Treatment of inflammatory bowel disease associated E. coli with ciprofloxacin and E. coli Nissle in the streptomycin-treated mouse intestine

Background

E. coli belonging to the phylogenetic group B2 are linked to Inflammatory Bowel Disease (IBD). Studies have shown that antimicrobials have some effect in the treatment of IBD, and it has been demonstrated that E. coli Nissle has prophylactic abilities comparable to 5-aminosalicylic acid (5-ASA) therapy in ulcerative colitis. The objective of this study was to test if ciprofloxacin and/or E. coli Nissle could eradicate IBD associated E. coli in the streptomycin-treated mouse intestine.

Results

After successful colonization with the IBD associated E. coli strains in mice the introduction of E. coli Nissle did not result in eradication of either IBD associated strains or an E. coli from a healthy control, instead, co-colonization at high levels were obtained. Treatment of mice, precolonized with IBD associated E. coli, with ciprofloxacin for three days alone apparently resulted in effective eradication of tested E. coli. However, treatment of precolonized mice with a combination of ciprofloxacin for 3 days followed by E. coli Nissle surprisingly allowed one IBD associated E. coli to re-colonize the mouse intestine, but at a level 3 logs under E. coli Nissle. A prolonged treatment with ciprofloxacin for 7 days did not change this outcome.

Conclusions

In the mouse model E. coli Nissle can not be used alone to eradicate IBD associated E. coli; rather, 3 days of ciprofloxacin are apparently efficient in eradicating these strains, but surprisingly, after ciprofloxacin treatment (3 or 7 days), the introduction of E. coli Nissle may support re-colonization with IBD associated E. coli.     

Mucin Dynamics in Intestinal Bacterial Infection

Background

Bacterial gastroenteritis causes morbidity and mortality in humans worldwide. Murine Citrobacter rodentium infection is a model for gastroenteritis caused by the human pathogens enteropathogenic Escherichia coli and enterohaemorrhagic E. coli. Mucin glycoproteins are the main component of the first barrier that bacteria encounter in the intestinal tract.

Methodology/Principal Findings

Using Immunohistochemistry, we investigated intestinal expression of mucins (Alcian blue/PAS, Muc1, Muc2, Muc4, Muc5AC, Muc13 and Muc3/17) in healthy and C. rodentium infected mice. The majority of the C. rodentium infected mice developed systemic infection and colitis in the mid and distal colon by day 12. C. rodentium bound to the major secreted mucin, Muc2, in vitro, and high numbers of bacteria were found in secreted MUC2 in infected animals in vivo, indicating that mucins may limit bacterial access to the epithelial surface. In the small intestine, caecum and proximal colon, the mucin expression was similar in infected and non-infected animals. In the distal colonic epithelium, all secreted and cell surface mucins decreased with the exception of the Muc1 cell surface mucin which increased after infection (p<0.05). Similarly, during human infection Salmonella St Paul, Campylobacter jejuni and Clostridium difficile induced MUC1 in the colon.

Conclusion

Major changes in both the cell-surface and secreted mucins occur in response to intestinal infection.     

Magnetic resonance imaging of tumors colonized with bacterial ferritin-expressing Escherichia coli

Background

Recent studies have shown that human ferritin can be used as a reporter of gene expression for magnetic resonance imaging (MRI). Bacteria also encode three classes of ferritin-type molecules with iron accumulation properties.

Methods and Findings

Here, we investigated whether these bacterial ferritins can also be used as MRI reporter genes and which of the bacterial ferritins is the most suitable reporter. Bacterial ferritins were overexpressed in probiotic E. coli Nissle 1917. Cultures of these bacteria were analyzed and those generating highest MRI contrast were further investigated in tumor bearing mice. Among members of three classes of bacterial ferritin tested, bacterioferritin showed the most promise as a reporter gene. Although all three proteins accumulated similar amounts of iron when overexpressed individually, bacterioferritin showed the highest contrast change. By site-directed mutagenesis we also show that the heme iron, a unique part of the bacterioferritin molecule, is not critical for MRI contrast change. Tumor-specific induction of bacterioferritin-expression in colonized tumors resulted in contrast changes within the bacteria-colonized tumors.

