in animals and humans. Both F1651 andPap are under the control of an epigenetic and reversible switch that defines the number of fimbriated (ON) and afimbriated (OFF) cells within a clonal population. Using the Gfp reporter system, we monitored in vitro the level of fluorescence intensity corresponding to the F1651 and Pap fimbrial synthesis. Following individual Escherichia coli cells by flow cytometry and by real-time fluorescence microscopy, we identified cells associated with a low or high level of fluorescent intensity, and a large amount of cells with partial levels of fluorescence, mostly present in the F1651 system. This mixed population identified through fluorescent intensity could be attributed to the high switching rate previously observed in F1651-positive bacteria. The fimbrial heterogeneous phenotype for these ExPEC could represent increased fitness in unpredictable environments. Our study illustrates that within the large repertoire of fimbrial variants such as the well-characterized Pap, F1651 is an exquisite example of regulatory expression that arms the bacterium with strategies for surviving to more than one particular environment. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Infection and immunity. 02/2015;
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    ABSTRACT: Biofilm formation and host-pathogen interactions are frequently studied using multiwell plates; however, these closed systems lack shear force which is present at several sites in the host such as the intestinal and urinary tracts. Recently, microfluidic systems, which incorporate shear force and very small volumes, have been developed to provide cell biology models that resemble in vivo conditions. Therefore, the objective of this study was to determine if the BioFlux 200 microfluidic system could be used to study host-pathogen interactions and biofilm formation in pathogenic Escherichia coli. Strains of various pathotypes were selected to establish the growth conditions for the formation of biofilms in the BioFlux 200 system on abiotic (glass) or biotic (eukaryotic cell) surfaces. Biofilm formation on glass was observed for the majority of strains when these were grown in M9 media at 30°C but not in RPMI at 37°C. In contrast, HRT-18 cell monolayers enhanced binding and, in most cases, biofilm formation of pathogenic E. coli in RPMI at 37°C. As a proof a principle to screen mutants, the ability of a diffuse adherent E. coli mutant strain lacking AIDA-1, a known mediator of attachment, was assessed in our models. When compared to the parental strain, the mutant formed a thin biofilm on glass or isolated clusters on an HRT-18 monolayer. In conclusion, we describe a microfluidic method for high throughput screening, which could be used to identify novel factors involved in E. coli biofilm formation and host-pathogen interactions under shear force. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Applied and Environmental Microbiology 02/2015; · 3.95 Impact Factor
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    ABSTRACT: In developed countries, enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a leading cause of bloody diarrhea and renal failures in human. Understanding strategies employed by EHEC to colonize the intestine is of major importance since to date no cure exists to eradicate the pathogen. In this study, the adaptive response of EHEC to the intestinal milieu conditioned by a human microbiota was examined. A transcriptomic analysis was performed on the EHEC strain EDL933 incubated in vitro in the sterile-filtrated cecal content of human microbiota-associated rats (HMC) compared with EDL933 incubated in the sterile-filtrated cecal content of germ-free rat (GFC). EDL933 switches from a glycolytic metabolic profile in the GFC to an anaplerotic metabolic profile in HMC. The expression of several catabolism genes was strongly affected such as those involved in the utilization of sugars, glycerol, N-acetylneuraminic acid, amino acids and secondary metabolites. Interestingly, expression level of critical EHEC O157:H7 virulence genes including genes from the locus of enterocyte effacement was reduced in HMC. Altogether, these results contribute to the understanding of EHEC adaptive response to a digestive content and highlight the ability of the microbiota to repress EHEC virulence gene expression.
