Enteroaggregative Escherichia coli infection

Extracellular components in enteroaggregative Escherichia coli biofilm and impact of treatment with proteinase K, DNase or sodium metaperiodate

Enteroaggregative E. coli (EAEC) is a major cause of diarrhea worldwide. EAEC are highly adherent to cultured epithelial cells and make biofilms. Both adherence and biofilm formation rely on the presence of aggregative adherence fimbriae (AAF). We compared biofilm formation from two EAEC strains of each of the five AAF types. We found that AAF type did not correlate with the level of biofilm produced. Because the composition of the EAEC biofilm has not been fully described, we stained EAEC biofilms to determine if they contained protein, carbohydrate glycoproteins, and/or eDNA and found that EAEC biofilms contained all three extracellular components. Next, we assessed the changes to the growing or mature EAEC biofilm mediated by treatment with proteinase K, DNase, or a carbohydrate cleavage agent to target the different components of the matrix. Growing biofilms treated with proteinase K had decreased biofilm staining for more than half of the strains tested. In contrast, although sodium metaperiodate only altered the biofilm in a quantitative way for two strains, images of biofilms treated with sodium metaperiodate showed that the EAEC were more spread out. Overall, we found variability in the response of the EAEC strains to the treatments, with no one treatment producing a biofilm change for all strains. Finally, once formed, mature EAEC biofilms were more resistant to treatment than biofilms grown in the presence of those same treatments.

A Mini-Review of Enteroaggregative Escherichia coli with a Specific Target on the Virulence Factors Controlled by the AggR Master Regulator

Enteroaggregative Escherichia coli (EAEC) strains have been linked to several outbreaks of severe diarrhea around the world, and this bacterium is now commonly resistant to antibiotics. As part of the pathophysiology of EAEC, the characteristic pattern of adherence looks like stacked bricks on the intestinal epithelium. This phenotype depends on an aggregative adhesion plasmid (pAA), which codes for a regulatory protein named AggR. The AggR protein is a master regulator that transcriptionally actives the main virulence genes in this E. coli pathotype, such as those that encode the aggregative adhesion fimbriae, dispersin and its secretion apparatus, Aar regulatory protein, and type VI secretion system. Several reports have shown that AggR positively affects most EAEC virulence genes, functioning as a classic transcriptional activator in the promoter region of these genes, interacting with the RNA polymerase. This minireview article integrates the information about virulence determinants of EAEC controlled by the AggR regulator.

A gastroenteritis outbreak associated with drinking water in a college in northwest China

An acute gastroenteritis outbreak occurred at a private college in June 2014 in northwest China. This outbreak involved two teachers and 629 students (range: 17-27 years, average 21.3 years). The main symptoms included non-bloody watery diarrhea, stomach ache, nausea, and vomiting, and the duration of illness ranged from 1 to 7 days. Eight of 18 water samples were disqualified. Thirty-four norovirus (NoV) RNA-positive samples were identified from 48 stool-related samples (genotyping results: 13 GII, 13 GI and 8 GI + GII mixture). Fourteen NoV samples were successfully characterized for genotype, including two GII.6, five GI.6, four GI.3, and three GI.1. Enteropathogenic Escherichia coli (EPEC) and enteroadherent Escherichia coli (EAEC) DNA was detected from patient stool specimens and water samples from well one; two EAEC strains and one EPEC strain were isolated from patient stool specimens. The risk ratios (RRs) associated with wells one and two were 1.66 and 1.49, respectively, and the RR associated with living in north dormitory building one was 2.59. The patients' epidemiological characteristics, symptoms, and duration of illness indicated that NoV-contaminated water might be the origin of this outbreak, and RR analysis suggested that the two wells were linked to the outbreak.

