Characterization of a shiga toxin-, intimin-, and enterotoxin hemolysin-producing Escherichia coli ONT:H25 strain commonly isolated from healthy cattle

Escherichia coli O157:H7 Curli Fimbriae Promotes Biofilm Formation, Epithelial Cell Invasion, and Persistence in Cattle

Escherichia coli O157:H7 (O157) is noninvasive and a weak biofilm producer; however, a subset of O157 are exceptions. O157 ATCC 43895 forms biofilms and invades epithelial cells. Tn5 mutagenesis identified a mutation responsible for both phenotypes. The insertion mapped within the curli csgB fimbriae locus. Screening of O157 strains for biofilm formation and cell invasion identified a bovine and a clinical isolate with those characteristics. A single base pair A to T transversion, intergenic to the curli divergent operons csgDEFG and csgBAC, was present only in biofilm-producing and invasive strains. Using site-directed mutagenesis, this single base change was introduced into two curli-negative/noninvasive O157 strains and modified strains to form biofilms, produce curli, and gain invasive capability. Transmission electron microscopy (EM) and immuno-EM confirmed curli fibers. EM of bovine epithelial cells (MAC-T) co-cultured with curli-expressing O157 showed intracellular bacteria. The role of curli in O157 persistence in cattle was examined by challenging cattle with curli-positive and -negative O157 and comparing carriage. The duration of bovine colonization with the O157 curli-negative mutant was shorter than its curli-positive isogenic parent. These findings definitively demonstrate that a single base pair stably confers biofilm formation, epithelial cell invasion, and persistence in cattle.

Complete Genome Sequence of Broad-Host-Range Shiga Toxin-Converting Bacteriophage SH2026Stx1, Isolated from Escherichia coli O157:H7

The Shiga toxin-encoding phage SH2026Stx1 was isolated from Escherichia coli O157:H7 strain 2026. SH2026Stx1 and its detoxified derivative can infect a broad range of E. coli strains, including commensal, enteropathogenic, and enteroaggregative strains. We report here the complete genome sequence of phage SH2026Stx1 and its important features.

High-Quality Complete Genome Sequences of Three Bovine Shiga Toxin-Producing Escherichia coli O177:H- (fliCH25) Isolates Harboring Virulent stx2 and Multiple Plasmids

Shiga toxin-producing Escherichia coli (STEC) bacteria are zoonotic pathogens. We report here the high-quality complete genome sequences of three STEC O177:H- (fliCH25) strains, SMN152SH1, SMN013SH2, and SMN197SH3. The assembled genomes consisted of one optical map-verified circular chromosome for each strain, plus two plasmids for SMN013SH2 and three plasmids for SMN152SH1 and SMN197SH3, respectively.

Serotyping, antibiotic susceptibility, and virulence genes screening of Escherichia coli isolates obtained from diarrheic buffalo calves in Egyptian farms

AIM

In Egypt as in many other countries, river water buffalo (Bubalus bubalis) is considered an important source of high-quality milk and meat supply. The objective of this study was to investigate serotypes, virulence genes, and antibiotic resistance determinants profiles of Escherichia coli isolated from buffalo at some places in Egypt; noticibly, this issue was not discussed in the country yet.

MATERIALS AND METHODS

A number of 58 rectal samples were collected from diarrheic buffalo calves in different regions in Egypt, and bacteriological investigated for E. coli existence. The E. coli isolates were biochemically, serologicaly identified, tested for antibiotic susceptibility, and polymerase chain reaction (PCR) analyzed for the presence of antibiotic resistance determinants and virulence genes.

RESULTS

Overall 14 isolates typed as E. coli (24.1%); 6 were belonged to serogroup O78 (10.3%), followed by O125 (4 isolates, 6.9%), then O158 (3 isolates, 5.2%) and one isolate O8 (1.7%), among them, there were 5 E. coli isolates showed a picture of hemolysis (35.7%). The isolates exhibited a high resistance to β lactams over 60%, followed by sulfa (50%) and aminoglucoside (42.8%) group, in the same time the isolates were sensitive to quinolone, trimethoprim-sulfamethoxazole, tetracycline (100%), and cephalosporine groups (71.4%). A multiplex PCR was applied to the 14 E. coli isolates revealed that all were carrying at least one gene, as 10 carried blaTEM (71.4%), 8 Sul1 (57.1%), and 6 aadB (42.8%), and 9 isolates could be considered multidrug resistant (MDR) by an incidence of 64.3%. A PCR survey was stratified for the most important E. coli virulence genes, and showed the presence of Shiga toxins in 9 isolates carried either one or the two Stx genes (64.3%), 5 isolates carried hylA gene (35.7%), and eae in 2 isolates only (14.3%), all isolates carried at least one virulence gene except two (85.7%).