    Microbes and Infection 10/2014; 17(1). · 2.73 Impact Factor
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    ABSTRACT: CS31A, a K88-related surface antigen specified by the clp operon, is a member of the type P family of adhesive factors and plays a key role in the establishment of disease caused by septicaemic and enterotoxigenic Escherichia coli strains. Its expression is under the control of methylation-dependent transcriptional regulation for which the leucine-responsive regulatory protein (Lrp) is essential. CS31A is preferentially in the OFF state and exhibits distinct regulatory features compared to other P family members. In the present study, Surface Plasmon Resonance and DNAse I protection assays showed that Lrp binds to the distal moiety of the clp regulatory region with low micromolar affinity, as compared to the proximal moiety that exhibits stronger nanomolar affinity. Complex formation was also influenced by the addition of PapI or FooI, which increased the affinity of Lrp for the clp distal and proximal regions, and was required to induce phase variation. The influence of PapI or FooI, however, was predominantly associated with more of a complete shutdown of clp expression, in contrast to what has previously been observed with AfaF (a PapI ortholog). Taken together, this suggests that the preferential OFF state observed in CS31A cells is mainly due to the weak interaction of the leucine-responsive regulatory protein with the clp distal region and PapI homolog favors the OFF phase. Within the large repertoire of fimbrial variants in the P family, our study illustrates that having a fimbrial operon that lacks its own PapI ortholog makes it more flexibly regulated by other orthologs in the cell.
    Journal of Bacteriology 06/2014; · 2.69 Impact Factor
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    ABSTRACT: Enterohaemorrhagic Escherichia coli (EHEC) are responsible for outbreaks of food- and water-borne illness. The bovine gastrointestinal tract (GIT) is thought to be the principle reservoir of EHEC. Knowledge of the nutrients essential for EHEC growth and survival in the bovine intestine may help in developing strategies to limit their shedding in bovine faeces thus reducing the risk of human illnesses. To identify specific metabolic pathways induced in the animal GIT, the transcriptome profiles of EHEC O157:H7 EDL933 during incubation in bovine small intestine contents (BSIC) and minimal medium supplemented with glucose were compared. The transcriptome analysis revealed that genes responsible for the assimilation of ethanolamine, urea, agmatine and amino acids (Asp, Thr, Gly, Ser and Trp) were strongly up-regulated suggesting that these compounds are the main nitrogen sources for EHEC in BSIC. A central role for the gluconeogenesis pathway and assimilation of gluconeogenic substrates was also pinpointed in EHEC incubated in BSIC. Our results suggested that three amino acids (Asp, Ser and Trp), glycerol, glycerol 3-phosphate, L-lactate and C4-dicarboxylates are important carbon sources for EHEC in BSIC. The ability to use gluconeogenic substrates as nitrogen sources (amino acids) and/or carbon sources (amino acids, glycerol and lactate) may provide a growth advantage to the bacteria in intestinal fluids. Accordingly, aspartate (2.4 mM), serine (1.9 mM), glycerol (5.8 mM) and lactate (3.6 mM) were present in BSIC and may represent the main gluconeogenic substrates potentially used by EHEC. A double mutant of E. coli EDL933 defective for phosphoenolpyruvate synthase (PpsA) and phosphoenolpyruvate carboxykinase (PckA), unable to utilize tricarboxylic acid (TCA) intermediates was constructed. Growth competition experiments between EHEC EDL933 and the isogenic mutant strain in BSIC clearly showed a significant competitive growth advantage of the wild-type strain further illustrating the importance of the gluconeogenesis pathway in maintaining EHEC in the bovine GIT.
    PLoS ONE 06/2014; 9(6):e98367. · 3.53 Impact Factor
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    ABSTRACT: Bacterial pathogens, including those of humans, animals, and plants, encounter phosphate (Pi)-limiting or Pi-rich environments in the host, depending on the site of infection. The environmental Pi-concentration results in modulation of expression of the Pho regulon that allows bacteria to regulate phosphate assimilation pathways accordingly. In many cases, modulation of Pho regulon expression also results in concomitant changes in virulence phenotypes. Under Pi-limiting conditions, bacteria use the transcriptional-response regulator PhoB to translate the Pi starvation signal sensed by the bacterium into gene activation or repression. This regulator is employed not only for the maintenance of bacterial Pi homeostasis but also to differentially regulate virulence. The Pho regulon is therefore not only a regulatory circuit of phosphate homeostasis but also plays an important adaptive role in stress response and bacterial virulence. Here we focus on recent findings regarding the mechanisms of gene regulation that underlie the virulence responses to Pi stress in Vibrio cholerae, Pseudomonas spp., and pathogenic E. coli.