Conclusions

Our data suggest that colonization and gene expression by live vectors expressing bacterioferritin can be monitored by MRI due to contrast changes.     

E. coli Nissle 1917 Affects Salmonella adhesion to porcine intestinal epithelial cells

Background

The probiotic Escherichia coli strain Nissle 1917 (EcN) has been shown to interfere in a human in vitro model with the invasion of several bacterial pathogens into epithelial cells, but the underlying molecular mechanisms are not known.

Methodology/Principal Findings

In this study, we investigated the inhibitory effects of EcN on Salmonella Typhimurium invasion of porcine intestinal epithelial cells, focusing on EcN effects on the various stages of Salmonella infection including intracellular and extracellular Salmonella growth rates, virulence gene regulation, and adhesion. We show that EcN affects the initial Salmonella invasion steps by modulating Salmonella virulence gene regulation and Salmonella SiiE-mediated adhesion, but not extra- and intracellular Salmonella growth. However, the inhibitory activity of EcN against Salmonella invasion always correlated with EcN adhesion capacities. EcN mutants defective in the expression of F1C fimbriae and flagellae were less adherent and less inhibitory toward Salmonella invasion. Another E. coli strain expressing F1C fimbriae was also adherent to IPEC-J2 cells, and was similarly inhibitory against Salmonella invasion like EcN.

Conclusions

We propose that EcN affects Salmonella adhesion through secretory components. This mechanism appears to be common to many E. coli strains, with strong adherence being a prerequisite for an effective reduction of SiiE-mediated Salmonella adhesion.     

Toll-like Receptor Signaling Activation by Entamoeba histolytica Induces Beta Defensin 2 in Human Colonic Epithelial Cells: Its Possible Role as an Element of the Innate Immune Response

Background

Entamoeba histolytica, a protozoan parasite of humans, produces dysenteric diarrhea, intestinal mucosa damage and extraintestinal infection. It has been proposed that the intestinal microbiota composition could be an important regulatory factor of amebic virulence and tissue invasion, particularly if pathogenic bacteria are present. Recent in vitro studies have shown that Entamoeba histolytica trophozoites induced human colonic CaCo2 cells to synthesize TLR-2 and TLR-4 and proinflammatory cytokines after binding to the amebic Gal/GalNac lectin carbohydrate recognition domain. The magnitude of the inflammatory response induced by trophozoites and the subsequent cell damage were synergized when cells had previously been exposed to pathogenic bacteria.

Methodology/Principal Findings

We show here that E. histolytica activation of the classic TLR pathway in CaCo2 cells is required to induce β defensin-2 (HBD2) mRNA expression and production of a 5-kDa cationic peptide with similar properties to the antimicrobial HBD2 expressed by CaCo2 cells exposed to enterotoxigenic Escherichia coli. The induced peptide showed capacity to permeabilize membranes of bacteria and live trophozoites. This activity was abrogated by inhibition of TLR2/4-NFκB pathway or by neutralization with an anti-HBD2 antibody.

Conclusions/Significance

Entamoeba histolytica trophozoites bind to human intestinal cells and induce expression of HBD2; an antimicrobial molecule with capacity to destroy pathogenic bacteria and trophozoites. HDB2''s possible role as a modulator of the course of intestinal infections, particularly in mixed ameba/bacteria infections, is discussed.     

Immunomodulatory Effects of Escherichia coli ATCC 25922 on Allergic Airway Inflammation in a Mouse Model

Background

Hygiene hypothesis demonstrates that the lack of microbial exposure would promote the development of allergic airway disease (AAD). Therefore, the gut microbiota, including Escherichia coli (E. coli), would probably offer a potential strategy for AAD.

Objective

To investigate whether E. coli infection is able to suppress the induction of AAD and to elucidate the underlying mechanisms.

