Identification, characterization, and distribution of a Shiga toxin 1 gene variant (stx(1c)) in Escherichia coli strains isolated from humans

A Comprehensive Review on Shiga Toxin Subtypes and Their Niche-Related Distribution Characteristics in Shiga-Toxin-Producing E. coli and Other Bacterial Hosts

Shiga toxin (Stx), the main virulence factor of Shiga-toxin-producing E. coli (STEC), was first discovered in Shigella dysenteriae strains. While several other bacterial species have since been reported to produce Stx, STEC poses the most significant risk to human health due to its widespread prevalence across various animal hosts that have close contact with human populations. Based on its biochemical and molecular characteristics, Shiga toxin can be grouped into two types, Stx1 and Stx2, among which a variety of variants and subtypes have been identified in various bacteria and host species. Interestingly, the different Stx subtypes appear to vary in their host distribution characteristics and in the severity of diseases that they are associated with. As such, this review provides a comprehensive overview on the bacterial species that have been recorded to possess stx genes to date, with a specific focus on the various Stx subtype variants discovered in STEC, their prevalence in certain host species, and their disease-related characteristics. This review provides a better understanding of the Stx subtypes and highlights the need for rapid and accurate approaches to toxin subtyping for the proper evaluation of the health risks associated with Shiga-toxin-related bacterial food contamination and human infections.

The Importance of Shiga Toxin-Producing Escherichia coli O145:NM[H28]/H28 Infections in Argentina, 1998–2020

Shiga toxin-producing Escherichia coli (STEC) is known as a pathogen associated with food-borne diseases. The STEC O145 serogroup has been related with acute watery diarrhea, bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS). Argentina has the highest rate of HUS worldwide with 70% of the cases associated with STEC infections. We aimed to describe the epidemiology and genetic diversity of STEC O145 strains isolated across Argentina between 1998–2020. The strains isolated from 543 cases of human disease and four cattle, were pheno-genotipically characterized. Sequencing of five strains was performed. The strains were serotyped as O145:NM[H28]/H28, O145:H25, and O145:HNT, and mainly characterized as O145:NM[H28]/stx_2a/eae/ehxA (98.1%). The results obtained by sequencing were consistent with those obtained by traditional methods and additional genes involved in different mechanisms of the pathogen were observed. In this study, we confirmed that STEC O145 strains are the second serogroup after O157 and represent 20.3% of HUS cases in Argentina. The frequency of STEC O145 and other significant serogroups is of utmost importance for public health in the country. This study encourages the improvement of the surveillance system to prevent severe cases of human disease.

Bacteriophages: A possible solution to combat enteropathogenic Escherichia coli infections in neonatal goats

Due to awareness and benefits of goat rearing in developing economies, goats' significance is increasing. Unfortunately, these ruminants are threatened via multiple bacterial pathogens such as Enteropathogenic Escherichia coli (EPEC). In goat kids and lambs, EPEC causes gastrointestinal disease leading to substantial economic losses for farmers and may also pose a threat to public health via the spread of zoonotic diseases. Management of infection is primarily based on antibiotics, but the need for new therapeutic measures as an alternative to antibiotics is becoming vital because of the advent of antimicrobial resistance (AMR). The prevalence of EPEC was established using bfpA gene, uspA gene, and Stx1 gene, followed by phylogenetic analysis using Stx1 gene. The lytic activity of the isolated putative coliphages was tested on multi-drug resistant strains of EPEC. It was observed that a PCR based approach is more effective and rapid as compared to phenotypic tests of Escherichia coli virulence. It was also established that the isolated bacteriophages exhibited potent antibacterial efficacy in-vitro, with some of the isolates (16%) detected as T4 and T4-like phages based on gp23 gene. Hence, bacteriophages as therapeutic agents may be explored as an alternative to antibiotics in managing public, livestock and environmental health in this era of AMR.

Genetic and antimicrobial resistance profiles of non-O157 Shiga toxin-producing Escherichia coli from different sources in Egypt

BACKGROUND

The Shiga toxin-producing Escherichia coli (STEC) represented a great risk to public health. In this study, 60 STEC strains recovered from broiler and duck fecal samples, cow's milk, cattle beef, human urine, and ear discharge were screened for 12 virulence genes, phenotypic and genotypic antimicrobial resistance, and multiple-locus variable-number tandem-repeat analysis (MLVA).