Prevalence of Diarrheagenic Escherichia coli in Foods and Fecal Specimens Obtained from Cattle, Pigs, Chickens, Asymptomatic Carriers, and Patients in Osaka and Hyogo, Japan

The source and routes of diarrheagenic Escherichia coli (DEC) remain poorly understood. To investigate the involvement of domestic animals in the dissemination of DEC, the prevalence of DEC in foods and fecal specimens from cattle, pigs, chickens, healthy carriers, and patients in Osaka and Hyogo, Japan was investigated using a multiplex real-time Polymerase Chain Reaction assay. The most abundant virulence genes were astA and eae, which had a prevalence 46.8% and 27.4%, respectively. Additionally, stx1 (26.6%) and stx2 (45.9%) were prevalent in cattle feces, while est (8.5%) and elt (7.6%) were prevalent in pig feces. afaB was the second-most prevalent gene in patients and healthy carriers, and it had detection rates of 5.1% and 8.1%, respectively. In contrast, afaB was not detected in animal feces or foods, except for three porcine fecal samples. The aggR gene was more prevalent in humans than in foods or animal feces. Both Shiga toxin-producing E. coli and atypical enteropathogenic E. coli carried by cattle may be sources for diarrheal diseases in humans. Pigs may be a source for human enterotoxigenic E. coli infections, whereas humans are expected to be the reservoir for diffusely adhering E. coli, enteroaggregative E. coli, and enteroinvasive E. coli.

The Role of Fibronectin in the Adherence and Inflammatory Response Induced by Enteroaggregative Escherichia coli on Epithelial Cells

Enteroaggregative Escherichia coli (EAEC) infections are still one of the most important etiologic pathogens of diarrhea in children worldwide. EAEC pathogenesis comprises three stages: adherence and colonization, production of toxins, and diarrhea followed by inflammation. Previous studies have demonstrated that EAEC strains have the ability to bind to fibronectin (FN); however, the role this extracellular matrix protein plays in the inflammatory response induced by EAEC remains unknown. In this study, we postulated that FN-mediated adherence of EAEC strains to epithelial cells increases the expression of pro-inflammatory genes. To verify this hypothesis, we infected HEp-2 and HT-29 cells, in both the presence and absence of FN, with EAEC reference strain 042. We quantified IL-8 secretion and the relative expression of a set of genes regulated by the NF-κB pathway. Although FN increased EAEC adherence, no changes in IL-8 protein secretion or IL8 gene expression were observed. Similar observations were found in HEp-2 cells transfected with FN-siRNA and infected with EAEC. To evaluate the involvement of AAF/II fimbriae, we infected HEp-2 and HT-29 cells, in both the presence and absence of FN, with an EAEC 042aafA mutant strain transformed with a plasmid harboring the native aafA gene with a site-directed mutation in Lys72 residue (K72A and K72R strains). No changes in IL-8 secretion were observed. Finally, SEM immunogold assay of cells incubated with FN and infected with EAEC revealed that AAF fimbriae can bind to cells either directly or mediated by FN. Our data suggests that FN participates in AAF/II fimbriae-mediated adherence of EAEC to epithelial cells, but not in the inflammatory response of cells infected by this pathogen.

Antibacterial and cell penetrating effects of LFcin17-30, LFampin265-284, and LF chimera on enteroaggregative Escherichia coli

Lactoferrin (LF) is a protein with antimicrobial activity, which is conferred in part by 2 regions contained in its N-terminal lobe. These regions have been used to develop the following synthetic peptides: lactoferricin17-30, lactoferrampin265-284, and LF chimera (a fusion of lactoferricin17-30 and lactoferrampin265-284). We have reported that these LF peptides have antibacterial activity against several pathogenic bacteria; however, the exact mechanism of action has not been established. Here, we report the effects of LF peptides on the viability of enteroaggregative Escherichia coli (EAEC) and the ability of these peptides to penetrate into the bacteria cytoplasm. The viability of EAEC treated with LF peptides was determined via enumeration of colony-forming units, and the binding and internalization of the LF peptides was followed via immunogold labeling and electron microscopy. Treatment of EAEC with 20 and 40 μmol/L LF peptides reduced bacterial growth compared with untreated bacteria. Initially the peptides associated with the plasma membrane, but after 5 to 30 min of incubation, the peptides were found in the cytoplasm. Remarkably, bacteria treated with LF chimera developed cytosolic electron-dense structures that contained the antimicrobial peptide. Our results suggest that the antibacterial mechanism of LF peptides on EAEC involves their interaction with and penetration into the bacteria.