Methods

Nonpathogenic E. coli ATCC 25922 was infected by gavage before AAD phase in three patterns: 10⁸ or 10⁶ CFU in neonates or 10⁸ CFU in adults. Then mice were sensitized and challenged with ovalbumin (OVA) to induce allergic inflammation in both the upper and lower airways. Hallmarks of AAD, in terms of eosinophil infiltration and goblet cell metaplasia in subepithelial mucosa, Th2 skewing of the immune response, and levels of T regulate cells (Tregs), were examined by histological analysis, ELISA, and flow cytometry, respectively.

Results

E. coli, especially neonatally infected with an optimal dose, attenuated allergic responses, including a decrease in nasal rubbing and sneezing, a reduction in eosinophil inflammation and goblet cell metaplasia in subepithelial mucosa, decreased serum levels of OVA-specific IgE, and reduced Th2 (IL-4) cytokines. In contrast, this effect came with an increase of Th1 (IFN-r and IL-2) cytokines, and an enhancement of IL-10-secreting Tregs in paratracheal lymph nodes (PTLN).

Conclusion

E. coli suppresses allergic responses in mice, probably via a shift from Th1 to Th2 and/or induction of Tregs. Moreover, this infection is age- and dose-dependent, which may open up novel possibilities for new therapeutic interventions.     

Escherichia coli Nissle 1917 Targets and Restrains Mouse B16 Melanoma and 4T1 Breast Tumors through Expression of Azurin Protein

Many studies have demonstrated that intravenously administered bacteria can target and proliferate in solid tumors and then quickly be released from other organs. Here, we employed the tumor-targeting property of Escherichia coli Nissle 1917 to inhibit mouse B16 melanoma and 4T1 breast tumors through the expression of azurin protein. For this purpose, recombinant azurin-expressing E. coli Nissle 1917 was developed. The levels of in vitro and in vivo azurin secretion in the engineered bacterium were determined by immunochemistry. Our results demonstrated that B16 melanoma and orthotopic 4T1 breast tumor growth were remarkably restrained and pulmonary metastasis was prevented in immunocompetent mice. It is worth noting that this therapeutic effect partially resulted from the antitumor activity of neutrophils and lymphocytes due to inflammatory responses caused by bacterial infections. No toxicity was observed in the animal during the experiments. This study indicates that E. coli Nissle 1917 could be a potential carrier to deliver antitumor drugs effectively for cancer therapy.     

Probiotic Escherichia coli Nissle 1917 inhibits leaky gut by enhancing mucosal integrity

Background

Probiotics are proposed to positively modulate the intestinal epithelial barrier formed by intestinal epithelial cells (IECs) and intercellular junctions. Disruption of this border alters paracellular permeability and is a key mechanism for the development of enteric infections and inflammatory bowel diseases (IBDs).

Methodology and Principal Findings

To study the in vivo effect of probiotic Escherichia coli Nissle 1917 (EcN) on the stabilization of the intestinal barrier under healthy conditions, germfree mice were colonized with EcN or K12 E. coli strain MG1655. IECs were isolated and analyzed for gene and protein expression of the tight junction molecules ZO-1 and ZO-2. Then, in order to analyze beneficial effects of EcN under inflammatory conditions, the probiotic was orally administered to BALB/c mice with acute dextran sodium sulfate (DSS) induced colitis. Colonization of gnotobiotic mice with EcN resulted in an up-regulation of ZO-1 in IECs at both mRNA and protein levels. EcN administration to DSS-treated mice reduced the loss of body weight and colon shortening. In addition, infiltration of the colon with leukocytes was ameliorated in EcN inoculated mice. Acute DSS colitis did not result in an anion secretory defect, but abrogated the sodium absorptive function of the mucosa. Additionally, intestinal barrier function was severely affected as evidenced by a strong increase in the mucosal uptake of Evans blue in vivo. Concomitant administration of EcN to DSS treated animals resulted in a significant protection against intestinal barrier dysfunction and IECs isolated from these mice exhibited a more pronounced expression of ZO-1.

Conclusion and Significance

This study convincingly demonstrates that probiotic EcN is able to mediate up-regulation of ZO-1 expression in murine IECs and confer protection from the DSS colitis-associated increase in mucosal permeability to luminal substances.     