    Virulence 05/2014; 5(5). · 3.32 Impact Factor
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    ABSTRACT: Enterohemorrhagic Escherichia coli (EHEC), an emerging food- and water-borne hazard, is highly pathogenic to humans. In the environment, EHEC must survive phosphate (Pi) limitation. The response to such Pi starvation is an induction of the Pho regulon including the Pst system that senses Pi variation. The interplay between the virulence of EHEC, Pho-Pst system and environmental Pi remains unknown. To understand the effects of Pi deprivation on the molecular mechanisms involved in EHEC survival and virulence under Pho regulon control, we undertook transcriptome profiling of the EDL933 wild-type strain grown under high Pi and low Pi conditions and its isogenic ΔphoB mutant grown in low Pi conditions. The differentially expressed genes included 1067 Pi-dependent genes and 603 PhoB-dependent genes. Of these 131 genes were both Pi and PhoB-dependent. Differentially expressed genes that were selected included those involved in Pi homeostasis, cellular metabolism, acid stress, oxidative stress and RpoS-dependent stress responses. Differentially expressed virulence systems included the locus of enterocyte effacement (LEE) encoding the type-3 secretion system (T3SS) and its effectors, as well as BP-933W prophage encoded Shiga toxin 2 genes. Moreover, PhoB directly regulated LEE and stx2 gene expression through binding to specific Pho boxes. However, in Pi-rich medium, constitutive activation of the Pho regulon decreased LEE gene expression and reduced adherence to HeLa cells. Together, these findings reveal that EHEC has evolved a sophisticated response to Pi limitation involving multiple biochemical strategies that contribute to its ability to respond to variations in environmental Pi and to coordinating the virulence response.
    PLoS ONE 04/2014; 9(4):e94285. · 3.53 Impact Factor
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    ABSTRACT: To better understand E. coli O157:H7 on-farm transmission dynamics requires sensitive methods for quantification of a broad range of concentrations of target organisms. For this purpose, a multiplex real time PCR (qPCR) assay was developed for quantification of O157 E. coli from one gm fecal samples of cattle and other animal species, targeting the Shiga toxin genes (stx1 and stx2) and the O157 somatic antigen gene, per. The multiplex qPCR assay provided specific detection across a broad range of bacterial concentrations with a lower limit of detection (LOD) of 101 genome copies which is equivalent to 101 bacteria. However, the LOD, when direct qPCR was applied to quantification of the targets in the feces of dairy cattle, was 103 genome copies per gram of feces. Enumeration below the threshold for direct qPCR was performed using a modified Most Probable Numbers (mMPN) method whereby E. coli O157 in enriched samples was isolated using immunomagnetic bead separation (IMS) and detected using qPCR, thus reducing the time and logistic constraints of biochemical/serological/gel analysis. Application of the mMPN (IMS/qPCR) assay to samples that were negative when tested using direct qPCR alone permitted quantification of low levels of E. coli O157 below levels detectable with direct qPCR. The direct qPCR and mMPN (IMS/qPCR) assays were applied to fecal samples from dairy, beef, swine and poultry feces. This approach can be employed to gain a better understanding of the patterns of infection in animals for analysis of on-farm transmission dynamics, for evaluating the effects of on-farm control strategies and for risk assessment in public health.
    Journal of microbiological methods 04/2014; · 2.43 Impact Factor
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    ABSTRACT: Expression of genes of the locus of enterocyte effacement (LEE) is essential for adherence of enterohemorrhagic Escherichia coli (EHEC) to intestinal epithelial cells. Gut factors that may modulate LEE gene expression may therefore influence the outcome of the infection. Because nitric oxide (NO) is a critical effector of the intestinal immune response that may induce transcriptional regulation in enterobacteria, we investigated its influence on LEE expression in EHEC O157:H7. We demonstrate that NO inhibits the expression of genes belonging to LEE1, LEE4, and LEE5 operons, and that the NO sensor nitrite-sensitive repressor (NsrR) is a positive regulator of these operons by interacting directly with the RNA polymerase complex. In the presence of NO, NsrR detaches from the LEE1/4/5 promoter regions and does not activate transcription. In parallel, two regulators of the acid resistance pathway, GadE and GadX, are induced by NO through an indirect NsrR-dependent mechanism. In this context, we show that the NO-dependent LEE1 down-regulation is due to absence of NsrR-mediated activation and to the repressor effect of GadX. Moreover, the inhibition of expression of LEE4 and LEE5 by NO is due to loss of NsrR-mediated activation, to LEE1 down-regulation and to GadE up-regulation. Lastly, we establish that chemical or cellular sources of NO inhibit the adherence of EHEC to human intestinal epithelial cells. These results highlight the critical effect of NsrR in the regulation of the LEE pathogenicity island and the potential role of NO in the limitation of colonization by EHEC.
