Contributions of O island 48 to adherence of enterohemorrhagic Escherichia coli O157:H7 to epithelial cells in vitro and in ligated pig ileal loops

The tellurite resistance gene cluster of pathogenic bacteria and its effect on oxidative stress response

Tellurite resistance gene clusters have been identified in numerous pathogenic bacteria, including clinical isolates of Escherichia coli. The rareness of tellurium in host organisms and the noncontaminated environment raises a question about the true functionality of tellurite resistance gene clusters in pathogenesis and their possible contribution to bacterial fitness. The study aims to point out the beneficial effects of the tellurite resistance gene cluster of pathogenic bacteria to survive in ROS-rich environments. Here, we analysed the bacterial response to oxidative stress conditions with and without tellurite resistance gene clusters, which are composed of terWY1XY2Y3 and terZABCDEF genes. By measuring the levels of protein carbonylation, lipid peroxidation, and expression changes of oxidative stress genes upon oxidative stress, we propose a tellurite resistance gene cluster contribution to the elimination of oxidative damage, potentially increasing fitness and resistance to reactive oxygen species during macrophage attack. We have shown a different beneficial effect of various truncated versions of the tellurite resistance gene cluster on cell survival. The terBCDEF genes increased the survival of E. coli strain MC4100 by 13.21%, terW and terZABCDEF by 10.09%, and terWY1XY2Y3 and terZABCDEF by 25.57%, respectively. The ability to survive tellurite treatment is the most significant at 44.8% in wild clinical strain KL53 compared to laboratory strain E. coli MC4100 due to a complete wild-type plasmid presence.

Virulence-related O islands in enterohemorrhagic Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a principally foodborne pathogen linked to serious diseases, including bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. Comparative genomics analysis revealed that EHEC O157 contains 177 unique genomic islands, termed O islands, compared with the nonpathogenic E. coli K-12 laboratory strain. These O islands contribute largely to the pathogenicity of EHEC O157:H7 by providing numerous virulence factors, effectors, virulence regulatory proteins, and virulence regulatory sRNAs. The present review aimed to provide a comprehensive understanding of the research progress on the function of O islands, especially focusing on virulence-related O islands.

Characterization of the Tellurite-Resistance Properties and Identification of the Core Function Genes for Tellurite Resistance in Pseudomonas citronellolis SJTE-3

Tellurite is highly toxic to bacteria and commonly used in the clinical screening for pathogens; it is speculated that there is a potential relationship between tellurite resistance and bacterial pathogenicity. Until now, the core function genes of tellurite resistance and their characteristics are still obscure. Pseudomonas citronellolis SJTE-3 was found able to resist high concentrations of tellurite (250 μg/mL) and formed vacuole-like tellurium nanostructures. The terZABCDE gene cluster located in the large plasmid pRBL16 endowed strain SJTE-3 with the tellurite resistance of high levels. Although the terC and terD genes were identified as the core function genes for tellurite reduction and resistance, the inhibition of cell growth was observed when they were used solely. Interestingly, co-expression of the terA gene or terZ gene could relieve the burden caused by the expression of the terCD genes and recover normal cell growth. TerC and TerD proteins commonly shared the conserved sequences and are widely distributed in many pathogenic bacteria, highly associated with the pathogenicity factors.

Diversity of the Tellurite Resistance Gene Operon in Escherichia coli

Tellurite is highly toxic to most bacteria owing to its strong oxidative ability. However, some bacteria demonstrate tellurite resistance. In particular, some Escherichia coli strains, including Shiga toxin-producing E. coli O157:H7, are known to be resistant to tellurite. This resistance is involved in ter operon, which is usually located on a prophage-like element of the chromosome. The characteristics of the ter operon have been investigated mainly by genome analysis of pathogenic E. coli; however, the distribution and structural characteristics of the ter operon in other E. coli are almost unknown. To clarify these points, we examined 106 E. coli strains carrying the ter operon from various animals. The draft genomes of 34 representative strains revealed that ter operons were clearly classified into four subtypes, ter-type 1–4, at the nucleotide sequence level. Complete genomic sequences revealed that operons belonging to three ter-types (1, 3, and 4) were located on the prophage-like elements on the chromosome, whereas the ter-type 2 operon was located on the IncHI2 plasmid. The positions of the tRNA^Ser, tRNA^Met, and tRNA^Phe indicated the insertion sites of elements carrying the ter operons. Using the PCR method developed in this study, 106 strains were classified as type 1 (n = 66), 2 (n = 13), 3 (n = 8), and 4 (n = 17), and two strains carried both types 1 and 2. Furthermore, significant differences in the minimum inhibitory concentration (MIC) of tellurite were observed between strains carrying ter-type 4 and the others (p < 0.05). The ter-type was also closely related to the isolation source, with types 2 and 4 associated with chickens and deer, respectively. This study provided new insights related not only to genetic characteristics of the ter operons, but also to phenotypic and ecological characteristics that may be related to the diversity of the operon.

Molecular determinants of surface colonisation in diarrhoeagenic Escherichia coli (DEC): from bacterial adhesion to biofilm formation

Escherichia coli is primarily known as a commensal colonising the gastrointestinal tract of infants very early in life but some strains being responsible for diarrhoea, which can be especially severe in young children. Intestinal pathogenic E. coli include six pathotypes of diarrhoeagenic E. coli (DEC), namely, the (i) enterotoxigenic E. coli, (ii) enteroaggregative E. coli, (iii) enteropathogenic E. coli, (iv) enterohemorragic E. coli, (v) enteroinvasive E. coli and (vi) diffusely adherent E. coli. Prior to human infection, DEC can be found in natural environments, animal reservoirs, food processing environments and contaminated food matrices. From an ecophysiological point of view, DEC thus deal with very different biotopes and biocoenoses all along the food chain. In this context, this review focuses on the wide range of surface molecular determinants acting as surface colonisation factors (SCFs) in DEC. In the first instance, SCFs can be broadly discriminated into (i) extracellular polysaccharides, (ii) extracellular DNA and (iii) surface proteins. Surface proteins constitute the most diverse group of SCFs broadly discriminated into (i) monomeric SCFs, such as autotransporter (AT) adhesins, inverted ATs, heat-resistant agglutinins or some moonlighting proteins, (ii) oligomeric SCFs, namely, the trimeric ATs and (iii) supramolecular SCFs, including flagella and numerous pili, e.g. the injectisome, type 4 pili, curli chaperone-usher pili or conjugative pili. This review also details the gene regulatory network of these numerous SCFs at the various stages as it occurs from pre-transcriptional to post-translocational levels, which remains to be fully elucidated in many cases.