Enhancement of crystallinity of cellulose produced by <Emphasis Type="Italic">Escherichia coli</Emphasis> through heterologous expression of <Emphasis Type="Italic">bcsD</Emphasis> gene from <Emphasis Type="Italic">Gluconacetobacter xylinus</Emphasis>

Objectives

To evaluate the crystallinity index of the cellulose produced by Escherichia coli Nissle 1917 after heterologous expression of the cellulose synthase subunit D (bcsD) gene of Gluconacetobacter xylinus BPR2001.

Results

The bcsD gene of G. xylinus BPR2001 was expressed in E. coli and its protein product was visualized using SDS-PAGE. FTIR analysis showed that the crystallinity index of the cellulose produced by the recombinants was 0.84, which is 17% more than that of the wild type strain. The increased crystallinity index was also confirmed by X-ray diffraction analysis. The cellulose content was not changed significantly after over-expressing the bcsD.

Conclusion

The bcsD gene can improve the crystalline structure of the bacterial cellulose but there is not any significant difference between the amounts of cellulose produced by the recombinant and wild type E. coli Nissle 1917.

     

Visible light responsive photocatalyst induces progressive and apical-terminus preferential damages on Escherichia coli surfaces

Background

Recent research shows that visible-light responsive photocatalysts have potential usage in antimicrobial applications. However, the dynamic changes in the damage to photocatalyzed bacteria remain unclear.

Methodology/Principal Findings

Facilitated by atomic force microscopy, this study analyzes the visible-light driven photocatalyst-mediated damage of Escherichia coli. Results show that antibacterial properties are associated with the appearance of hole-like structures on the bacteria surfaces. Unexpectedly, these hole-like structures were preferentially induced at the apical terminus of rod shaped E. coli cells. Differentiating the damages into various levels and analyzing the percentage of damage to the cells showed that photocatalysis was likely to elicit sequential damages in E. coli cells. The process began with changing the surface properties on bacterial cells, as indicated in surface roughness measurements using atomic force microscopy, and holes then formed at the apical terminus of the cells. The holes were then subsequently enlarged until the cells were totally transformed into a flattened shape. Parallel experiments indicated that photocatalysis-induced bacterial protein leakage is associated with the progression of hole-like damages, further suggesting pore formation. Control experiments using ultraviolet light responsive titanium-dioxide substrates also obtained similar observations, suggesting that this is a general phenomenon of E. coli in response to photocatalysis.

Conclusion/Significance

The photocatalysis-mediated localization-preferential damage to E. coli cells reveals the weak points of the bacteria. This might facilitate the investigation of antibacterial mechanism of the photocatalysis.     

Colonization by non-pathogenic bacteria alters mRNA expression of cytochromes P450 in originally germ-free mice

Gut microbiota provides a wide range of beneficial function for the host and has an immense effect on the host’s health state. It has also been shown that gut microbiome is often involved in the biotransformation of xenobiotics; however, the molecular mechanisms of the interaction between the gut bacteria and the metabolism of drugs by the host are still unclear. To investigate the effect of microbial colonization on messenger RNA (mRNA) expression of liver cytochromes P450 (CYPs), the main drug-metabolizing enzymes, we used germ-free (GF) mice, lacking the intestinal flora and mice monocolonized by non-pathogenic bacteria Lactobacillus plantarum ^NIZO2877 or probiotic bacteria Escherichia coli Nissle 1917 compared to specific pathogen-free (SPF) mice. Our results show that the mRNA expression of Cyp1a2 and Cyp2e1 was significantly increased, while the expression of Cyp3a11 mRNA was decreased under GF conditions compared to the SPF mice. The both bacteria L. plantarum ^NIZO2877 and E. coli Nissle 1917 given to the GF mice decreased the level of Cyp1a2 mRNA and normalized it to the control level. On the other hand, the colonization by these bacteria had no effect on the expression of Cyp3a11 mRNA in the liver of the GF mice (which remained decreased). Surprisingly, monocolonization with chosen bacterial strains has shown a different effect on the expression of Cyp2e1 mRNA in GF mice. Increased level of Cyp2e1 expression observed in the GF mice was found also in mice colonized by L. plantarum ^NIZO2877; however, the colonization with probiotic E. coli Nissle 1917 caused a decrease in Cyp2e1 expression and partially restored the SPF mice conditions.     