    PLoS Pathogens 01/2014; 10(1):e1003874. · 8.06 Impact Factor
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    ABSTRACT: A customized DNA microarray was designed to detect Escherichia coli virulence genes in addition to Gram-negative genes conferring resistance to antimicrobials belonging to the aminoglycoside, β-lactam, tetracycline, sulfonamide, phenicol, and quinolone families as well as to rifampin, erythromycin, trimethoprim, olaquindox, quaternary ammonium compound resistant determinant genes, and mobile genetic elements such as class 1, 2, 3 integrons and transposon Tn21. This microarray was applied in the genotyping of two collection strains coming from colibacillosis outbreaks in rabbit and cattle facilities located in Italy and Iran, respectively. For each collection, the positive gene distribution and frequency per encoded enzyme or protein involved in antimicrobial resistance was first determined. Thereafter, strains positive for integrons were matched with the presence of transposon Tn21 (tnpM gene) in order to highlight the genetic potential of resistance (multi-resistance) transferability in the examined strains. Fourteen of 26 strains in our rabbit E. coli collection were positive for a class 1 integron, six of which were associated with the tnpM gene and multidrug resistance-related genes to the aminoglycoside, tetracycline, and sulfonamide-trimethoprim antimicrobial families, prevalently. Class 1 and/or class 2 and 3 integrons were also detected in 23 out of 51 strains in our cattle E. coli collection, 13 of which were also positive for tnpM gene. The presence of multiple drug resistance involving the aminoglycoside, tetracycline, and sulfonamide antimicrobial families are positively associated with this tnpM gene group. Moreover, strains having positive genes for integrons and transposons were also carriers, to a lesser extent, of class A and/or class C β-lactamase (11 strains) and quinolone (9 strains) resistant genes. The DNA microarray used in this chapter has proven to be a powerful tool in determining the genetic profile of antimicrobial resistance in E. coli field strains. The DNA microarray technology may be an appropriate technology for inclusion in antimicrobial resistance monitoring programs because of its adaptability to and ease of data collection for any particular monitoring program. Furthermore, this technology could be used to assess the effectiveness of antimicrobial use-reduction plans or in comparative studies between traditional and antibiotic-free animal production systems.
    Microarrays: Principles, Applications and Technologies, Edited by James V Rogers, 01/2014: chapter 10: pages 187-210; Nova Science Publishers inc.., ISBN: 978-1-62948-669-7
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    ABSTRACT: Escherichia coli is a heterogeneous species that can be part of the normal flora of humans but also include strains of medical importance. Among pathogenic members, Shiga-toxin producing E. coli (STEC) are some of the more prominent pathogenic E. coli within the public sphere. STEC disease outbreaks are typically associated with contaminated beef, contaminated drinking water, and contaminated fresh produce. These water- and food-borne pathogens usually colonize cattle asymptomatically; cows will shed STEC in their feces and the subsequent fecal contamination of the environment and processing plants is a major concern for food and public safety. This is especially important because STEC can survive for prolonged periods of time outside its host in environments such as water, produce, and farm soil. Biofilms are hypothesized to be important for survival in the environment especially on produce, in rivers, and in processing plants. Several factors involved in biofilm formation such as curli, cellulose, poly-N-acetyl glucosamine, and colanic acid are involved in plant colonization and adherence to different surfaces often found in meat processing plants. In food processing plants, contamination of beef carcasses occurs at different stages of processing and this is often caused by the formation of STEC biofilms on the surface of several pieces of equipment associated with slaughtering and processing. Biofilms protect bacteria against several challenges, including biocides used in industrial processes. STEC biofilms are less sensitive than planktonic cells to several chemical sanitizers such as quaternary ammonium compounds, peroxyacetic acid, and chlorine compounds. Increased resistance to sanitizers by STEC growing in a biofilm is likely to be a source of contamination in the processing plant. This review focuses on the role of biofilm formation by STEC as a means of persistence outside their animal host and factors associated with biofilm formation.