Magnesium Sensing Regulates Intestinal Colonization of Enterohemorrhagic Escherichia coli O157:H7

Sensing specific gut metabolites is an important strategy for inducing crucial virulence programs by enterohemorrhagic Escherichia coli (EHEC) O157:H7 during colonization and infection. Here, we identified a virulence-regulating pathway wherein the PhoQ/PhoP two-component regulatory system signals to the O island 119-encoded low magnesium-induced regulator A (LmiA), which, in turn, activates locus of enterocyte effacement (LEE) genes to promote EHEC O157:H7 adherence in the low-magnesium conditions of the large intestine. This regulatory pathway is widely present in a range of EHEC and enteropathogenic E. coli (EPEC) serotypes. Disruption of this pathway significantly decreased EHEC O157:H7 adherence in the mouse intestinal tract. Moreover, mice fed a magnesium-rich diet showed significantly reduced EHEC O157:H7 adherence in vivo, indicating that magnesium may help in preventing EHEC and EPEC infection in humans.

The large intestinal pathogen enterohemorrhagic Escherichia coli (EHEC) O157:H7 detects host cues to regulate virulence gene expression during colonization and infection. However, virulence regulatory mechanisms of EHEC O157:H7 in the human large intestine are not fully understood. Herein, we identified a virulence-regulating pathway where the PhoQ/PhoP two-component regulatory system senses low magnesium levels and signals to the O island 119-encoded Z4267 (LmiA; low magnesium-induced regulator A), directly activating loci of enterocyte effacement genes to promote EHEC O157:H7 adherence in the large intestine. Disruption of this pathway significantly decreased EHEC O157:H7 adherence in the mouse intestinal tract. Moreover, feeding mice a magnesium-rich diet significantly reduced EHEC O157:H7 adherence in vivo. This LmiA-mediated virulence regulatory pathway is also conserved among several EHEC and enteropathogenic E. coli serotypes; therefore, our findings support the use of magnesium as a dietary supplement and provide greater insights into the dietary cues that can prevent enteric infections.

Pathogenicity Factors of Genomic Islands in Intestinal and Extraintestinal Escherichia coli

Escherichia coli is a versatile bacterial species that includes both harmless commensal strains and pathogenic strains found in the gastrointestinal tract in humans and warm-blooded animals. The growing amount of DNA sequence information generated in the era of "genomics" has helped to increase our understanding of the factors and mechanisms involved in the diversification of this bacterial species. The pathogenic side of E. coli that is afforded through horizontal transfers of genes encoding virulence factors enables this bacterium to become a highly diverse and adapted pathogen that is responsible for intestinal or extraintestinal diseases in humans and animals. Many of the accessory genes acquired by horizontal transfers form syntenic blocks and are recognized as genomic islands (GIs). These genomic regions contribute to the rapid evolution, diversification and adaptation of E. coli variants because they are frequently subject to rearrangements, excision and transfer, as well as to further acquisition of additional DNA. Here, we review a subgroup of GIs from E. coli termed pathogenicity islands (PAIs), a concept defined in the late 1980s by Jörg Hacker and colleagues in Werner Goebel's group at the University of Würzburg, Würzburg, Germany. As with other GIs, the PAIs comprise large genomic regions that differ from the rest of the genome by their G + C content, by their typical insertion within transfer RNA genes, and by their harboring of direct repeats (at their ends), integrase determinants, or other mobility loci. The hallmark of PAIs is their contribution to the emergence of virulent bacteria and to the development of intestinal and extraintestinal diseases. This review summarizes the current knowledge on the structure and functional features of PAIs, on PAI-encoded E. coli pathogenicity factors and on the role of PAIs in host-pathogen interactions.

Transcriptional Activator OvrA Encoded in O Island 19 Modulates Virulence Gene Expression in Enterohemorrhagic Escherichia coli O157:H7

The human intestinal pathogen enterohemorrhagic Escherichia coli (EHEC) O157:H7 causes bloody diarrhea, hemorrhagic colitis, and fatal hemolytic uremic syndrome. Its genome contains 177 unique O islands (OIs), which contribute largely to the high virulence and pathogenicity although most OI genes remain uncharacterized. In the current study, we demonstrated that OI-19 is required for EHEC O157:H7 adherence to host cells. Z0442 (OI-encoded virulence regulator A [OvrA]) encoded in OI-19 positively regulated bacterial adherence by activating locus of enterocyte effacement (LEE) gene expression through direct OvrA binding to the gene promoter region of the LEE gene master regulator Ler. Mouse colonization experiments revealed that OvrA promotes EHEC O157:H7 adherence in mouse intestine, preferentially the colon. Finally, OvrA also regulated virulence in other non-O157 pathogenic E. coli, including EHEC strains O145:H28 and O157:H16 and enteropathogenic E. coli strain O55:H7. Our work markedly enriches the understanding of bacterial adherence control and provides another example of laterally acquired regulators that mediate LEE gene expression.

Identification and detection of iha subtypes in LEE-negative Shiga toxin-producing Escherichia coli (STEC) strains isolated from humans, cattle and food

LEE-negative Shiga toxin-producing Escherichia coli (STEC) strains are important cause of infection in humans and they should be included in the public health surveillance systems. Some isolates have been associated with haemolytic uremic syndrome (HUS) but the mechanisms of pathogenicity are is a field continuos broadening of knowledge. The IrgA homologue adhesin (Iha), encoded by iha, is an adherence-conferring protein and also a siderophore receptor distributed among LEE-negative STEC strains. This study reports the presence of different subtypes of iha in LEE-negative STEC strains. We used genomic analyses to design PCR assays for detecting each of the different iha subtypes and also, all the subtypes simultaneously. LEE-negative STEC strains were designed and different localizations of this gene in STEC subgroups were examinated.

Genomic analysis detected iha in a high percentage of LEE-negative STEC strains. These strains generally carried iha sequences similar to those harbored by the Locus of Adhesion and Autoaggregation (LAA) or by the plasmid pO113. Besides, almost half of the strains carried both subtypes. Similar results were observed by PCR, detecting iha LAA in 87% of the strains (117/135) and iha pO113 in 32% of strains (43/135). Thus, we designed PCR assays that allow rapid detection of iha subtypes harbored by LEE-negative strains. These results highlight the need to investigate the individual and orchestrated role of virulence genes that determine the STEC capacity of causing serious disease, which would allow for identification of target candidates to develop therapies against HUS.

LysR-type transcriptional regulator OvrB encoded in O island 9 drives enterohemorrhagic Escherichia coli O157:H7 virulence

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 (O157) is a major foodborne pathogen that causes severe illness in humans worldwide. The genome of O157 contains 177 genomic islands known as O islands (OIs), including Shiga toxin-converting phages (OI-45 and OI-93) and the locus for enterocyte effacement (LEE) pathogenicity island (OI-148). However, most genes in OIs are uncharacterized and code for unknown functions. In this study, we demonstrated, for the first time, that OI-9 encodes a novel transcriptional activator, Z0346 (named OvrB), which is required for bacterial adherence to host cells and LEE gene expression in O157. OvrB directly binds to the promoter region of LEE1 and activates the transcription of ler (encoding a master regulator of LEE genes), which in turn activates LEE1–5 genes to promote O157 adherence. Furthermore, mouse oral infection assays showed that OvrB promotes O157 colonization in the mouse intestine. Finally, OvrB is shown to be a widespread transcriptional activator of virulence genes in other enterohemorrhagic and enteropathogenic Escherichia coli serotypes. Our work significantly expands the understanding of bacterial virulence control and provides new evidence suggesting that horizontally transferred regulator genes mediate LEE gene expression.