Pet serine protease from enteroaggregative Escherichia coli stimulates the inflammatory response activating human macrophages

Background

Pet is a toxin from the family of Serine Protease Autotransporters of Enterobacteriaceae which was initially identified in Enteroaggregative Escherichia coli strains. This protease exhibits enterotoxin properties, damages the cell cytoskeleton and induces intestinal epithelium alterations, which are associated with a severe inflammatory process. An in-vitro study was conducted to evaluate the effect of Pet on the migration of human peripheral blood monocytes-derived macrophages and its participation in the activation of the early inflammatory response and cytokine expression.

Results

In the macrophage migration activation assay, Pet produced a similar effect to that induced by opsonized zymosan (ZAS). Regarding the cytokine expression, an increase of IL-8, TNF-α (pro-inflammatory) and IL-10 (anti-inflammatory) was identified. In addition to the above results, the nuclear translocation of NF-kB pp65 was also identified. These events are probably related to the inflammatory response identified in the histological examination of intestine rat samples inoculated with Pet during a ligated loop assay.

Conclusion

The results showed that Pet participates as an immunostimulant molecule for macrophages, which activates both their mobility and cytokine expression. These observations suggest that the toxin participates in the inflammatory process that is observed during the host infection by EAEC Pet producing.

Evaluation of Prevalence, Homology and Immunogenicity of Dispersin among Enteroaggregative Escherichia coli Isolates from Iran

Background:

Diarrhea, caused by enteroaggregative Escherichia coli (EAEC), is an important infection leading toillness and death. Numerous virulent factors have been described in EAEC. However, their prevalence was highly variable among EAECs of distinct geographic locations. Studies have shown that dispersin (antiaggregation protein, aap) is one of the important and abundant virulent factors in EAEC. In this study, we aimed to determine the presence, conservation, and immunogenicity of aap gene in EAEC isolated from Iranian patients.

Methods:

PCR amplification of aap gene in the EAEC isolates was performed, and the aap gene was cloned in pBAD-gIIIA vector. The sequence of aap gene was analyzed using the ExPASy and BLAST tools. The expression of aap gene was performed in E. coli Top10, and expression confirmation was carried out by SDS-PAGE and Western-blot techniques. Rabbits were immunized with purified dispersin protein emulsified with Freund’s adjuvant. Sera were collected and examined for antibody response. Finally, invitro efficacy of dispersin and anti-dispersin was evaluated.

Results:

The results of PCR showed the presence of aap gene in all of the EAEC isolates with significant homology. Finally, the significant difference between the levels of IgG response in dispersin-injected rabbits and control group was observed.

Conclusion:

Our results were in accordance with other studies that reported the presence of dispersin in the EAEC isolates with high conservation and immunogenicity. Hence, dispersin could be a promising candidate for any probable prevention against EAEC infections.

Pathotypic and Phylogenetic Study of Diarrheagenic Escherichia coli and Uropathogenic E. coli Using Multiplex Polymerase Chain Reaction

BACKGROUND

Acute diarrheal disease and urinary tract infection are leading causes of childhood morbidity and mortality in the developing world. Diarrheagenic Escherichia coli (DEC) has been identified as a major etiologic agent of diarrhea worldwide, and urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) is one of the most common bacterial infections among human beings. Quick and precise detection of these bacteria help provide more effective intervention and management of infection.

OBJECTIVES

In this study we present a precise and sensitive typing and phylogenetic study of UPEC and DEC using multiplex PCR in order to simplify and improve the intervention and management of diarrheal and UT infections.

MATERIALS AND METHODS

In total, 100 urinary tract infection samples (UTI) and 200 specimens from children with diarrhea, which had been diagnosed with E. coli as the underlying agent by differential diagnosis using MacConkey's agar and biochemical study, were submitted for molecular detection. Pathotyping of E. coli pathotypes causing urinary tract infection and diarrhea were examined using a two set multiplex PCR, targeting six specific genes. Phylogenetic typing was done by targeting three genes, including ChuA, YjaA and TspE4C2.