    Frontiers in microbiology. 01/2014; 5:317.
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    ABSTRACT: Enterohaemorrhagic Escherichia coli (EHEC) are zoonotic pathogens transmitted to humans through contaminated water or bovine products. One of the strategies used by pathogenic bacteria to survive in aquatic environments is by using free-living amoebae as hosts. Acanthamoeba castellanii is an amoeba known to host several water-borne pathogens. This study investigates the survival of EHEC with A. castellanii, which could contribute to its spread and transmission to humans. We used a gentamicin protection assay as well as fluorescence and electron microscopy to monitor the intra-amoebae survival of EHEC O157:H7 over 24 hours. The results showed that EHEC were able to survive within A. castellanii and that this survival was reduced by Shiga-toxins (Stx) produced by EHEC. A toxic effect mediated by Stx was demonstrated by amoebae mortality and LDH release during co-culture of EHEC and amoeba. This work describes the ability of EHEC to survive within A. castellanii and this host-pathogen interaction is partially controlled by the Stx. Thus, this ubiquitous amoeba could represent an environmental niche for EHEC survival and transmission. This article is protected by copyright. All rights reserved.
    FEMS Microbiology Letters 04/2013; · 2.72 Impact Factor
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    ABSTRACT: This study identified and characterized EPEC in the Canadian food supply. Eighteen of 450 E. coli isolates from food animal sources were identified as aEPEC. Several aEPEC isolates possessed multiple virulence genes, exhibited adherence and A/E lesion formation, disrupted tight junctions, and were co-classified with the ExPEC and ETEC pathotypes.
    Applied and Environmental Microbiology 04/2013; · 3.95 Impact Factor
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    ABSTRACT: Abstract Campylobacter jejuni is an important worldwide foodborne pathogen commonly found as a commensal organism in poultry that can reach high numbers within the gut after colonization. Although information regarding some genes involved in colonization is available, little is known about their distribution in strains isolated specifically from chickens and whether there is a linkage between antimicrobial resistance (AMR) and colonization genes. To assess the distribution and relevance of genes associated with chicken colonization and AMR, a C. jejuni microarray was created to detect 254 genes of interest in colonization and AMR including variants. DNA derived from chicken-specific Campylobacter isolates collected in 2003 (n=29) and 2008 (n=28) was hybridized to the microarray and compared. Hybridization results showed variable colonization-associated gene presence. Acquired AMR genes were low in prevalence whereas chemotaxis receptors, arsenic resistance genes, as well as genes from the cell envelope and flagella functional groups were highly variable in their presence. Strains clustered into two groups, each linked to different control strains, 81116 and NCTC11168. Clustering was found to be independent of collection time. We also show that AMR weakly associated with the CJ0628 and arsR genes. Although other studies have implicated numerous genes associated with C. jejuni chicken colonization, our data on chicken-specific isolates suggest the opposite. The enormous variability in presumed colonization gene prevalence in our chicken isolates suggests that many are of lesser importance than previously thought. Alternatively, this also suggests that combinations of genes may be required for natural colonization of chicken intestines.
    Foodborne Pathogens and Disease 03/2013; · 2.28 Impact Factor
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    ABSTRACT: Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a foodborne pathogen that resists the acidic gastric environment, colonizes the gut epithelium, and causes hemorrhagic colitis and hemolytic–uremic syndrome, especially in children. The genomic island OI-47 of E. coli O157:H7 contains a gene, z1528, encoding an EAL-domain protein potentially involved in c-di-GMP hydrolysis that is absent in non-pathogenic E. coli. This gene, designated vmpA, is co-transcribed with ycdT, which is present in non pathogenic E. coli and encodes a diguanylate cyclase involved in c-di-GMP synthesis. To test for vmpA function, we constructed a vmpA knockout mutant. We also overexpressed vmpA, purified the VmpA protein and assayed for its activity in vitro. We found that VmpA possesses c-di-GMP phosphodiesterase activity and that the vmpA mutation results in increased biofilm formation, and reduced swimming motility, which is consistent with the function determined in vitro. Unexpectedly, suppressor mutations arise frequently in the vmpA background suggesting that VmpA plays an important regulatory role in E. coli O157:H7. These findings represent an example of remarkable flexibility in the organization of c-di-GMP signaling pathways in closely related species.