Molecular profiling and antimicrobial resistance of Shiga toxin-producing Escherichia coli O26, O45, O103, O121, O145 and O157 isolates from cattle on cow-calf operations in South Africa

In this study, 140 cattle STEC isolates belonging to serogroups O157, O26, O145, O121, O103 and O45 were characterized for 38 virulence-associated genes, antimicrobial resistance profiles and genotyped by PFGE. The majority of isolates carried both stx1 and stx2 concurrently, stx2c, and stx2d; plasmid-encoded genes ehxA, espP, subA and saa but lacked katP and etpD and eaeA. Possession of eaeA was significantly associated with the presence of nle genes, katP, etpD, ureC and terC. However, saa and subA, stx1c and stx1d were only detected in eaeA negative isolates. A complete OI-122 and most non-LEE effector genes were detected in only two eaeA positive serotypes, including STEC O157:H7 and O103:H2. The eaeA gene was detected in STEC serotypes that are commonly implicated in severe humans disease and outbreaks including STEC O157:H7, STEC O145:H28 and O103:H2. PFGE revealed that the isolates were highly diverse with very low rates of antimicrobial resistance. In conclusion, only a small number of cattle STEC serotypes that possessed eaeA, had the highest number of virulence-associated genes, indicative of their high virulence. Further characterization of STEC O157:H7, STEC O145:H28 and O103:H2 using whole genome sequencing will be needed to fully understand their virulence potential for humans.

The Prophages of Citrobacter rodentium Represent a Conserved Family of Horizontally Acquired Mobile Genetic Elements Associated with Enteric Evolution towards Pathogenicity

Prophage-mediated horizontal gene transfer (HGT) plays a key role in the evolution of bacteria, enabling access to new environmental niches, including pathogenicity. Citrobacter rodentium is a host-adapted intestinal mouse pathogen and important model organism for attaching and effacing (A/E) pathogens, including the clinically significant enterohaemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC, respectively). Even though C. rodentium contains 10 prophage genomic regions, including an active temperate phage, ΦNP, little was known regarding the nature of C. rodentium prophages in the bacterium's evolution toward pathogenicity. In this study, our characterization of ΦNP led to the discovery of a second, fully functional temperate phage, named ΦSM. We identify the bacterial host receptor for both phages as lipopolysaccharide (LPS). ΦNP and ΦSM are likely important mediators of HGT in C. rodentium Bioinformatic analysis of the 10 prophage regions reveals cargo genes encoding known virulence factors, including several type III secretion system (T3SS) effectors. C. rodentium prophages are conserved across a wide range of pathogenic enteric bacteria, including EPEC and EHEC as well as pathogenic strains of Salmonella enterica, Shigella boydii, and Klebsiella pneumoniae Phylogenetic analysis of core enteric backbone genes compared against prophage evolutionary models suggests that these prophages represent an important, conserved family of horizontally acquired enteric-bacterium-associated pathogenicity determinants. In addition to highlighting the transformative role of bacteriophage-mediated HGT in C. rodentium's evolution toward pathogenicity, these data suggest that the examination of conserved families of prophages in other pathogenic bacteria and disease outbreaks might provide deeper evolutionary and pathological insights otherwise obscured by more classical analysis.IMPORTANCE Bacteriophages are obligate intracellular parasites of bacteria. Some bacteriophages can confer novel bacterial phenotypes, including pathogenicity, through horizontal gene transfer (HGT). The pathogenic bacterium Citrobacter rodentium infects mice using mechanisms similar to those employed by human gastrointestinal pathogens, making it an important model organism. Here, we examined the 10 prophages of C. rodentium, investigating their roles in its evolution toward virulence. We characterized ΦNP and ΦSM, two endogenous active temperate bacteriophages likely important for HGT. We showed that the 10 prophages encode predicted virulence factors and are conserved within other intestinal pathogens. Phylogenetic analysis suggested that they represent a conserved family of horizontally acquired enteric-bacterium-associated pathogenic determinants. Consequently, similar analysis of prophage elements in other pathogens might further understanding of their evolution and pathology.

Quantification of enterohemorrhagic Escherichia coli O157:H7 protein abundance by high-throughput proteome

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a human pathogen responsible for diarrhea, hemorrhagic colitis and hemolytic uremic syndrome (HUS). To promote a comprehensive insight into the molecular basis of EHEC O157:H7 physiology and pathogenesis, the combined proteome of EHEC O157:H7 strains, Clade 8 and Clade 6 isolated from cattle in Argentina, and the standard EDL933 (clade 3) strain has been analyzed. From shotgun proteomic analysis a total of 2,644 non-redundant proteins of EHEC O157:H7 were identified, which correspond approximately 47% of the predicted proteome of this pathogen. Normalized spectrum abundance factor analysis was performed to estimate the protein abundance. According this analysis, 50 proteins were detected as the most abundant of EHEC O157:H7 proteome. COG analysis showed that the majority of the most abundant proteins are associated with translation processes. A KEGG enrichment analysis revealed that Glycolysis / Gluconeogenesis was the most significant pathway. On the other hand, the less abundant detected proteins are those related to DNA processes, cell respiration and prophage. Among the proteins that composed the Type III Secretion System, the most abundant protein was EspA. Altogether, the results show a subset of important proteins that contribute to physiology and pathogenicity of EHEC O157:H7.

Adherence factors of enterohemorrhagic Escherichia coli O157:H7 strain Sakai influence its uptake into the roots of Valerianella locusta grown in soil

Increasing numbers of outbreaks caused by enterohemorrhagic Escherichia coli (EHEC) are associated with the consumption of contaminated fresh produce. The contamination of the plants may occur directly on the field via irrigation water, surface water, manure or fecal contamination. Suggesting a low infectious dose of 10 to 102 cells, internalization of EHEC into plant tissue presents a serious public health threat. Therefore, the ability of EHEC O157:H7 strain Sakai to adhere to and internalize into root tissues of the lamb's lettuce Valerianella locusta was investigated under the environmental conditions of a greenhouse. Moreover, the influence of the two adherence and colonization associated genes hcpA and iha was surveyed regarding their role for attachment and invasion. Upon soil contamination, the number of root-internalized cells of EHEC O157:H7 strain Sakai exceeded 102 cfu/g roots. Deletion of one or both of the adherence factor genes did not alter the overall attachment of EHEC O157:H7 strain Sakai to the roots, but significantly reduced the numbers of internalized bacteria by a factor of between 10 and 30, indicating their importance for invasion of EHEC O157:H7 strain Sakai into plant roots. This study identified intrinsic bacterial factors that play a crucial role during the internalization of EHEC O157:H7 strain Sakai into the roots of Valerianella locusta grown under the growth conditions in a greenhouse.