RESULTS

The majority of strains harbored Shiga toxin 1 (stx₁) and stx_1d, stx₂ and stx_2e, and ehxA genes, while a minority harbored stx_2c subtype and eaeA. We identified 10 stx gene combinations; most of strains 31/60 (51.7%) exhibited four copies of stx genes, namely the stx₁, stx_1d, stx₂, and stx_2e, and the strains exhibited a high range of multiple antimicrobial resistance indices. The resistance genes blaCTX-M-1 and blaTEM were detected. For the oxytetracycline resistance genes, most of strains contained tetA, tetB, tetE, and tetG while the tetC was present at low frequency. MLVA genotyping resolved 26 unique genotypes; genotype 21 was highly prevalent. The six highly discriminatory loci DI = 0.9138 are suitable for the preliminary genotyping of STEC from animals and humans.

CONCLUSIONS

The STEC isolated from animals are virulent, resistant to antimicrobials, and genetically diverse, thus demands greater attention for the potential risk to human.

Molecular Biology of Escherichia Coli Shiga Toxins' Effects on Mammalian Cells

Shiga toxins (Stxs), syn. Vero(cyto)toxins, are potent bacterial exotoxins and the principal virulence factor of enterohemorrhagic Escherichia coli (EHEC), a subset of Shiga toxin-producing E. coli (STEC). EHEC strains, e.g., strains of serovars O157:H7 and O104:H4, may cause individual cases as well as large outbreaks of life-threatening diseases in humans. Stxs primarily exert a ribotoxic activity in the eukaryotic target cells of the mammalian host resulting in rapid protein synthesis inhibition and cell death. Damage of endothelial cells in the kidneys and the central nervous system by Stxs is central in the pathogenesis of hemolytic uremic syndrome (HUS) in humans and edema disease in pigs. Probably even more important, the toxins also are capable of modulating a plethora of essential cellular functions, which eventually disturb intercellular communication. The review aims at providing a comprehensive overview of the current knowledge of the time course and the consecutive steps of Stx/cell interactions at the molecular level. Intervention measures deduced from an in-depth understanding of this molecular interplay may foster our basic understanding of cellular biology and microbial pathogenesis and pave the way to the creation of host-directed active compounds to mitigate the pathological conditions of STEC infections in the mammalian body.

Oral immunization of mice with Lactococcus lactis expressing Shiga toxin truncate confers enhanced protection against Shiga toxins of Escherichia coli O157:H7 and Shigella dysenteriae

Regardless of the communal impact of Shiga toxins, till today neither a specific treatment nor licensed vaccine is available. Lactococcus lactis (L. lactis), generally regarded as safe organism, is well known to provide a valuable approach regarding the oral delivery of vaccines. This study was undertaken to evaluate the protective efficacy of Stx2a1 expressed in nisin-inducible L. lactis, against Shiga toxins (Stx1, Stx2) in mouse model. Oral immunization of BALB/c mice with LL-Stx2a1 elicited significant serum antibody titer with elevated fecal and serum IgA, along with minimized intestinal and kidney damage resulting in survival of immunized animals at 84% and 100% when challenged with 10 × LD₅₀ of Escherichia coli O157 and Shigella dysenteriae toxins, respectively. HeLa cells incubated with immune sera and toxin mixture revealed high neutralizing capacity with 90% cell survivability against both the toxins. Mice immunized passively with both toxins and antibody mixture survived the observation period of 15 days, and the controls administered with sham sera and toxins were succumbed to death within 3 days. Our results revealed protective efficacy and toxin neutralization ability of LL-Stx2a1, proposing it as an oral vaccine candidate against Shiga toxicity mediated by E. coli O157 and S. dysenteriae.

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.