RESULTS

Overall, 88% of DEC and 54% of UTI isolates were positive for one or more of the six genes encoding virulence factors. Prevalence of the genes encoding virulence factors for DEC were 62%, 25%, 24%, 13%, 7% and 5% for ST (ETEC), LT (ETEC), aggR (EAggEC), daaD (DAEC), invE (EIEC) and eae (EPEC), respectively; whereas, the prevalence rates for the UTI samples were 23%, 14%, 6%, 6% and 4% for aggR (EAggEC), LT (ETEC), daaD (DAEC), invE (EIEC) and ST (ETEC), respectively. No coding virulence factors were detected for eae (EPEC). Group B2 was the most prevalent phylogroup and ST was the most frequently detected pathotype in all phylogroups.

CONCLUSIONS

ETEC and EAggEC were the most detected E. coli among stool and UTI samples, emphasizing the need to dedicate more health care attention to this group. In addition, our phylogenetic study may be helpful in figuring out the infection origin and for epidemiological studies. Nonetheless, more research studies with larger sample sizes are suggested for confirming our results.

Prevalence of Mycobacterium avium subsp. paratuberculosis and Escherichia coli in blood samples from patients with inflammatory bowel disease

Mycobacterium avium subsp. paratuberculosis (MAP) and adherent-invasive Escherichia coli (AIEC) have been implicated as primary triggers in Crohn's disease (CD). In this study, we evaluated the prevalence of MAP and E. coli (EC) DNA in peripheral blood from 202 inflammatory bowel disease (IBD) patients at various disease periods and compared against 24 cirrhotic patients with ascites (CIR) (non-IBD controls) and 29 healthy controls (HC). MAP DNA was detected by IS900-specific nested PCR, EC DNA by malB-specific nested PCR and AIEC identity, in selected samples, by sequencing of fimH gene. CD patients with active disease showed the highest MAP DNA prevalence among IBD patients (68 %). Infliximab treatment resulted in decreased MAP detection. CIR patients had high individual and coinfection rates (75 % MAP, 88 % EC and 67 % MAP and EC), whilst HC controls had lower MAP prevalence (38 %) and EC was undetectable in this control group. EC DNA prevalence in IBD patients was highly associated with CD, and 80 % of EC from the selected samples of CD patients analyzed carried the fimH30 allele, with a mutation strongly associated with AIEC. Our results show that coinfection with MAP and AIEC is common and persistent in CD, although the high MAP and EC detection in CIR patients suggested that colonization is, at least, partially dependent on increased gut permeability. Nevertheless, facilitative mechanisms between a susceptible host and these two potential human pathogens may allow their implication in CD pathogenesis.

Recent advances in adherence and invasion of pathogenic Escherichia coli

PURPOSE OF REVIEW

Colonization of the host epithelia by pathogenic Escherichia coli is influenced by the ability of the bacteria to interact with host surfaces. Because the initial step of an E. coli infection is to adhere, invade, and persist within host cells, some strategies used by intestinal and extraintestinal E. coli to infect host cell are presented.

RECENT FINDINGS

This review highlights recent progress understanding how extraintestinal pathogenic E. coli strains express specific adhesins or invasins that allow colonization of the urinary tract or the meninges, while intestinal E. coli strains are able to colonize different regions of the intestinal tract using other specialized adhesins or invasins. Finally, evaluation of different diets and environmental conditions regulating the colonization of these pathogens is discussed.

SUMMARY

Discovery of new interactions between pathogenic E. coli and the host epithelial cells unravels the need for more mechanistic studies that can provide new clues regarding how to combat these infections.