Transcriptional Activator GmrA, Encoded in Genomic Island OI-29, Controls the Motility of Enterohemorrhagic Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli O157:H7 is a major human enteric pathogen capable of causing large outbreaks of severe infections that induce bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. Its genome contains 177 unique O islands (OIs) including those carrying the main virulence elements, Shiga toxin-converting phages (OI-45 and OI-93) and locus for enterocyte effacement (OI-148). However, many of these islands harbor only genes of unknown function. Here, we demonstrate that OI-29 encodes a newly discovered transcriptional activator, Z0639 (named GmrA), that is required for motility and flagellar synthesis in O157:H7. GmrA directly binds to the promoter of fliA, an RNA polymerase sigma factor, and thereby regulates flagellar genes controlled by FliA. Expression of gmrA is maximal under host conditions (37°C, neutral pH, and physiological osmolarity), and in the presence of host epithelial cells, indicative of a role of this gene in infection by promoting motility. Finally, GmrA was found to be a widespread regulator of bacterial motility and flagellar synthesis in different pathotypes of E. coli. Our work largely enriches our understanding of bacterial motility control, and provides another example of regulators acquired laterally that mediate flagellar synthesis.

Adhesion and invasion to epithelial cells and motility of extended-spectrum β-lactamase-producing Escherichia coli reveal ST131 superiority: a comparative in vitro study of extraintestinal pathogenic E. coli lineages

PURPOSE

Extended-spectrum β-lactamase (ESBL)-producing extraintestinal pathogenic Escherichia coli (ExPEC) sequence type ST131 is pandemic, and it is the major contributor to antibiotic resistance in E. coli. Despite its epidemiological superiority, the physiological reasons that decipher its success remain elusive. We aimed to compare the adhesion, invasion and motility potential of ST131 versus other E. coli lineages.

METHODOLOGY

In this in vitro comparative study, 14 ESBL-producing ExPEC community-onset bacteremia isolates were chosen from a reported clinical collection (Karfunkel D, Carmeli Y, Chmelnitsky I, Kotlovsky T, Navon-Venezia S. Eur J Clin Microbiol Infect Dis 2013;32:513-521). Isolates were divided into two groups, ST131 (n=7) and 'non-ST131', sporadic sequence types (STs) (n=7). Virulence and adhesion genes were screened by PCR in all isolates. Virotyping and serotyping were performed for ST131 isolates. Adhesion and invasion to Caco-2 epithelial cells, and motility on semi-solid agar were quantified and compared between the two groups. Fluorescence microscopy using anti-LPS E. coli antibodies was used for visualization and confirmation of adhesion and invasion.

RESULTS

ST131 isolates belonged to the O25b:H4-B2 subclone. Two ST131 virotypes were found, A (two blaCTX-M-15 H30-Rx) and C (two blaCTX-M-15 H30-Rx and three blaCTX-M-14 H30 isolates). The average number of adhesion and virulence genes carried by ExPEC ST131 isolates and non-ST131 isolates was 5.3 and 3.7, respectively (P<0.05). Group analysis showed that ST131 surpassed non-ST131 lineages in all three physiological properties: adherence (17.1 vs 13.1 %, P<0.001), invasion (0.4 vs 0.17 %, P<0.01), and swarming motility on all media tested (P<0.05).

CONCLUSION

This study demonstrates ST131 superiority that may explain its improved gut-colonization and dissemination capabilities within the host. These insights are an important step in our understanding of ST131 epidemiological success.

CRIP1, a novel immune-related protein, activated by Enterococcus faecalis in porcine gastrointestinal epithelial cells

Cysteine-rich intestinal protein 1 (CRIP1) is an important transcriptional regulation factor during the tumor development. Although it was largely studied in the human or mouse, no report has provided functional evidence for it in the swine. To date, the real sequence of porcine CRIP1 (poCRIP1) was also still unknown. In this study, clear characteristics for the poCRIP1 were represented. A 552bp poCRIP1 cDNA was obtained from porcine brain tissue using real time reverse transcriptase PCR. The poCRIP1 showed 89% and 93% homologous with human and cattle, respectively. And it also contained one conserved domain, LIM-CRIP domain. Meanwhile, the genomic structure and promoter map was done and several conserved transcriptional regulatory sites were also predicted in this study. The expression pattern of poCRIP1 indicated that poCRIP1 is expressed in mucosal tissue. An infection experiment about the gut was designed to analyze whether or not poCRIP1 was functional in gut immunity, and an interesting result was that poCRIP1 was only activated by an opportunistic pathogen, Enterococcus faecalis FA2-2. It was the first report to identify the full-length sequence of poCRIP1 gene, represent a clear characteristic and immunologic role of CRIP1 in domestic animal until now.

Corynebacterium diphtheriae putative tellurite-resistance protein (CDCE8392_0813) contributes to the intracellular survival in human epithelial cells and lethality of Caenorhabditis elegans

Corynebacterium diphtheriae, the aetiologic agent of diphtheria, also represents a global medical challenge because of the existence of invasive strains as causative agents of systemic infections. Although tellurite (TeO3^2-) is toxic to most microorganisms, TeO3^2--resistant bacteria, including C. diphtheriae, exist in nature. The presence of TeO3^2--resistance (Te^R) determinants in pathogenic bacteria might provide selective advantages in the natural environment. In the present study, we investigated the role of the putative Te^R determinant (CDCE8392_813gene) in the virulence attributes of diphtheria bacilli. The disruption of CDCE8392_0813 gene expression in the LDCIC-L1 mutant increased susceptibility to TeO3^2- and reactive oxygen species (hydrogen peroxide), but not to other antimicrobial agents. The LDCIC-L1 mutant also showed a decrease in both the lethality of Caenorhabditis elegans and the survival inside of human epithelial cells compared to wild-type strain. Conversely, the haemagglutinating activity and adherence to and formation of biofilms on different abiotic surfaces were not regulated through the CDCE8392_0813 gene. In conclusion, the CDCE8392_813 gene contributes to the Te^R and pathogenic potential of C. diphtheriae.