DNA microarray-based assessment of virulence potential of Shiga toxin gene-carrying Escherichia coli O104:H7 isolated from feedlot cattle feces

Escherichia coli O104:H4, a hybrid pathotype reported in a large 2011 foodborne outbreak in Germany, has not been detected in cattle feces. However, cattle harbor and shed in the feces other O104 serotypes, particularly O104:H7, which has been associated with sporadic cases of diarrhea in humans. The objective of our study was to assess the virulence potential of Shiga toxin-producing E. coli (STEC) O104:H7 isolated from feces of feedlot cattle using DNA microarray. Six strains of STEC O104:H7 isolated from cattle feces were analyzed using FDA-E. coli Identification (ECID) DNA microarray to determine their virulence profiles and compare them to the human strains (clinical) of O104:H7, STEC O104:H4 (German outbreak strain), and O104:H21 (milk-associated Montana outbreak strain). Scatter plots were generated from the array data to visualize the gene-level differences between bovine and human O104 strains, and Pearson correlation coefficients (r) were determined. Splits tree was generated to analyze relatedness between the strains. All O104:H7 strains, both bovine and human, similar to O104:H4 and O104:H21 outbreak strains were negative for intimin (eae). The bovine strains were positive for Shiga toxin 1 subtype c (stx1c), enterohemolysin (ehxA), tellurite resistance gene (terD), IrgA homolog protein (iha), type 1 fimbriae (fimH), and negative for genes that code for effector proteins of type III secretory system. The six cattle O104 strains were closely related (r = 0.86-0.98) to each other, except for a few differences in phage related and non-annotated genes. One of the human clinical O104:H7 strains (2011C-3665) was more closely related to the bovine O104:H7 strains (r = 0.81-0.85) than the other four human clinical O104:H7 strains (r = 0.75-0.79). Montana outbreak strain (O104:H21) was more closely related to four of the human clinical O104:H7 strains than the bovine O104:H7 strains. None of the bovine E. coli O104 strains carried genes characteristic of E. coli O104:H4 German outbreak strain and unlike other human strains were also negative for Shiga toxin 2. Because cattle E. coli O104:H7 strains possess stx1c and genes that code for enterohemolysin and a variety of adhesins, the serotype has the potential to be a diarrheagenic foodborne pathogen in humans.

Overview of the role of Shiga toxins in porcine edema disease pathogenesis

Shiga toxin-producing Escherichia coli (STEC) have been implicated as the cause of enterotoxemias, such as hemolytic uremic syndrome in humans and edema disease (ED) of pigs. Stx1 and Stx2 are the most common types found in association with illness, but only Stx2e is associated with disease in the animal host. Porcine edema disease is a serious affection which can lead to dead causing great losses of weaned piglets. Stx2e is the most frequent Stx variant found in porcine feces and is considered the key virulence factor involved in the pathogenesis of porcine edema disease. Stx2e binds with higher affinity to Gb4 receptor than to Gb3 which could be due to amino acid changes in B subunit. Moreover, this subtype also binds to Forssman glycosphingolipids conferring upon Stx2e a unique promiscuous recognition feature. Manifestations of edema disease are caused by systemic effects of Stx2e with no significant morphologic changes in enterocytes. Endothelial cell necrosis in the brain is an early event in the pathogenesis of ED caused by Stx2e-producing STEC strains. Further studies are needed to generate techniques and tools which allow to understand the circulation and ecology of STEC strains in pigs even in resistant animals for diagnostic and epidemiological purposes.

Serogroups, subtypes and virulence factors of shiga toxin-producing Escherichia coli isolated from human, calves and goats in Kerman, Iran

AIM

The present study was conducted to detect the occurrence, serogroups, virulence genes and phylogenetic relationship of shiga toxin-producing Escherichia coli (STEC) in human, clave and goat in Kerman (southeast of Iran).

BACKGROUND

STEC have emerged as the important foodborne zoonotic pathogens causing human gastrointestinal disease and confirming the risk to public health.

METHODS

A total of 671 fecal samples were collected from diarrheic patients (n=395) and healthy calves (n=156) and goats (n=120) and screened for the presence of stx gene. Furthermore, the prevalence of stx1 and stx2 variants, serotypes (O157, O145, O103, O26, O111, O91, O128, and O45), phylogenetic groups and the presence of ehxA, eae, hylA, iha and saa virulence genes were studied.

RESULTS

Prevalence of STEC in human diarrheic isolates was 1.3% (5 isolates), in claves was 26.3% (41 isolates) and in goats was 27.5% (33 isolates). stx1 gene was the most prevalent variant and detected in 75 isolates. Furthermore, stx1c was the most predominant stx subtype, found in 56 isolates. The ehxA identified in 36 (45.6%) isolates, followed by iha 5 (6.3%), eaeA 4 (5.1%), hlyA 2 (2.5%) and saa 2 (2.5%). Most of the isolates belonged to phylogroup B1. Only two O26 and one O91 isolates were detected in our study.