Adherence and virulence genes of Escherichia coli from children diarrhoea in the Brazilian Amazon

The bacterial pathogen most commonly associated with endemic forms of childhood diarrhoea is Escherichia coli . Studies of epidemiological characteristics of HEp-2 cell-adherent E. coli in diarrhoeal disease are required, particularly in developing countries. The aim of this study was evaluate the presence and significance of adherent Escherichia coli from diarrhoeal disease in children. The prevalence of LA, AA, and DA adherence patterns were determined in HEp-2 cells, the presence of virulence genes and the presence of the O serogroups in samples obtained from 470 children with acute diarrhoea and 407 controls in Porto Velho, Rondônia, Brazil. E. coli isolates were identified by PCR specific for groups of adherent E. coli . Out of 1,156 isolates obtained, 128 (11.0%) were positive for eae genes corresponding to EPEC, however only 38 (29.6%) of these amplified bfpA gene . EAEC were isolated from 164 (14.1%) samples; of those 41(25%), 32 (19%) and 16 (9.7%) amplified eagg , aggA or aafA genes, respectively and aggA was significantly associated with diarrhoea ( P = 0.00006). DAEC identified by their adhesion pattern and there were few isolates. In conclusion, EAEC was the main cause of diarrhoea in children, especially when the aggA gene was present, followed by EPEC and with a negligible presence of DAEC.

Emerging infectious colitis

PURPOSE OF REVIEW

The present review will highlight recent advances in the knowledge of emerging pathogens causing infectious colitis and provide a description of the most important food-borne outbreaks.

RECENT FINDINGS

Outbreaks of enteric disease caused by Salmonella spp., Campylobacter spp., and Shiga toxin-producing Escherichia coli (STEC) continue to surprise with new epidemiological findings or changing virulence characteristics. These pathogens evolve to exploit novel opportunities for spread and transmission, such as fresh produce within the food chain, and generate new public health challenges. Organic sprouts were recently considered as the source responsible for a large German disease outbreak comprising 3842 patients. The outbreak strain was identified as an enteroaggregative STEC O104:H4 (EAggC), a rare hybrid pathogen that harbours the phage encoded Shiga toxin gene and antibiotic resistance in an EAggEC background. Clostridium difficile PCR ribotype 078 is emerging across Europe, causing severe disease outside healthcare facilities as well as disease in farm animals, indicating that the species border has been crossed. Although the global impact of cryptosporidiosis is less pronounced, these organisms have been responsible for large outbreaks of infectious diarrhoea, often not reported. Invasive listeriosis is a serious food-borne illness and was found recently in 28 US states affecting 147 patients, associated with eating contaminated cantaloupe. Outbreaks of gastroenteritis caused by Listeria monocytogenes are most likely severely underestimated. Centralized surveillance of food-borne enteropathogens is essential for the early detection of disease outbreaks and for the organization of an immediate and appropriate response.

SUMMARY

An improved understanding of the pathogenesis, pathology and epidemiology of emerging enteropathogens causing infectious colitis will provide new approaches for disease prevention and control.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Clinical implications of enteroadherent Escherichia coli

Pathogenic Escherichia coli that colonize the small intestine primarily cause gastrointestinal illness in infants and travelers. The main categories of pathogenic E. coli that colonize the epithelial lining of the small intestine are enterotoxigenic E. coli, enteropathogenic E. coli, and enteroaggregative E. coli. These organisms accomplish their pathogenic process by a complex, coordinated multistage strategy, including nonintimate adherence mediated by various adhesins. These so called "enteroadherent E. coli" categories subsequently produce toxins or effector proteins that are either secreted to the milieu or injected to the host cell. Finally, destruction of the intestinal microvilli results from the intimate adherence or the toxic effect exerted over the epithelia, resulting in water secretion and diarrhea. In this review, we summarize the current state of knowledge regarding these enteroadherent E. coli strains and the present clinical understanding of how these organisms colonize the human intestine and cause disease.