Molecular hazard identification of non-O157 Shiga toxin-producing Escherichia coli (STEC)

The complexity regarding Shiga toxin-producing Escherichia coli (STEC) in food safety enforcement as well as clinical care primarily relates to the current inability of an accurate risk assessment of individual strains due to the large variety in serotype and genetic content associated with (severe) disease. In order to classify the clinical and/or epidemic potential of a STEC isolate at an early stage it is crucial to identify virulence characteristics of putative pathogens from genomic information, which is referred to as 'predictive hazard identification'. This study aimed at identifying associations between virulence factors, phylogenetic groups, isolation sources and seropathotypes. Most non-O157 STEC in the Netherlands belong to phylogroup B1 and are characterized by the presence of ehxA, iha and stx2, but absence of eae. The large variability in the number of virulence factors present among serogroups and seropathotypes demonstrated that this was merely indicative for the virulence potential. While all the virulence gene associations have been worked out, it appeared that there is no specific pattern that would unambiguously enable hazard identification for an STEC strain. However, the strong correlations between virulence factors indicate that these arrays are not a random collection but are rather specific sets. Especially the presence of eae was strongly correlated to the presence of many of the other virulence genes, including all non-LEE encoded effectors. Different stx-subtypes were associated with different virulence profiles. The factors ehxA and ureC were significantly associated with HUS-associated strains (HAS) and not correlated to the presence of eae. This indicates their candidacy as important pathogenicity markers next to eae and stx2a.

EHEC Adhesins

Adhesins are a group of proteins in enterohemorrhagic Escherichia coli (EHEC) that are involved in the attachment or colonization of this pathogen to abiotic (plastic or steel) and biological surfaces, such as those found in bovine and human intestines. This review provides the most up-to-date information on these essential adhesion factors, summarizing important historical discoveries and analyzing the current and future state of this research. In doing so, the proteins intimin and Tir are discussed in depth, especially regarding their role in the development of attaching and effacing lesions and in EHEC virulence. Further, a series of fimbrial proteins (Lpf1, Lpf2, curli, ECP, F9, ELF, Sfp, HCP, and type 1 fimbriae) are also described, emphasizing their various contributions to adherence and colonization of different surfaces and their potential use as genetic markers in detection and classification of different EHEC serotypes. This review also discusses the role of several autotransporter proteins (EhaA-D, EspP, Saa and Sab, and Cah), as well as other proteins associated with adherence, such as flagella, EibG, Iha, and OmpA. While these proteins have all been studied to varying degrees, all of the adhesins summarized in this chapter have been linked to different stages of the EHEC life cycle, making them good targets for the development of more effective diagnostics and therapeutics.

Emerging types of Shiga toxin-producing E. coli (STEC) O178 present in cattle, deer, and humans from Argentina and Germany

More than 400 serotypes of Shiga toxin-producing Escherichia coli (STEC) have been implicated in outbreaks and sporadic human diseases. In recent years STEC strains belonging to serogroup O178 have been commonly isolated from cattle and food of bovine origin in South America and Europe. In order to explore the significance of these STEC strains as potential human pathogens, 74 German and Argentinean E. coli O178 strains from animals, food and humans were characterized phenotypically and investigated for their serotypes, stx-genotypes and 43 virulence-associated markers by a real-time PCR-microarray. The majority (n = 66) of the O178 strains belonged to serotype O178:H19. The remaining strains divided into O178:H7 (n = 6), O178:H10 (n = 1), and O178:H16 (n = 1). STEC O178:H19 strains were mainly isolated from cattle and food of bovine origin, but one strain was from a patient with hemolytic uremic syndrome (HUS). Genotyping of the STEC O178:H19 strains by pulsed-field gel electrophoresis revealed two major clusters of genetically highly related strains which differ in their stx-genotypes and non-Stx putative virulence traits, including adhesins, toxins, and serine-proteases. Cluster A-strains including the HUS-strain (n = 35) carried genes associated with severe disease in humans (stx2a, stx2d, ehxA, saa, subAB1, lpfAO113 , terE combined with stx1a, espP, iha). Cluster B-strains (n = 26) showed a limited repertoire of virulence genes (stx2c, pagC, lpfAO113 , espP, iha). Among O178:H7 strains isolated from deer meat and patients with uncomplicated disease a new STEC variant was detected that is associated with the genotype stx1c/stx2b/ehxA/subAB2/espI/[terE]/espP/iha. None of the STEC O178 strains was positive for locus of enterocyte effacement (LEE)- and nle-genes. Results indicate that STEC O178:H19 strains belong to the growing group of LEE-negative STEC that should be considered with respect to their potential to cause diseases in humans.

Construction and characterization of tetH overexpression and knockout strains of Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is a major participant in consortia of microorganisms used for bioleaching. It can obtain energy from the oxidation of Fe(2+), H2, S(0), and various reduced inorganic sulfur compounds (RISCs). Tetrathionate is a key intermediate during RISC oxidation, hydrolyzed by tetrathionate hydrolase (TetH), and used as sole energy source. In this study, a tetH knockout (ΔtetH) mutant and a tetH overexpression strain were constructed and characterized. The tetH overexpression strain grew better on sulfur and tetrathionate and possessed a higher rate of tetrathionate utilization and TetH activity than the wild type. However, its cell yields on tetrathionate were much lower than those on sulfur. The ΔtetH mutant could not grow on tetrathionate but could proliferate on sulfur with a lower cell yield than the wild type's, which indicated that tetrathionate hydrolysis is mediated only by TetH, encoded by tetH. The ΔtetH mutant could survive in ferrous medium with an Fe(2+) oxidation rate similar to that of the wild type. For the tetH overexpression strain, the rate was relatively higher than that of the wild type. The reverse transcription-quantitative PCR (qRT-PCR) results showed that tetH and doxD2 acted synergistically, and doxD2 was considered important in thiosulfate metabolism. Of the two sqr genes, AFE_0267 seemed to play as important a role in sulfide oxidation as AFE_1792. This study not only provides a substantial basis for studying the function of the tetH gene but also may serve as a model to clarify other candidate genes involved in sulfur oxidation in this organism.

Lineage-specific distribution of insertion sequence excision enhancer in enterotoxigenic Escherichia coli isolated from swine

Insertion sequences (ISs) are the simplest transposable elements and are widely distributed in bacteria; however, they also play important roles in genome evolution. We recently identified a protein called IS excision enhancer (IEE) in enterohemorrhagic Escherichia coli (EHEC) O157. IEE promotes the excision of IS elements belonging to the IS3 family, such as IS629, as well as several other families. IEE-mediated IS excision generates various genomic deletions that lead to the diversification of the bacterial genome. IEE has been found in a broad range of bacterial species; however, among sequenced E. coli strains, IEE is primarily found in EHEC isolates. In this study, we investigated non-EHEC pathogenic E. coli strains isolated from domestic animals and found that IEE is distributed in specific lineages of enterotoxigenic E. coli (ETEC) strains of serotypes O139 or O149 isolated from swine. The iee gene is located within integrative elements that are similar to SpLE1 of EHEC O157. All iee-positive ETEC lineages also contained multiple copies of IS629, a preferred substrate of IEE, and their genomic locations varied significantly between strains, as observed in O157. These data suggest that IEE may have been transferred among EHEC and ETEC in swine via SpLE1 or SpLE1-like integrative elements. In addition, IS629 is actively moving in the ETEC O139 and O149 genomes and, as in EHEC O157, is promoting the diversification of these genomes in combination with IEE.