Aldose reductase inhibition prevents metaplasia of airway epithelial cells

Background

Goblet cell metaplasia that causes mucus hypersecretion and obstruction in the airway lumen could be life threatening in asthma and chronic obstructive pulmonary disease patients. Inflammatory cytokines such as IL-13 mediate the transformation of airway ciliary epithelial cells to mucin-secreting goblet cells in acute as well as chronic airway inflammatory diseases. However, no effective and specific pharmacologic treatment is currently available. Here, we investigated the mechanisms by which aldose reductase (AR) regulates the mucus cell metaplasia in vitro and in vivo.

Methodology/Findings

Metaplasia in primary human small airway epithelial cells (SAEC) was induced by a Th2 cytokine, IL-13, without or with AR inhibitor, fidarestat. After 48 h of incubation with IL-13 a large number of SAEC were transformed into goblet cells as determined by periodic acid-schiff (PAS)-staining and immunohistochemistry using antibodies against Mucin5AC. Further, IL-13 significantly increased the expression of Mucin5AC at mRNA and protein levels. These changes were significantly prevented by treatment of the SAEC with AR inhibitor. AR inhibition also decreased IL-13-induced expression of Muc5AC, Muc5B, and SPDEF, and phosphorylation of JAK-1, ERK1/2 and STAT-6. In a mouse model of ragweed pollen extract (RWE)-induced allergic asthma treatment with fidarestat prevented the expression of IL-13, phosphorylation of STAT-6 and transformation of epithelial cells to goblet cells in the lung. Additionally, while the AR-null mice were resistant, wild-type mice showed goblet cell metaplasia after challenge with RWE.

Conclusions

The results show that exposure of SAEC to IL-13 caused goblet cell metaplasia, which was significantly prevented by AR inhibition. Administration of fidarestat to mice prevented RWE-induced goblet cell metaplasia and AR null mice were largely resistant to allergen induced changes in the lung. Thus our results indicate that AR inhibitors such as fidarestat could be developed as therapeutic agents to prevent goblet cell metaplasia in asthma and related pathologies.     

Epidemiology of Extended-Spectrum β-Lactamase Producing Escherichia coli in the Stools of Returning Japanese Travelers,and the Risk Factors for Colonization

Objective

Travel overseas has recently been considered a risk factor for colonization with drug-resistant bacteria. The purpose of this study was to establish the epidemiology and risk factors associated with the acquisition of drug-resistant bacteria by Japanese travelers.

Methods

Between October 2011 and September 2012, we screened the stools of 68 Japanese returning travelers for extended-spectrum β-lactamase (ESBL) producing Escherichia coli. All specimens were sampled for clinical reasons. Based on the results, the participants were divided into an ESBL-producing E. coli positive group (18 cases; 26%) and an ESBL-producing E. coli negative group (50 cases; 74%), and a case-control study was performed. Microbiological analyses of ESBL-producing strains, including susceptibility tests, screening tests for metallo-β-lactamase, polymerase chain reaction amplification and sequencing of bla _CTX-M genes, multilocus sequence typing, and whole genome sequencing, were also conducted.

Results

In a univariate comparison, travel to India was a risk factor (Odds Ratio 13.6, 95% Confidence Interval 3.0–75.0, p<0.0001). There were no statistical differences in the characteristics of the travel, such as backpacking, purpose of travel, interval between travel return and sampling stool, and duration of travel. Although 10 of 13 analyzed strains (77%) produced CTX-M-15, no ST131 clone was detected.

Conclusion

We must be aware of the possibilities of acquiring ESBL-producing E. coli during travel in order to prevent the spread of these bacteria not only in Japan but globally.     