    Veterinary Immunology and Immunopathology 03/2013; 152(s 1–2):132–140. · 1.75 Impact Factor
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    ABSTRACT: Since its first description in 1982, the zoonotic life-threatening Shiga toxin-producing Escherichia coli O157:H7 has emerged as an important food- and water-borne pathogen that causes diarrhea, hemorrhagic colitis, and hemolytic-uremic syndrome in humans. In the last decade, increases in E. coli O157:H7 outbreaks were associated with environmental contamination in water and through fresh produce such as green leaves or vegetables. Both intrinsic (genetic adaptation) and extrinsic factors may contribute and help E. coli O157:H7 to survive in adverse environments. This makes it even more difficult to detect and monitor food and water safety for public health surveillance. E. coli O157:H7 has evolved behaviors and strategies to persist in the environment. © 2013 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.
    FEMS Microbiology Letters 01/2013; · 2.72 Impact Factor
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    ABSTRACT: Contamination of surface waters in developing countries is a great concern. Treated and untreated wastewaters have been discharged into rivers and streams, leading to possible waterborne infection outbreaks and may represent a significant dissemination mechanism of antibiotic resistance genes. In this study, the water quality of San Pedro River, the main river and pluvial collector of the Aguascalientes State, Mexico was assessed. Thirty sample locations were tested throughout the River. The main physicochemical parameters of water were evaluated. Results showed high levels of fecal pollution as well as inorganic and organic matter abundant enough to support the heterotrophic growth of microorganisms. These results indicate poor water quality in samples from different locations. One hundred and fifty Escherichia coli were collected and screened by PCR for several virulence genes. Isolates were classified as either pathogenic (n = 91) or commensal (n = 59). The disc diffusion method was used to determine antimicrobial susceptibility to 13 antibiotics. Fifty-two percent of the isolates were resistant to at least one antimicrobial agent and 30.6% were multi-resistant. Eighteen E. coli strains were quinolone resistant of which 16 were multi-resistant. Plasmid-mediated quinolone resistance (PMQR) genes were detected in 12 isolates. Mutations at the Ser-83→Leu and/or Asp-87→Asn in the gyrA gene were detected as well as mutations at the Ser-80→Ile in parC. An E. coli microarray (Maxivirulence V 3.1) was used to characterize the virulence and antimicrobial resistance genes profiles of the fluoroquinolone-resistant isolates. Antimicrobial resistance genes such as bla TEM, sulI, sulII, dhfrIX, aph3 (strA), and tet (B) as well as integrons were found in fluoroquinolone (FQ) resistance E. coli strains. The presence of potential pathogenic E. coli and antibiotic resistance in San Pedro River such as FQ resistant E. coli could pose a potential threat to human and animal health.
    Frontiers in Microbiology 01/2013; 4:147. · 3.94 Impact Factor
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    ABSTRACT: Escherichia coli is implicated in the pathogenesis of inflammatory bowel disease (IBD). Rifaximin, a non-absorbable derivative of rifampicin effective against E. coli, improves symptoms in mild-to-moderate IBD. However, rifaximin resistance can develop in a single step in vitro. We examined the prevalence and mechanisms of rifaximin resistance in 62 strains of E. coli isolated from the ileal mucosa of 50 patients (19 with ileal Crohn's disease [L1+L3], 6 with colonic Crohn's disease [L2], 13 with ulcerative colitis [UC], 4 with symptomatic non-IBD diagnoses [NI], and 8 healthy [H]). Resistance (MIC >1024 mg/L) was present in 12/48 IBD-associated ileal E.coli strains. Resistance correlated with prior rifaximin treatment (P < 0.00000001) but not with the presence of ileal inflammation (P = 0.73) or E. coli phylogroup. Mutations in a 1,057 bp region of rpoB, which encodes the bacterial target of rifaximin, were identified in 10/12 resistant strains vs. 0/50 sensitive strains (P < 0.000000001), and consisted of seven amino acid substitutions. The efflux pump inhibitor Phe-Arg-β-naphthylamide (PAβN) lowered the MIC of 9/12 resistant strains 8 to 128 fold. Resistance was stable in the absence of rifaximin in 10/12 resistant strains after 30 passages. We conclude that IBD-associated ileal E. coli frequently manifest resistance to rifaximin that correlates with prior rifaximin use, amino acid substitutions in rpoB, and activity of PAβN-inhibitable efflux pumps, but not with the presence of ileal inflammation or E. coli phylogroup. These findings have significant implications for treatment trials targeting IBD-associated E. coli.