Iron, copper, zinc, and manganese transport and regulation in pathogenic Enterobacteria: correlations between strains, site of infection and the relative importance of the different metal transport systems for virulence

For all microorganisms, acquisition of metal ions is essential for survival in the environment or in their infected host. Metal ions are required in many biological processes as components of metalloproteins and serve as cofactors or structural elements for enzymes. However, it is critical for bacteria to ensure that metal uptake and availability is in accordance with physiological needs, as an imbalance in bacterial metal homeostasis is deleterious. Indeed, host defense strategies against infection either consist of metal starvation by sequestration or toxicity by the highly concentrated release of metals. To overcome these host strategies, bacteria employ a variety of metal uptake and export systems and finely regulate metal homeostasis by numerous transcriptional regulators, allowing them to adapt to changing environmental conditions. As a consequence, iron, zinc, manganese, and copper uptake systems significantly contribute to the virulence of many pathogenic bacteria. However, during the course of our experiments on the role of iron and manganese transporters in extraintestinal Escherichia coli (ExPEC) virulence, we observed that depending on the strain tested, the importance of tested systems in virulence may be different. This could be due to the different set of systems present in these strains, but literature also suggests that as each pathogen must adapt to the particular microenvironment of its site of infection, the role of each acquisition system in virulence can differ from a particular strain to another. In this review, we present the systems involved in metal transport by Enterobacteria and the main regulators responsible for their controlled expression. We also discuss the relative role of these systems depending on the pathogen and the tissues they infect.

An O island 172 encoded RNA helicase regulates the motility of Escherichia coli O157:H7

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 is a major cause of zoonotic food- and water-borne intestinal infections worldwide with clinical consequences ranging from mild diarrhoea to hemolytic uraemic syndrome. The genome of EHEC O157:H7 contains many regions of unique DNA that are referred to as O islands including the Shiga toxin prophages and pathogenicity islands encoding key virulence factors. However many of these O islands are of unknown function. In this study, genetic analysis was conducted on OI-172 which is a 44,434 bp genomic island with 27 open reading frames. Comparative genome analysis showed that O1-72 is a composite island with progressive gain of genes since O157:H7 evolved from its ancestral O55:H7. A partial OI-172 island was also found in 2 unrelated E. coli strains and 2 Salmonella strains. OI-172 encodes several putative helicases, one of which (Z5898) is a putative DEAH box RNA helicase. To investigate the function of Z5898, a deletion mutant (EDL933ΔZ5898) was constructed in the O157:H7 strain EDL933. Comparative proteomic analysis of the mutant with the wild-type EDL933 found that flagellin was down-regulated in the Z5898 mutant. Motility assay showed that EDL933ΔZ5898 migrated slower than the wild-type EDL933 and electron microscopy found no surface flagella. Quantitative reverse transcription PCR revealed that the fliC expression of EDL933ΔZ5898 was significantly lower while the expression of its upstream regulator gene, fliA, was not affected. Using a fliA and a fliC promoter - green fluorescent protein fusion contruct, Z5898 was found to affect only the fliC promoter activity. Therefore, Z5898 regulates the flagella based motility by exerting its effect on fliC. We conclude that OI-172 is a motility associated O island and hereby name it the MAO island.

Distribution of pathogenicity islands OI-122, OI-43/48, and OI-57 and a high-pathogenicity island in Shiga toxin-producing Escherichia coli

Pathogenicity islands (PAIs) play an important role in Shiga toxin-producing Escherichia coli (STEC) pathogenicity. The distribution of PAIs OI-122, OI-43/48, and OI-57 and a high-pathogenicity island (HPI) were determined among 98 STEC strains assigned to seropathotypes (SPTs) A to E. PCR and PCR-restriction fragment length polymorphism assays were used to identify 14 virulence genes that belonged to the four PAIs and to subtype eae and stx genes, respectively. Phylogenetic trees were constructed based on the sequences of pagC among 34 STEC strains and iha among 67 diverse pathogenic E. coli, respectively. Statistical analysis demonstrated that the prevalences of OI-122 (55.82%) and OI-57 (82.35%) were significantly greater in SPTs (i.e., SPTs A, B, and C) that are frequently associated with severe disease than in other SPTs. terC (62.5%) and ureC (62.5%) in OI-43/48 were also significantly more prevalent in SPTs A, B, and C than in SPTs D and E. In addition, OI-122, OI-57, and OI-43/48 and their associated virulence genes (except iha) were found to be primarily associated with eae-positive STEC, whereas HPI occurred independently of the eae presence. The strong association of OI-122, OI-43/48, and OI-57 with eae-positive STEC suggests in part that different pathogenic mechanisms exist between eae-positive and eae-negative STEC strains. Virulence genes in PAIs that are associated with severe diseases can be used as potential markers to aid in identifying highly virulent STEC.

Isolation and characterization of cytotoxic, aggregative Citrobacter freundii

Citrobacter freundii is an infrequent but established cause of diarrhea in humans. However, little is known of its genetic diversity and potential for virulence. We analyzed 26 isolates, including 12 from human diarrheal patients, 2 from human fecal samples of unknown diarrheal status, and 12 from animals, insects, and other sources. Pulsed field gel electrophoresis using XbaI allowed us to divide the 26 isolates into 20 pulse types, while multi-locus sequence typing using 7 housekeeping genes allowed us to divide the 26 isolates into 6 sequence types (STs) with the majority belonging to 4 STs. We analyzed adhesion and cytotoxicity to HEp-2 cells in these 26 strains. All were found to adhere to HEp-2 cells. One strain, CF74, which had been isolated from a goat, showed the strongest aggregative adhesion pattern. Lactate dehydrogenase (LDH) released from HEp-2 cells was evaluated as a measure of cytotoxicity, averaging 7.46%. Strain CF74 induced the highest level of LDH, 24.3%, and caused >50% cell rounding, detachment, and death. We named strain CF74 “cytotoxic and aggregative C. freundii.” Genome sequencing of CF74 revealed that it had acquired 7 genomic islands, including 2 fimbriae islands and a type VI secretion system island, all of which are potential virulence factors. Our results show that aggregative adherence and cytotoxicity play an important role in the pathogenesis of C. freundii.