CONCLUSION

The obtained data displayed that in Egypt, buffalo as well as other ruminants could be a potential source of MDR pathogenic E. coli variants which have a public health importance.

Optimizing the Protection of Cattle against Escherichia coli O157:H7 Colonization through Immunization with Different Combinations of H7 Flagellin, Tir, Intimin-531 or EspA

Enterohemorrhagic Escherichia coli (EHEC) are important human pathogens, causing hemorrhagic colitis and hemolytic uraemic syndrome in humans. E. coli O157:H7 is the most common serotype associated with EHEC infections worldwide, although other non-O157 serotypes cause life-threatening infections. Cattle are a main reservoir of EHEC and intervention strategies aimed at limiting EHEC excretion from cattle are predicted to lower the risk of human infection. We have previously shown that immunization of calves with recombinant versions of the type III secretion system (T3SS)-associated proteins EspA, intimin and Tir from EHEC O157:H7 significantly reduced shedding of EHEC O157 from experimentally-colonized calves, and that protection could be augmented by the addition of H7 flagellin to the vaccine formulation. The main aim of the present study was to optimize our current EHEC O157 subunit vaccine formulations by identifying the key combinations of these antigens required for protection. A secondary aim was to determine if vaccine-induced antibody responses exhibited cross-reactive potential with antigens from other EHEC serotypes. Immunization with EspA, intimin and Tir resulted in a reduction in mean EHEC O157 shedding following challenge, but not the mean proportion of calves colonized. Removal of Tir resulted in more prolonged shedding compared with all other groups, whereas replacement of Tir with H7 flagellin resulted in the highest levels of protection, both in terms of reducing both mean EHEC O157 shedding and the proportion of colonized calves. Immunization of calves with recombinant EHEC O157 EspA, intimin and Tir resulted in the generation of antibodies capable of cross-reacting with antigens from non-O157 EHEC serotypes, suggesting that immunization with these antigens may provide a degree of cross-protection against other EHEC serotypes. Further studies are now required to test the efficacy of these vaccines in the field, and to formally test the cross-protective potential of the vaccines against other non-O157 EHEC.

SdiA aids enterohemorrhagic Escherichia coli carriage by cattle fed a forage or grain diet

Enterohemorrhagic Escherichia coli (EHEC) causes hemorrhagic colitis and life-threatening complications. The main reservoirs for EHEC are healthy ruminants. We reported that SdiA senses acyl homoserine lactones (AHLs) in the bovine rumen to activate expression of the glutamate acid resistance (gad) genes priming EHEC's acid resistance before they pass into the acidic abomasum. Conversely, SdiA represses expression of the locus of enterocyte effacement (LEE) genes, whose expression is not required for bacterial survival in the rumen but is necessary for efficient colonization at the rectoanal junction (RAJ) mucosa. Our previous studies show that SdiA-dependent regulation was necessary for efficient EHEC colonization of cattle fed a grain diet. Here, we compared the SdiA role in EHEC colonization of cattle fed a forage hay diet. We detected AHLs in the rumen of cattle fed a hay diet, and these AHLs activated gad gene expression in an SdiA-dependent manner. The rumen fluid and fecal samples from hay-fed cattle were near neutrality, while the same digesta samples from grain-fed animals were acidic. Cattle fed either grain or hay and challenged with EHEC orally carried the bacteria similarly. EHEC was cleared from the rumen within days and from the RAJ mucosa after approximately one month. In competition trials, where animals were challenged with both wild-type and SdiA deletion mutant bacteria, diet did not affect the outcome that the wild-type strain was better able to persist and colonize. However, the wild-type strain had a greater advantage over the SdiA deletion mutant at the RAJ mucosa among cattle fed the grain diet.

Food microbe tracker: a web-based tool for storage and comparison of food-associated microbes