Escherichia coli virulence factors

Escherichia coli was described in 1885 by a German pediatrician, Theodor Escherich, in the faeces of a child suffering diarrhoea. In 1893, a Danish veterinarian postulated that the E. coli species comprises different strains, some being pathogens, others not. Today the E. coli species is subdivided into several pathogenic strains causing different intestinal, urinary tract or internal infections and pathologies, in animal species and in humans. Since this congress topic is the interaction between E. coli and the mucosal immune system, the purpose of this manuscript is to present different classes of adhesins (fimbrial adhesins, afimbrial adhesins and outer membrane proteins), the type 3 secretion system, and some toxins (oligopeptide, AB, and RTX pore-forming toxins) produced by E. coli, that can directly interact with the epithelial cells of the intestinal, respiratory and urinary tracts.

In vivo bioluminescence imaging of Escherichia coli O104:H4 and role of aerobactin during colonization of a mouse model of infection

Background

A major outbreak of bloody diarrhea associated with Shiga toxin-producing Escherichia coli O104:H4 occurred early in 2011, to which an unusual number of hemolytic uremic syndrome cases were linked. Due to limited information regarding pathogenesis and/or virulence properties of this particular serotype, we investigated the contribution of the aerobactin iron transport system during in vitro and in vivo conditions.

Results

A bioluminescent reporter construct was used to perform real-time monitoring of E. coli O104:H4 in a mouse model of infection. We verified that our reporter strain maintained characteristics and growth kinetics that were similar to those of the wild-type E. coli strain. We found that the intestinal cecum of ICR (CD-1) mice was colonized by O104:H4, with bacteria persisting for up to 7 days after intragastric inoculation. MALDI-TOF analysis of heat-extracted proteins was performed to identify putative surface-exposed virulence determinants. A protein with a high similarity to the aerobactin iron receptor was identified and further demonstrated to be up-regulated in E. coli O104:H4 when grown on MacConkey agar or during iron-depleted conditions. Because the aerobactin iron acquisition system is a key virulence factor in Enterobacteriaceae, an isogenic aerobactin receptor (iutA) mutant was created and its intestinal fitness assessed in the murine model. We demonstrated that the aerobactin mutant was out-competed by the wild-type E. coli O104:H4 during in vivo competition experiments, and the mutant was unable to persist in the cecum.

Conclusion

Our findings demonstrate that bioluminescent imaging is a useful tool to monitor E. coli O104:H4 colonization properties, and the murine model can become a rapid way to evaluate bacterial factors associated with fitness and/or colonization during E. coli O104:H4 infections.

Analyzing of expression of novel polypeptide complexes consisting of Shiga toxin B subunit and Adherence Fimbriae of Escherichia coli based on in silico modeling

Enterohemorrhagic (EHEC) and enteroaggregative (EAEC) are two pathotypes of diarrheagenic Escherichia coli. EAEC strains express adhesins called aggregate adherence fimbriae (AAFs) which the bacteria use to adhere to intestinal mucosa. EHEC virulence factor is Shiga toxin which belongs to the AB5 toxin family. B subunit, the nontoxic part of Shiga toxin (StxB), forms a homo pentamer and is responsible for binding to target cells. StxB has recently been proven to have adjuvant activity. In the current study we fused StxB encoding gene to 3' end of genes encoding two variants of AAFs, i.e., AAF/I and AAF/II. The in silico studies on tertiary structure and biochemical characteristics of Shiga toxin A subunit (StxA) revealed more resemblance to AAF/II than AAF/I. The constructs were prepared in a way that StxB could imitate its natural structure (pentamer formation) and its position (C-terminus) in the native toxin complex. The expression of these constructs showed the formation of AAF/II-B as a protein complex but with lower molecular mass than its expected size. In contrast, the AAF/I-B complex was not formed. Overall, the results of in silico studies and expression experiments together revealed that despite AAF/II-B expression, StxB failed to form pentamer. Therefore the observed protein complex has lower molecular mass. Since StxB is bound to AAF/II through disulfide bond, this bond prevents pentamer formation of StxB. However, due to the lack of disulfide bond between AAF/I and StxB, no protein complex is formed, thus StxB maintains its pentamer structure.