Development of a markerless gene replacement system for Acidithiobacillus ferrooxidans and construction of a pfkB mutant

The extremely acidophilic, chemolithoautotrophic Acidithiobacillus ferrooxidans is an important bioleaching bacterium of great value in the metallurgical industry and environmental protection. In this report, a mutagenesis system based on the homing endonuclease I-SceI was developed to produce targeted, unmarked gene deletions in the strain A. ferrooxidans ATCC 23270. A targeted phosphofructokinase (PFK) gene (pfkB) mutant of A. ferrooxidans ATCC 23270 was constructed by homologous recombination and identified by PCR with specific primers as well as Southern blot analysis. This potential pfkB gene (AFE_1807) was also characterized by expression in PFK-deficient Escherichia coli cells, and heteroexpression of the PFKB protein demonstrated that it had functional PFK activity, though it was significantly lower (about 800-fold) than that of phosphofructokinase-2 (PFK-B) expressed by the pfkB gene from E. coli K-12. The function of the potential PFKB protein in A. ferrooxidans was demonstrated by comparing the properties of the pfkB mutant with those of the wild type. The pfkB mutant strain displayed a relatively reduced growth capacity in S(0) medium (0.5% [wt/vol] elemental sulfur in 9K basal salts solution adjusted to pH 3.0 with H(2)SO(4)), but the mutation did not completely prevent A. ferrooxidans from assimilating exogenous glucose. The transcriptional analysis of some related genes in central carbohydrate metabolism in the wild-type and mutant strains with or without supplementation of glucose was carried out by quantitative reverse transcription-PCR. This report suggests that the markerless mutagenesis strategy could serve as a model for functional studies of other genes of interest from A. ferrooxidans and multiple mutations could be made in a single A. ferrooxidans strain.

Enhanced Actin Pedestal Formation by Enterohemorrhagic Escherichia coli O157:H7 Adapted to the Mammalian Host

Upon intestinal colonization, enterohemorrhagic Escherichia coli (EHEC) induces epithelial cells to generate actin “pedestals” beneath bound bacteria, lesions that promote colonization. To induce pedestals, EHEC utilizes a type III secretion system to translocate into the mammalian cell bacterial effectors such as translocated intimin receptor (Tir), which localizes in the mammalian cell membrane and functions as a receptor for the bacterial outer membrane protein intimin. Whereas EHEC triggers efficient pedestal formation during mammalian infection, EHEC cultured in vitro induces pedestals on cell monolayers with relatively low efficiency. To determine whether growth within the mammalian host enhances EHEC pedestal formation, we compared in vitro-cultivated bacteria with EHEC directly isolated from infected piglets. Mammalian adaptation by EHEC was associated with a dramatic increase in the efficiency of cell attachment and pedestal formation. The amounts of intimin and Tir were significantly higher in host-adapted than in in vitro-cultivated bacteria, but increasing intimin or Tir expression, or artificially increasing the level of bacterial attachment to mammalian cells, did not enhance pedestal formation by in vitro-cultivated EHEC. Instead, a functional assay suggested that host-adapted EHEC translocate Tir much more efficiently than does in vitro-cultivated bacteria. These data suggest that adaptation of EHEC to the mammalian intestine enhances bacterial cell attachment, expression of intimin and Tir, and translocation of effectors that promote actin signaling.

Genome sequences and phylogenetic analysis of K88- and F18-positive porcine enterotoxigenic Escherichia coli

Porcine enterotoxigenic Escherichia coli (ETEC) continues to result in major morbidity and mortality in the swine industry via postweaning diarrhea. The key virulence factors of ETEC strains, their serotypes, and their fimbrial components have been well studied. However, most studies to date have focused on plasmid-encoded traits related to colonization and toxin production, and the chromosomal backgrounds of these strains have been largely understudied. Here, we generated the genomic sequences of K88-positive and F18-positive porcine ETEC strains and examined the phylogenetic distribution of clinical porcine ETEC strains and their plasmid-associated genetic content. The genomes of porcine ETEC strains UMNK88 and UMNF18 were both found to contain remarkable plasmid complements containing known virulence factors, potential novel virulence factors, and antimicrobial resistance-associated elements. The chromosomes of these strains also possessed several unique genomic islands containing hypothetical genes with similarity to classical virulence factors, although phage-associated genomic islands dominated the accessory genomes of these strains. Phylogenetic analysis of 78 clinical isolates associated with neonatal and porcine diarrhea revealed that a limited subset of porcine ETEC lineages exist that generally contain common toxin and fimbrial profiles, with many of the isolates belonging to the ST10, ST23, and ST169 multilocus sequencing types. These lineages were generally distinct from existing human ETEC database isolates. Overall, most porcine ETEC strains appear to have emerged from a limited subset of E. coli lineages that either have an increased propensity to carry plasmid-encoded virulence factors or have the appropriate ETEC core genome required for virulence.

Porcine IPEC-J2 intestinal epithelial cells in microbiological investigations

IPEC-J2 cells are porcine intestinal columnar epithelial cells that were isolated from neonatal piglet mid-jejunum. This cell line forms polarized monolayers with high transepithelial electrical resistance when cultured on 0.4 μm pore-size filters. The cell line is unique in that it is derived from small intestinal tissue (compared to the common human colon-derived lines HT-29, T84, and Caco-2) and is not transformed (compared to the porcine small intestinal line, IPI-2I). Porcine intestinal epithelial cells more closely mimic human physiology than analogous rodent cell lines (e.g. IEC-6 or IEC-18), which is important in studies of zoonotic infections; in addition, they provide specificity to study porcine-derived infections. IPEC-J2 cells are increasingly being used in microbiological studies to examine the interactions of various animal and human pathogens, including Salmonella enterica and pathogenic Escherichia coli, with intestinal epithelial cells. The IPEC-J2 cell line has also been employed in some probiotic studies, in which the cells have been used as an initial screening tool for adhesiveness and anti-inflammatory properties of the potential probiotic microorganisms. The validity of these studies is not clear as follow-up studies to assess the efficacy of the probiotics in vivo have not been published to date. The aims of this review are to provide a comprehensive overview of the microbiological studies that have been conducted with IPEC-J2 cells and a reference guide of key cellular and immune markers that have been identified in this cell line that may prove to be useful in future studies.

Specific expression of adherence-related genes in Escherichia coli O157:H7 strain EDL933 after heat treatment in ground beef

In this study, the expression of particular stress- and virulence-associated genes of Escherichia coli O157:H7 strain EDL933 in ground beef was investigated using real-time PCR. Specific gene expression in the food matrix was found in combination with heat treatment. In contrast to a treatment at 37°C, treatment at 48°C for 10 min resulted in increased expression of the genes eae, hcpA, iha, lpfA, and toxB. Adherence to human intestinal HT-29 cells was enhanced in bacterial cells inoculated and heat treated in ground beef. The expression of gadE, which encodes a main regulator of the glutamate system of the acid response, was reduced under these conditions. However, expression of rpoS and recA, which are involved in the establishment of stress responses, and Shiga toxin genes was not significantly different under the same conditions.