Large amounts of molecular subtyping information are generated by the private sector, academia, and government agencies. However, use of subtype data is limited by a lack of effective data storage and sharing mechanisms that allow comparison of subtype data from multiple sources. Currently available subtype databases are generally limited in scope to a few data types (e.g., MLST. net) or are not publicly available (e.g., PulseNet). We describe the development and initial implementation of Food Microbe Tracker, a public Web-based database that allows archiving and exchange of a variety of molecular subtype data that can be cross-referenced with isolate source data, genetic data, and phenotypic characteristics. Data can be queried with a variety of search criteria, including DNA sequences and banding pattern data (e.g., ribotype or pulsed-field gel electrophoresis type). Food Microbe Tracker allows the deposition of data on any bacterial genus and species, bacteriophages, and other viruses. The bacterial genera and species that currently have the most entries in this database are Listeria monocytogenes, Salmonella, Streptococcus spp., Pseudomonas spp., Bacillus spp., and Paenibacillus spp., with over 40,000 isolates. The combination of pathogen and spoilage microorganism data in the database will facilitate source tracking and outbreak detection, improve discovery of emerging subtypes, and increase our understanding of transmission and ecology of these microbes. Continued addition of subtyping, genetic or phenotypic data for a variety of microbial species will broaden the database and facilitate large-scale studies on the diversity of food-associated microbes.

The distribution of Escherichia coli serovars, virulence genes, gene association and combinations and virulence genes encoding serotypes in pathogenic E. coli recovered from diarrhoeic calves, sheep and goat

Ruminants, especially cattle, have been implicated as a principal reservoir of one of the enterovirulent Escherichia coli pathotypes. The detection of the virulence genes in diarrhoeic calves and small ruminants has not been studied in Egypt. To determine the occurrence, serotypes and the virulence gene markers, stx1, stx2, hylA, Flic(h7) , stb, F41, K99, sta, F17, LT-I, LT-II and eae, rectal swabs were taken from diarrhoeic calves, sheep and goats and subjected to bacterial culture and PCR. The E. coli prevalence rate in the diarrhoeic animals was 63.6% in calves, 27.3% in goat and 9.1% in sheep. The 102 E. coli strains isolated from the calves, goat and sheep were 100% haemolytic non-verotoxic and fitted into the Eagg group. The isolates belonged to seven O serogroups (O25, O78, O86, O119, O158, O164 and O157). The eae gene was detected in six of the strains isolated from the calves. The 102 bovine, ovine and caprine E. coli strains isolated in this study were negative for stx1, stx2, F41, LT-I and Flic(h7) genes. The highest gene combinations were found to occur in the form of 24/102 isolates (23.5%) that carried the F17 gene predominantly associated with eaeA, hylA, K99 and Stb genes in the calves, while the hylA, K99 and Sta were the only genes found to be in conjunction in both calves and goats (6/102; 5.9% each). Our data show that in Egypt, large and small ruminants could be a potential source of infection in humans.

Characterization of verotoxigenic Escherichia coli (VTEC) isolates from faeces of small ruminants and environmental samples in southern Jordan

This study was conducted to determine the prevalence rate of VTEC in slaughtered sheep and goats and to evaluate the contamination rate of VTEC in slaughterhouses and butchers' shops in southern Jordan. 201 E. coli isolates from animals' faecal samples and 33 E. coli isolates from slaughterhouse/butcher shop samples were characterized by multiplex PCR (mPCR) reaction for detection of stx1, stx2, eae A and E-hly A virulent genes. Twenty-six virulent E. coli isolates were characterized by mPCR to seven different virulent patterns: stx1, stx1+stx2, stx1+eae A, stx1+E-hly A, stx1+eae A+E-hly A, eae A and E-hly A. It was found that VTEC comprised 6.4% and 21% of the total E. coli isolates from slaughtered small ruminants and slaughterhouses/ butchers' shops, respectively. The VTEC comprised 76.2% of the virulent isolates. The proportion of stx1:stx1+stx2 patterns was 19:1. It was found that the characterized complex VTEC (containing eae A and/or E-hly A) possessed three virulence patterns, including (VTEC) stx1 +eae A, (VTEC/EHEC) stx1 +E-hly A and (VTEC/EHEC) stx1 +eae A +E-hly A in percentages of 30%, 25% and 10%, respectively, in relation to the total VTEC isolates. Only two VTEC isolates were characterized as E. coli O157 and O26 serotypes, as highly pathogenic strains. Each of the O157 and O26 VTEC isolates was in a percentage of 0.4% in relation to the total E. coli isolates with virulent patterns stx1, eae A and E-hly A. The rest of the VTEC isolates were non-O157 VTEC. The antibiotic sensitivity test showed that the isolated VTEC was highly sensitive to gentamicin and co-trimoxazole and highly resistant to tetracycline and ampicillin.