    Antimicrobial Agents and Chemotherapy 11/2012; · 4.57 Impact Factor
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    Virulence 11/2012; 3(7). · 3.32 Impact Factor
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    ABSTRACT: Enterohemorrhagic Escherichia coli (EHEC) are involved in outbreaks of food-borne illness and transmitted to humans through bovine products or water contaminated by cattle feces. Microbial interaction is one of the strategies used by pathogenic bacteria to survive in the environment. Among protozoa, the free-living amoebae are known to host and protect several water-borne pathogens. In this study, the interaction between EHEC and the predacious protozoa Acanthamoeba castellanii was investigated. Using monoculture and cocultures, growth of both organisms was estimated for 3 weeks by total and viable cell counts. The numbers of EHEC were significantly higher when cultured with amoebae than without, and less EHEC shifted into a viable but nonculturable state in the presence of amoebae. Using several mutants, we observed that the Pho regulon is required for EHEC growth when cocultured with amoebae. In contrast, the Shiga toxins (Stx) were not involved in this association phenotype. Cocultures monitored by electron microscopy revealed a loss of the regular rod shape of EHEC and the secretion of multilamellar vesicles by the amoebae, which did not contain bacteria. As the interaction between A. castellanii and EHEC appears beneficial for bacterial growth, this supports a potential role for protozoa in promoting the persistence of EHEC in the environment.
    MicrobiologyOpen. 10/2012; 1(4).

Publication Stats

3k Citations
514.33 Total Impact Points


  • 1990–2014
    • Université de Montréal
      • • Department of Pathology and Microbiology
      • • Faculty of Veterinary Medicine
      Montréal, Quebec, Canada
    • Université du Québec à Montréal
      • Department of Psychology
      Montréal, Quebec, Canada
  • 2013
    • Autonomous University of Aguascalientes
      • Departamento de Morfología
      Aguascalientes, Aguascalientes, Mexico
  • 2012
    • Cornell University
      • Department of Clinical Sciences
      Ithaca, NY, United States
  • 1994–2009
    • McGill University
      • Department of Microbiology and Immunology
      Montréal, Quebec, Canada
  • 2008
    • Freie Universität Berlin
      • Institute of Microbiology and Epizootics
      Berlín, Berlin, Germany
    • National Institute of Animal Health
      Tsukuba, Ibaraki, Japan
    • McMaster University
      • Department of Biochemistry and Biomedical Sciences
      Hamilton, Ontario, Canada
  • 2006–2007
    • University of Saskatchewan
      • Vaccine and Infectious Disease Organization
      Saskatoon, Saskatchewan, Canada
    • Institut national de la recherche scientifique
      Québec, Quebec, Canada
  • 2003–2007
    • National Research Council Canada
      • Biotechnology Research Institute (BRI)
      Ottawa, Ontario, Canada
    • Centre de Développement du Porc du Québec Inc
      Montréal, Quebec, Canada
  • 2003–2005
    • Université Blaise Pascal - Clermont-Ferrand II
      Clermont, Auvergne, France
    • French National Institute for Agricultural Research
      Lutetia Parisorum, Île-de-France, France
  • 1987
    • Stanford University
      • Division of Infectious Diseases and Geographic Medicine
      Palo Alto, California, United States