Impact of the <Emphasis Type="Italic">rpoS</Emphasis> genotype for acid resistance patterns of pathogenic and probiotic <Emphasis Type="Italic">Escherichia coli</Emphasis>

Background  

Enterohemorrhagic E. coli (EHEC), a subgroup of Shiga toxin (Stx) producing E. coli (STEC), may cause severe enteritis and hemolytic uremic syndrome (HUS) and is transmitted orally via contaminated foods or from person to person. The infectious dose is known to be very low, which requires most of the bacteria to survive the gastric acid barrier. Acid resistance therefore is an important mechanism of EHEC virulence. It should also be a relevant characteristic of E. coli strains used for therapeutic purposes such as the probiotic E. coli Nissle 1917 (EcN). In E. coli and related enteric bacteria it has been extensively demonstrated, that the alternative sigma factor σ^S, encoded by the rpoS gene, acts as a master regulator mediating resistance to various environmental stress factors.     

Role of intestinal bacteria in gliadin-induced changes in intestinal mucosa: study in germ-free rats

Background and Aims

Celiac disease (CD) is a chronic inflammatory disorder of the small intestine that is induced by dietary wheat gluten proteins (gliadins) in genetically predisposed individuals. The overgrowth of potentially pathogenic bacteria and infections has been suggested to contribute to CD pathogenesis. We aimed to study the effects of gliadin and various intestinal bacterial strains on mucosal barrier integrity, gliadin translocation, and cytokine production.

Methodology/Principal Findings

Changes in gut mucosa were assessed in the intestinal loops of inbred Wistar-AVN rats that were reared under germ-free conditions in the presence of various intestinal bacteria (enterobacteria and bifidobacteria isolated from CD patients and healthy children, respectively) and CD-triggering agents (gliadin and IFN-γ) by histology, scanning electron microscopy, immunofluorescence, and a rat cytokine antibody array. Adhesion of the bacterial strains to the IEC-6 rat cell line was evaluated in vitro.Gliadin fragments alone or together with the proinflammatory cytokine interferon (IFN)-γ significantly decreased the number of goblet cells in the small intestine; this effect was more pronounced in the presence of Escherichia coli CBL2 and Shigella CBD8. Shigella CBD8 and IFN-γ induced the highest mucin secretion and greatest impairment in tight junctions and, consequently, translocation of gliadin fragments into the lamina propria. Shigella CBD8 and E. coli CBL2 strongly adhered to IEC-6 epithelial cells. The number of goblet cells in small intestine increased by the simultaneous incubation of Bifidobacterium bifidum IATA-ES2 with gliadin, IFN-γ and enterobacteria. B. bifidum IATA-ES2 also enhanced the production of chemotactic factors and inhibitors of metalloproteinases, which can contribute to gut mucosal protection.

Conclusions

Our results suggest that the composition of the intestinal microbiota affects the permeability of the intestinal mucosa and, consequently, could be involved in the early stages of CD pathogenesis.     

Comparative genome analysis identifies few traits unique to the Escherichia coli ST131 H30Rx clade and extensive mosaicism at the capsule locus

Background

E.coli ST131 is a globally disseminated clone of multi-drug resistant E. coli responsible for that vast majority of global extra-intestinal E. coli infections. Recent global genomic epidemiological studies have highlighted the highly clonal nature of this group of bacteria, however there appears to be inconsistency in some phenotypes associated with the clone, in particular capsule types as determined by K-antigen testing both biochemically and by PCR.

Results

We performed improved quality assemblies on ten ST131 genomes previously sequenced by our group and compared them to a new reference genome sequence JJ1886 to identify the capsule loci across the drug-resistant clone H30Rx. Our data shows considerable genetic diversity within the capsule locus of H30Rx clone strains which is mirrored by classical K antigen testing. The varying capsule locus types appear to be randomly distributed across the H30Rx phylogeny suggesting multiple recombination events at this locus, but that this capsule heterogeneity has little to no effect on virulence associated phenotypes in vitro.

Conclusions

Our data provides a framework for determining the capsular genetics of E. coli ST131 and further beyond to ExPEC strains, and highlights how capsular mosaicism may be an important strategy in becoming a successful globally disseminated human pathogen.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-830) contains supplementary material, which is available to authorized users.     