Heat-labile enterotoxin promotes Escherichia coli adherence to intestinal epithelial cells

Given recent evidence suggesting that the heat-labile enterotoxin (LT) provides a colonization advantage for enterotoxigenic Escherichia coli (ETEC) in vivo, we hypothesized that LT preconditions the host intestinal epithelium for ETEC adherence. To test this hypothesis, we used an in vitro model of ETEC adherence to examine the role of LT in promoting bacterium-host interactions. We present data demonstrating that elaboration of LT promotes a significant increase in E. coli adherence. This phenotype is primarily dependent on the inherent ADP-ribosylation activity of this toxin, with a secondary role observed for the receptor-binding LT-B subunit. Rp-3',5'-cyclic AMP (cAMP), an inhibitor of protein kinase A, was sufficient to abrogate LT's ability to promote subsequent bacterial adherence. Increased adherence was not due to changes in the surface expression of the host receptor for the K88ac adhesin. Evidence is also presented for a role for bacterial sensing of host-derived cAMP in promoting adherence to host cells.

Characterization of an Escherichia coli O157:H7 O-antigen deletion mutant and effect of the deletion on bacterial persistence in the mouse intestine and colonization at the bovine terminal rectal mucosa

Escherichia coli O157:H7 causes hemorrhagic colitis and the life-threatening hemolytic-uremic syndrome in humans and transiently colonizes healthy cattle at the terminal rectal mucosa. To investigate the role of the O antigen in persistence and colonization in the animal host, we generated an E. coli O157:H7 mutant defective in the synthesis of the lipopolysaccharide side chain (O antigen) by deletion of a putative perosamine synthetase gene (per) in the rfb cluster. The lack of O antigen was confirmed by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and anti-O157 antibody. The growth rate and cell membrane permeability of the Deltaper mutant were similar to the growth rate and cell membrane permeability of the wild type. Changes in membrane and secreted proteins were observed, but the expression of intimin, EspA, and EspB, implicated in bacterial intestinal colonization, was not altered, as determined by immunoblotting and reverse transcription-PCR. Similar to other O-antigen deletion mutants, the Deltaper mutant was pleiotropic for autoaggregation and motility (it was FliC negative as determined by immunoblotting and flagellum negative as determined by electron microscopy). The abilities of the mutant and the wild type to persist in the murine intestine and to colonize the bovine terminal rectal mucosa were compared. Mice fed the Deltaper mutant shed lower numbers of bacteria (P < 0.05) over a shorter time than mice fed the wild-type or complemented strain. After rectal application in steers, lower numbers of the Deltaper mutant than of the wild type colonized the rectoanal junction mucosa, and the duration of the colonization was shorter (P < 0.05). Our previous work showed that flagella do not influence E. coli O157:H7 colonization at the bovine terminal rectal mucosa, so the current findings suggest that the O antigen contributes to efficient bovine colonization.

Nanowire-based delivery of Escherichia coli O157 shiga toxin 1 A subunit into human and bovine cells

Silica nanowires (NWs) were used to introduce the Shiga toxin type 1 A subunit (StxA1) into cultured bovine and human epithelial cells. We extended technology developed in our laboratories that employs fibronectin (Fn) to induce integrin-mediated uptake of NWs by coating NWs with StxA1 and Fn. The bonding strengths of Fn and StxA1 to the surface of NWs were measured by X-ray photoelectron spectroscopy. This technique demonstrated complex interactions between Fn, StxA1, and the NWs. Neutral red cytotoxicity assays and field emission scanning electron microscopy confirmed that the NW-StxA1-Fn complexes were effectively internalized and caused cell death. This indicates that NWs can carry StxA1 and potentially other toxic or therapeutic agents into eukaryotic cells. Ongoing studies include improved functionalizing of NWs aimed at increasing internalization efficiency and substituting ligands for specific cell targeting.

Shiga toxin-producing Escherichia coli isolated from patients with diarrhoea in Bangladesh

The prevalence of Shiga toxin-producing Escherichia coli (STEC) and its characteristics were determined among hospitalized patients with diarrhoea and children with diarrhoea in an urban slum community of Dhaka city using sensitive culture and PCR methods. Stool samples were collected from 410 patients with diarrhoea enrolled in the 2% surveillance system (every 50th patient attending the hospital with diarrhoeal disease is included) at the ICDDR,B hospital and from 160 children of 2-5 years of age with diarrhoea living in an urban slum in Dhaka, between September 2004 and April 2005. Shiga toxin genes (stx) were detected by multiplex PCR in the enrichment broth of nine samples (2.2%) from hospitalized patients and 11 samples (6.9%) from the community patients. STEC was isolated from five stool samples with positive PCR results using a colony patch technique. All five isolates were positive in the Vero cell assay and PCR fragments of stx genes were confirmed by sequencing. Two isolates were positive for the E. coli attaching-and-effacing (eae) gene and four were positive for the enterohaemolysin (hlyEHEC) gene and enterohaemolysin production. The five isolates belonged to five different serotypes:O32:H25, O2:H45, O76:H19, ONT:H25 and ONT:H19. It can be concluded that STEC is not a common pathogen in Bangladesh among hospitalized patients with diarrhoea nor among mild cases of diarrhoea in the community.