Adherence of enteroaggregative Escherichia coli to the ileal and colonic mucosa: an in vitro study utilizing the scanning electron microscopy

CONTEXT

Enteroaggregative Escherichia coli strains have been associated with persistent diarrhea in several developing countries. In vivo procedures with animal models, in vitro assays with cellular lines and in vitro organ culture with intestinal fragments have been utilized to study these bacteria and their pathogenicity.

OBJECTIVE

The present experimental research assessed the pathogenic interactions of three enteroaggregative Escherichia coli strains, using the in vitro organ culture, in order to show the adherence to different regions of both, the ileal and the colonic mucosa and demonstrate possible mechanisms that could have the participation in the prolongation of diarrheiogenic process.

METHODS

This study used intestinal fragments from terminal ileum and colon that were excised from pediatric patients undergoing intestinal surgeries and from adult patients that underwent to colonoscopic procedures. Each strain was tested with three intestinal fragments for each region. Tissue was fixed for scanning electron microscopic analysis.

RESULTS

These bacteria colonized ileal and colonic mucosa in the typical stacked-brick configuration in the ileum and colon. In both regions, the strains were seen over a great amount of mucus and sometimes over the intact epithelium. In some regions, there is a probable evidence of effacement of the microvilli. It was possible to see adhered to the intestinal surface, bacteria fimbrial structures that could be responsible for the adherence process.

CONCLUSION

In order to cause diarrhea, enteroaggregative Escherichia coli strains adhere to the intestinal mucosa, create a mucoid biofilm on the small bowel surface that could justify the digestive-absorptive abnormalities and consequently, prolonging the diarrhea.

CTX-M-15-producing enteroaggregative Escherichia coli as cause of travelers' diarrhea

Travelers’ diarrhea is a major public health problem. From patients in whom diarrhea developed after travel to India, 5 enteroaggregative Escherichia coli strains carrying β-lactamase CTX-M-15 were identified; 3 belonged to clonal complex sequence type 38. This β-lactamase contributes to the multidrug resistance of enteroaggregative E. coli, thereby limiting therapeutic alternatives.

O157:H7 and O104:H4 Vero/Shiga toxin-producing Escherichia coli outbreaks: respective role of cattle and humans

An enteroaggregative Verotoxin (Vtx)-producing Escherichia coli strain of serotype O104:H4 has recently been associated with an outbreak of haemolytic-uremic syndrome and bloody diarrhoea in humans mainly in Germany, but also in 14 other European countries, USA and Canada. This O104:H4 E. coli strain has often been described as an enterohaemorrhagic E. coli (EHEC), i.e. a Vtx-producing E. coli with attaching and effacing properties. Although both EHEC and the German O104:H4 E. coli strains indeed produce Vtx, they nevertheless differ in several other virulence traits, as well as in epidemiological characteristics. For instance, the primary sources and vehicles of typical EHEC infections in humans are ruminants, whereas no animal reservoir has been identified for enteroaggregative E. coli (EAggEC). The present article is introduced by a brief overview of the main characteristics of Vtx-producing E. coli and EAggEC. Thereafter, the O104:H4 E. coli outbreak is compared to typical EHEC outbreaks and the virulence factors and host specificity of EHEC and EAggEC are discussed. Finally, a renewed nomenclature of Vtx-producing E. coli is proposed to avoid more confusion in communication during future outbreaks and to replace the acronym EHEC that only refers to a clinical condition.

Pathophysiology of enteroaggregative Escherichia coli infection: an experimental model utilizing transmission electron microscopy

CONTEXT

Enteroaggregative Escherichia coli strains have been associated with persistent diarrhea in several developing countries. In vivo procedures with animal models as rat, rabbit and gnotobiotic piglets intestinal loops, in vitro assays with cellular lines like T84, Caco 2, HT29, HeLa e HEp-2 and in vitro organ culture with intestinal fragments have been applied to study these bacteria and their pathogenicity.

OBJECTIVES

The present experimental research assessed the pathogenic interactions of three enteroaggregative Escherichia coli strains, using the in vitro organ culture, in order to observe and compare alterations in different regions of both, the ileal and the colonic mucosa.