Adherence of Escherichia coli O157:H7 to epithelial cells in vitro and in pig gut loops is affected by bacterial culture conditions

The objectives of this study were to determine the effect of bacterial culture conditions on adherence of enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain 86-24 in vivo to pig enterocytes and to compare the results with adherence in vitro to cultured HEp-2 and IPEC-J2 cells. Growth of O157:H7 in MacConkey broth (MB) resulted in almost no adherence to both HEp-2 and IPEC-J2 cells; prior exposure of the bacteria to pH 2.5 reduced adherence. There was greater adherence by bacteria from static cultures than by those from shaken cultures and by bacteria cultured in brain-heart infusion (BHI) plus NaHCO₃ (BHIN) than by bacteria cultured in BHI. In contrast, in pig ileal loops, bacteria cultured in MB adhered well to enterocytes, and prior exposure to pH 2.5 had no effect on adherence. Among several media tested for their effect on bacterial adherence in the pig intestine, MB and BHIN proved to be the best. Bacterial adherence was dose-dependent and was more extensive in the ileum than in the colon. This study demonstrated that there are remarkable differences between culture conditions that promote adherence of an EHEC O157:H7 strain in vitro and in vivo, that culture conditions profoundly affect adherence to epithelial cells in vitro and in vivo, and that pig ileal loops are better suited to adherence studies than are colon loops.

Differential gene expression and adherence of Escherichia coli O157:H7 in vitro and in ligated pig intestines

BACKGROUND

Escherichia coli O157:H7 strain 86-24 grown in MacConkey broth (MB) shows almost no adherence to cultured epithelial cells but adheres well in pig ligated intestines. This study investigated the mechanisms associated with the difference between in-vitro and in-vivo adherence of the MB culture.

METHODOLOGY/PRINCIPAL FINDINGS

It was found that decreased adherence in vitro by bacteria grown in MB was mainly due to lactose, possibly implicating the involvement of carbon catabolite repression (CCR). Expression of selected virulence-related genes associated with adherence and CCR was then examined by quantitative PCR. When bacteria were grown in MB and Brain Heart Infusion with NaHCO(3) (BHIN) plus lactose, pH was reduced to 5.5-5.9 and there was a significant decrease in expression of the locus of enterocyte effacement (LEE) genes eae, tir, espD, grlA/R and ler, and an increase in cya (cAMP), and two negative regulators of the LEE, gadE and hfq. Putative virulence genes stcE, hlyA, ent and nleA were also decreased in vitro. Reversal of these changes was noted for bacteria recovered from the intestine, where transcripts for qseF and fis and putative virulence factors AidA(15), TerC and Ent/EspL2 were significantly increased, and transcripts for AIDA(48), Iha, UreC, Efa1A, Efa1B, ToxB, EhxA, StcE, NleA and NleB were expressed at high levels.

CONCLUSIONS/SIGNIFICANCE

Presence of lactose resulted in decreased expression of LEE genes and the failure of EHEC O157:H7 to adhere to epithelial cells in vitro but this repression was overcome in vivo. CCR and/or acidic pH may have played a role in repression of the LEE genes. Bacterial pathogens need to integrate their nutritional metabolism with expression of virulence genes but little is known of how this is done in E. coli O157:H7. This study indicates one aspect of the subject that should be investigated further.

Chromosomal instability in enterohaemorrhagic Escherichia coli O157:H7: impact on adherence, tellurite resistance and colony phenotype

Tellurite (Tel) resistant enterohaemorrhagic Escherichia coli (EHEC) O157:H7 is a global pathogen. In strain EDL933 Tel resistance (Tel^R) is encoded by duplicate ter cluster in O islands (OI) 43 and 48, which also harbour iha, encoding the adhesin and siderophore receptor Iha. We identified five EHEC O157:H7 strains that differentiate into large (L) colonies and small (S) colonies with high and low Tel minimal inhibitory concentrations (MICs) respectively. S colonies (Tel-MICs ≤ 4 µg ml⁻¹) sustained large internal deletions within the Tel^R OIs via homologous recombination between IS elements and lost ter and iha. Moreover, complete excision of the islands occurred by site-specific recombination between flanking direct repeats. Complete excision of OI 43 and OI 48 occurred in 1.81 × 10⁻³ and 1.97 × 10⁻⁴ cells in culture, respectively; internal deletion of OI 48 was more frequent (9.7 × 10⁻¹ cells). Under iron limitation that promotes iha transcription, iha-negative derivatives adhered less well to human intestinal epithelial cells and grew slower than did their iha-positive counterparts. Experiments utilizing iha deletion and complementation mutants identified Iha as the major factor responsible for these phenotypic differences. Spontaneous deletions affecting Tel^R OIs contribute to EHEC O157 genome plasticity and might impair virulence and/or fitness.

Catheterization of intestinal loops in ruminants does not adversely affect loop function

Catheterized intestinal loops may be a valuable model to elucidate key components of the host response to various treatments within the small intestine of ruminants. We examined whether catheterizing ileal loops in sheep affected the overall health of animals and intestinal function, whether a bacterial treatment could be introduced into the loops through the catheters, and whether broad-spectrum antibiotics could sterilize the loops. Escherichia coli cells transformed to express the GFP gene were introduced readily into the loops through the catheters, and GFP E. coli cells were localized within the injected loops. Catheterized loops, interspaces, and intact ileum exhibited no abnormalities in tissue appearance or electrical resistance. Expression of the IFNγ, IL1α, IL4, IL6, IL12p40, IL18, TGFβ1, and TNFα cytokine genes did not differ significantly among the intact ileum, catheterized loops, and interspaces, nor did the expression of the gene for inducible nitric oxide synthase. Broad-spectrum antibiotics administered during surgery did not sterilize the loops or interspaces and did not substantively change the composition of the microbiota. However, antibiotics reduced the overall number of bacterial cells within the loop and the relative abundance of community constituents. We concluded that catheterization of intestinal loops did not adversely affect health or loop function in sheep. Furthermore, allowing animals to recover fully from surgery and to clear pharmaceuticals will remove any confounding effects due to these factors, making catheterized intestinal loops a feasible model for studying host responses in ruminants.

Verocytotoxigenic (Shiga toxin-producing) Escherichia coli: virulence factors and pathogenicity in the farm to fork paradigm

Verocytotoxigenic Escherichia coli (VTEC) are a good example of the evolution and emergence of pathogenic E. coli. Unknown before the late 1970s, these bacteria are a major cause of hemorrhagic colitis and hemolytic uremic syndrome worldwide. The production of verocytotoxins is the main virulence feature of VTEC but cannot be solely responsible for full pathogenicity. VTEC associated with severe human disease are usually capable of colonizing the intestinal mucosa with a characteristic attaching-and-effacing mechanism, genetically governed by the locus of enterocyte effacement, and possess other mobile genetic elements carrying additional virulence genes such as plasmids, phages, and pathogenicity islands (e.g., O-I 122). Despite the huge amount of data collected after the sequencing of the full genome of VTEC O157, the virulence and the evolution of the different VTEC serotypes have only been partially unraveled. A greater understanding of the factors governing the development of severe disease in humans and the colonization of animal hosts must be achieved before effective intervention strategies aimed at the reduction of the burden of infection can be developed. Defining all the factors characterizing a fully pathogenic VTEC strain will be crucial to improve the efficacy of the diagnosis of human infections, the surveillance of animal reservoirs, the assessment of public health risks, and the development of control interventions. An overview of the VTEC virulence factors, including their genetic basis and function, would start this process and is the objective of this article.