Attaching and Effacing Escherichia coli Downregulate DNA Mismatch Repair Protein In Vitro and Are Associated with Colorectal Adenocarcinomas in Humans

Background

Mucosa-associated Escherichia coli are frequently found in the colonic mucosa of patients with colorectal adenocarcinoma, but rarely in healthy controls. Chronic mucosal E. coli infection has therefore been linked to colonic tumourigenesis. E. coli strains carrying eae (encoding the bacterial adhesion protein intimin) attach intimately to the intestinal mucosa and are classed as attaching and effacing E. coli (AEEC). Enteropathogenic Escherichia coli (EPEC) are the most common form of AEEC identified in man. EPEC utilise a type III secretion system to translocate effector proteins into host cells and infection induces wide-ranging effects on the host cell proteome. We hypothesised that EPEC infection could influence molecular pathways involved in colorectal tumourigenesis.

Methodology/Principal Findings

When co-cultured with human colorectal cell lines, EPEC dramatically downregulated the expression of key DNA mismatch repair proteins MSH2 and MLH1 in an attachment specific manner. Cytochrome c staining and TUNEL analysis confirmed that this effect was not a consequence of apoptosis/necrosis. Ex vivo human colonic mucosa was co-cultured with EPEC and probed by immunofluorescence to locate adherent bacteria. EPEC entered 10% of colonic crypts and adhered to crypt epithelial cells, often in the proliferative compartment. Adenocarcinoma and normal colonic mucosa from colorectal cancer patients (n = 20) was probed by immunofluorescence and PCR for AEEC. Mucosa-associated E. coli were found on 10/20 (50%) adenocarcinomas and 3/20 (15%) normal mucosa samples (P<0.05). AEEC were detected on 5/20 (25%) adenocarcinomas, but not normal mucosa samples (P<0.05).

Significance/Conclusions

The ability of EPEC to downregulate DNA mismatch repair proteins represents a novel gene-environment interaction that could increase the susceptibility of colonic epithelial cells to mutations and therefore promote colonic tumourigenesis. The potential role of AEEC in colorectal tumourigenesis warrants further investigation.     

Phenotypic and Molecular Characterization of Extended-Spectrum Beta-Lactamase-Producing Escherichia coli in Bangladesh

Background

Resistance to cephalosporins in Enterobacteriaceae is mainly due to the production of extended-spectrum beta-lactamase (ESBL). Little is known about ESBL-producing bacteria in Bangladesh. Therefore, the study presents results of phenotypic and molecular characterization of ESBL-producing Escherichia coli from hospitals in Bangladesh.

Methods

A total of 339 E. coli isolated from patients with urinary tract and wound infections attending three different medical hospitals in urban and rural areas of Bangladesh between 2003–2007 were screened for ESBL-production by the double disk diffusion test. Isolates with ESBL-phenotype were further characterized by antibiotic susceptibility testing, PCR and sequencing of different β-lactamase and virulence genes, serotyping, and XbaI-macrorestriction followed by pulsed-field gel electrophoresis (PFGE).

Results

We identified 40 E. coli with ESBL phenotype. These isolates were resistant to ceftriaxone, ceftazidime, cefotaxime, aztreonam, cefepime, and nalidixic acid but remained susceptible to imipenem. All but one isolate were additionally resistant to ciprofloxacin, and 3 isolates were resistant to cefoxitin. ESBL genes of blaCTX-M-1-group were detected in all isolates; blaTEM-type and blaOXA-1-type genes were detected in 33 (82.5%) and 19 (47.5%) isolates, respectively. Virulence genes that are present in diarrhoeagenic E. coli were not found. Class-1 integron was present in 20 (50%) isolates. All the ESBL-producing E. coli isolates harbored plasmids ranging between 1.1 and 120 MDa. PFGE-typing revealed 26 different pulsotypes, but identical pulsotype showed 6 isolates of serotype O25:H4.

Conclusion

The prevalence of multidrug-resistant ESBL-producing E. coli isolates appears to be high and the majority of the isolates were positive for bla _CTX-M. Although there was genetic heterogeneity among isolates, presence of a cluster of isolates belonging to serotype O25:H4 indicates dissemination of the pandemic uropathogenic E. coli clone in Bangladesh.