METHODS

This study applied intestinal fragments from terminal ileum and colon that were excised from pediatric and adult patients that underwent colonoscopic procedures. Tissue was fixed for transmission electron microscopic study. Each bacterium was tested with three intestinal fragments for each region.

RESULTS

Enteroaggregative Escherichia coli strains colonized and provoked citotoxic effects in the ileal and colonic mucosa. Total or partial villi destruction, vacuolization of basal cytoplasm of the enterocytes, epithelium detachment, derangement of the structure and epithelial cell extrusion in ileal mucosa could explain the perpetuation of the diarrhea. Bacterial aggregates were seen in intestinal lumen associated with mucus and cellular debris and in the intercellular spaces of the destroyed epithelium, suggesting bacterial invasion that seemed to be secondary to the destruction of the tissue.

CONCLUSIONS

Pathogenesis of persistent diarrhea should include alterations in the small bowel structures where the digestive-absorptive functions take place. In the colonic mucosa the inflammatory lesions could explain the occurrence of colitis.

Escherichia coli enteroagregativa como agente provocador de diarreia persistente: modelo experimental utilizando microscopia óptica de luz

OBJETIVO: Avaliar interações de amostras de Escherichia coli enteroagregativa com tecido intestinal humano, a fim de documentar potenciais alterações em diferentes regiões do trato digestivo. MÉTODOS: Amostras de Escherichia coli enteroagregativa isoladas das fezes de crianças com diarreia persistente e a amostra protótipo 042, isolada de uma criança com diarreia em Lima, no Peru (controle positivo), foram analisadas por microscopia óptica de luz após semeadura em cultura de orgão in vitro de fragmentos de mucosa ileal e colônica. Foram analisadas as interações entre as diferentes cepas de Escherichia coli enteroagregativa e as mucosas ileal e colônica. RESULTADOS: A análise por microscopia óptica de luz indicou associação destes micro-organismos com o epitélio, provocando alterações. As cepas estudadas aderiram a ambas as regiões avaliadas (intestino delgado distal e grosso) e causaram alterações, especialmente naquelas áreas onde interagiram diretamente com o epitélio. No íleo, algumas regiões mostraram internalização secundária. CONCLUSÕES: Esses agentes podem causar diarreia persistente por meio de alterações no intestino delgado, no qual ocorrem as funções digestivo-absortivas. As lesões inflamatórias descritas na mucosa colônica poderiam explicar a colite mostrada em algumas crianças infectadas por Escherichia coli enteroagregativa.

The population dynamics of bacteria in physically structured habitats and the adaptive virtue of random motility

Why is motility so common in bacteria? An obvious answer to this ecological and evolutionary question is that in almost all habitats, bacteria need to go someplace and particularly in the direction of food. Although the machinery required for motility and chemotaxis (acquiring and processing the information needed to direct movement toward nutrients) are functionally coupled in contemporary bacteria, they are coded for by different sets of genes. Moreover, information that resources are more abundant elsewhere in a habitat would be of no value to a bacterium unless it already had the means to get there. Thus, motility must have evolved before chemotaxis, and bacteria with flagella and other machinery for propulsion in random directions must have an advantage over bacteria relegated to moving at the whim of external forces alone. However, what are the selection pressures responsible for the evolution and maintenance of undirected motility in bacteria? Here we use a combination of mathematical modeling and experiments with Escherichia coli to generate and test a parsimonious and ecologically general hypothesis for the existence of undirected motility in bacteria: it enables bacteria to move away from each other and thereby obtain greater individual shares of resources in physically structured environments. The results of our experiments not only support this hypothesis, but are quantitatively and qualitatively consistent with the predictions of our model.

Complete genome sequence of adherent invasive Escherichia coli UM146 isolated from Ileal Crohn's disease biopsy tissue

Escherichia coli UM146 was isolated from the ileum of a Crohn's disease patient. It adheres to and invades enterocytes and can replicate inside macrophages. Its complete genome sequence reveals that it is most closely related to the human urinary tract pathogen E. coli CFT073, but it has a host of genes that are novel and to which no function has been ascribed.