Prevalence and pathogenicity of Shiga toxin-producing Escherichia coli in beef cattle and their products1,2

During the past 23 yr, a large number of human illness outbreaks have been traced worldwide to consumption of undercooked ground beef and other beef products contaminated with Shiga toxin-producing Escherichia coli (STEC). Although several routes exist for human infection with STEC, beef remains a main source. Thus, beef cattle are considered reservoirs of O157 and nonO157 STEC. Because of the global nature of the food supply, safety concerns with beef will continue, and the challenges facing the beef industry will increase at the production and processing levels. To be prepared to address these concerns and challenges, it is critical to assess the beef cattle role in human infection with STEC. Because most STEC outbreaks in the United States were traced to beef containing E. coli O157:H7, the epidemiological studies have focused on the prevalence of this serotype in beef and beef cattle. Worldwide, however, additional STEC serotypes (e.g., members of the O26, O91, O103, O111, O118, O145, and O166 serogroups) have been isolated from beef and caused human illnesses ranging from bloody diarrhea and hemorrhagic colitis to the life-threatening hemolytic uremic syndrome (HUS). To provide a global assessment of the STEC problem, published reports on beef and beef cattle in the past 3 decades were evaluated. The prevalence rates of E. coli O157 ranged from 0.1 to 54.2% in ground beef, from 0.1 to 4.4% in sausage, from 1.1 to 36.0% in various retail cuts, and from 0.01 to 43.4% in whole carcasses. The corresponding prevalence rates of nonO157 STEC were 2.4 to 30.0%, 17.0 to 49.2%, 11.4 to 49.6%, and 1.7 to 58.0%, respectively. Of the 162 STEC serotypes isolated from beef products, 43 were detected in HUS patients and 36 are known to cause other human illnesses. With regard to beef cattle, the prevalence rates of E. coli O157 ranged from 0.3 to 19.7% in feedlots and from 0.7 to 27.3% on pasture. The corresponding prevalence rates of nonO157 STEC were 4.6 to 55.9% and 4.7 to 44.8%, respectively. Of the 373 STEC serotypes isolated from cattle feces or hides, 65 were detected in HUS patients and 62 are known to cause other human illnesses. The results indicated the prevalence of a large number of pathogenic STEC in beef and beef cattle at high rates and emphasized the critical need for control measures to assure beef safety.

Expression profiles of bovine genes in the rectoanal junction mucosa during colonization with Escherichia coli O157:H7

A bovine-specific cDNA microarray was used to characterize gene expression in the bovine rectoanal junction mucosa in response to Escherichia coli O157:H7 colonization, and results were confirmed using quantitative real-time PCR. The results showed involvement of cell processes including immune response, cell structure/dynamics, signal transduction, intercellular communication, and metabolism.

Role of Escherichia coli O157:H7 virulence factors in colonization at the bovine terminal rectal mucosa

The human pathogen Escherichia coli O157:H7 causes hemorrhagic colitis and life-threatening sequelae and transiently colonizes healthy cattle at the terminal rectal mucosa. This study analyzed virulence factors important for the clinical manifestations of human E. coli O157:H7 infection for their contribution to the persistence of E. coli in cattle. The colonizing ability of E. coli O157:H7 was compared with those of nonpathogenic E. coli K-12 and isogenic deletion mutants missing Shiga toxin (Stx), the adhesin intimin, its receptor Tir, hemolysin, or the approximately 92-kb pO157. Fully ruminant steers received a single rectal application of one E. coli strain so that effects of mucosal attachment and survival at the terminal rectum could be measured without the impact of bacterial passage through the entire gastrointestinal tract. Colonization was monitored by sensitive recto-anal junction mucosal swab culture. Nonpathogenic E. coli K-12 did not colonize as well as E. coli O157:H7 at the bovine terminal rectal mucosa. The E. coli O157:H7 best able to persist had intimin, Tir, and the pO157. Strains missing even one of these factors were recovered in lower numbers and were cleared faster than the wild type. In contrast, E. coli O157:H7 strains that were missing Stx or hemolysin colonized like the wild type. For these three strains, the number of bacteria increased between days 1 and 4 postapplication and then decreased slowly. In contrast, the numbers of noncolonizing strains (K-12, delta tir, and delta eae) decreased from the day of application. These patterns consistently predicted long-term colonization or clearance of the bacteria from the bovine terminal rectal mucosa.