CONCLUSION

Our results show that STEC strains were widespread among healthy domestic animals in the southeast of Iran.

Prevalence, virulence potential, and pulsed-field gel electrophoresis profiling of Shiga toxin-producing Escherichia coli strains from cattle

BACKGROUND

As a primary source of Shiga-toxin-producing Escherichia coli (STEC) infection, cattle are often targeted to develop strategies for reducing STEC contamination. Monitoring the virulence potentials of STEC isolates from cattle is important for tracing contamination sources, managing outbreaks or sporadic cases, and reducing the risks for human infection. This study aimed to investigate the prevalence of STEC in cattle farm samples in South Korea and to assess their virulence potentials.

RESULTS

In total, 63 STEC were isolated from 496 cattle farm samples, and temperature and rainfall affected STEC prevalence (p < 0.001). The O157 serogroup was most prevalent, followed by O108, O8, O84, O15, and O119. In the stx variant test, high prevalence of stx2a and stx2c (known to be associated with high STEC virulence) were observed, and stx2g, a bovine STEC variant, was detected in STEC O15 and O109. Additionally, stx1c was detected in eae-positive STEC, suggesting genetic dynamics among the virulence genes in the STEC isolates. STEC non-O157 strains were resistant to tetracycline (17.9%), ampicillin (14.3%), and cefotaxime (3.6%), while STEC O157 was susceptible to all tested antimicrobials, except cefotaxime. The antimicrobial resistance genes, bla_TEM (17.5%), tetB (6.3%), and tetC (4.8%), were only detected in STEC non-O157, whereas tetE (54.0%) was detected in STEC O157. AmpC was detected in all STEC isolates. Clustering was performed based on the virulence gene profiles, which grouped STEC O84, O108, O111, and O157 together as potentially pathogenic STEC strains. Finally, PFGE suggested the presence of a prototype STEC that continues to evolve by genetic mutation and causes within- and between-farm transmission within the Gyeonggi province.

CONCLUSIONS

Considerable numbers of STEC non-O157 were isolated from cattle farms, and the virulence and antimicrobial resistance features were different between the STEC O157 and non-O157 strains. STEC from cattle with virulence or antimicrobial resistance genes might represent a threat to public health and therefore, continual surveillance of both STEC O157 and non-O157 would be beneficial for controlling and preventing STEC-related illness.

Isolation of Shiga toxin-producing Escherichia coli harboring variant Shiga toxin genes from seafood

Background and Aim:

Shiga toxin-producing Escherichia coli (STEC) are important pathogens of global significance. STEC are responsible for numerous food-borne outbreaks worldwide and their presence in food is a potential health hazard. The objective of the present study was to determine the incidence of STEC in fresh seafood in Mumbai, India, and to characterize STEC with respect to their virulence determinants.

Materials and Methods:

A total of 368 E. coli were isolated from 39 fresh seafood samples (18 finfish and 21 shellfish) using culture-based methods. The isolates were screened by polymerase chain reaction (PCR) for the genes commonly associated with STEC. The variant Shiga toxin genes were confirmed by Southern blotting and hybridization followed by DNA sequencing.

Results:

One or more Shiga toxins genes were detected in 61 isolates. Of 39 samples analyzed, 10 (25.64%) samples harbored STEC. Other virulence genes, namely, eaeA (coding for an intimin) and hlyA (hemolysin A) were detected in 43 and 15 seafood isolates, respectively. The variant stx1 genes from 6 isolates were sequenced, five of which were found to be stx1d variants, while one sequence varied considerably from known stx1 sequences. Southern hybridization and DNA sequence analysis suggested putative Shiga toxin variant genes (stx2) in at least 3 other isolates.

Conclusion:

The results of this study showed the occurrence of STEC in seafood harboring one or more Shiga toxin genes. The detection of STEC by PCR may be hampered due to the presence of variant genes such as the stx1d in STEC. This is the first report of stx1d gene in STEC isolated from Indian seafood.

Postinfectious Hemolytic Uremic Syndrome

Post-infectious hemolytic uremic syndrome (HUS) is caused by specific pathogens in patients with no identifiable HUS-associated genetic mutation or autoantibody. The majority of episodes is due to infections by Shiga toxin (Stx) producing Escherichia coli (STEC). This chapter reviews the epidemiology and pathogenesis of STEC-HUS, including bacterial-derived factors and host responses. STEC disease is characterized by hematological (microangiopathic hemolytic anemia), renal (acute kidney injury) and extrarenal organ involvement. Clinicians should always strive for an etiological diagnosis through the microbiological or molecular identification of Stx-producing bacteria and Stx or, if negative, serological assays. Treatment of STEC-HUS is supportive; more investigations are needed to evaluate the efficacy of putative preventive and therapeutic measures, such as non-phage-inducing antibiotics, volume expansion and anti-complement agents. The outcome of STEC-HUS is generally favorable, but chronic kidney disease, permanent extrarenal, mainly cerebral complication and death (in less than 5 %) occur and long-term follow-up is recommended. The remainder of this chapter highlights rarer forms of (post-infectious) HUS due to S. dysenteriae, S. pneumoniae, influenza A and HIV and discusses potential interactions between these pathogens and the complement system.

Phage-mediated Shiga toxin (Stx) horizontal gene transfer and expression in non-Shiga toxigenic Enterobacter and Escherichia coli strains

Enterobacter cloacae M12X01451 strain recently identified from a clinical specimen produces a new Stx1 subtype (Stx1e) that was not neutralized by existing anti-Stx1 monoclonal antibodies. Acquisition of stx by Ent. cloacae is rare and origin/stability of stx1e in M12X01451 is not known. In this study, we confirmed the ability of Stx1a- and Stx1e-converting phages from an Escherichia coli O157:H7 strain RM8530 and M12X01451 respectively to infect several E. coli and Ent. cloacae strains. stx1e was detected in 97.5% and 72.5% of progenies of strains lysogenized by stx1e phage after 10 (T10) and 20 (T20) subcultures, versus 65% and 17.5% for stx1a gene. Infection of M12X01451 and RM8530 with each other's phages generated double lysogens containing both phages. stx1a was lost after T10, whereas the stx1e was maintained even after T20 in M12X01451 lysogens. In RM8530 lysogens, the acquired stx1e was retained with no mutations, but 20% of stx1a was lost after T20 ELISA and western blot analyses demonstrated that Stx1e was produced in all strains lysogenized by stx1e phage; however, Stx1a was not detected in any lysogenized strain. The study results highlight the potential risks of emerging Stx-producing strains via bacteriophages either in the human gastrointestinal tract or in food production environments, which are matters of great concern and may have serious impacts on human health.

Genetic features of human and bovine Escherichia coli O157:H7 strains isolated in Argentina

Shiga toxin-producing Escherichia coli (STEC) are important food-borne pathogens associated with human diseases. In Argentina, O157:H7 is the dominant serotype in hemolytic uremic syndrome (HUS) cases. Previously, we have described the almost exclusive circulation of human E. coli O157 strains belonging to the hypervirulent clade 8 in Neuquén Province. The aim of the present study was to investigate, by a broad molecular characterization, if this particular distribution of E. coli O157 clades in Neuquén is similar to the situation in other regions of the country and if it may be originated in a similar profile in cattle, its main reservoir. Two-hundred and eighty O157 strains (54 bovine and 226 human) isolated between 2006 and 2008 in different regions of Argentina were studied. All strains harbored rfbO157, fliCH7, eae, and ehxA genes. The predominant genotype was stx2a/stx2c in human (76.1%) and bovine (55.5%) strains. All human isolates tested by Lineage-Specific Polymorphism Assay (LSPA-6), were lineage I/II; among bovine strains, 94.1% belonged to lineage I/II and 5.9% to lineage I. No LSPA-6 lineage II isolates were detected. Single nucleotide polymorphism (SNP) analysis has revealed the existence of nine clade phylogenetic groups. In our clinical strains collection, 87.6% belonged to the hypervirulent clade 8, and 12.4% were classified as clade 4/5. In bovine isolates, 59.3% strains were clade 8, 33.3% clade 4/5 and 7.4% clade 3. More than 80% of human strains showed the presence of 6 of the 7 virulence determinants described in the TW14359 O157 strain associated with the raw spinach outbreak in the U.S. in 2006. More than 80% of bovine strains showed the presence of 3 of these factors. The q933 allele, which has been related to high toxin production, was present in 98.2% of clinical strains and 75.9% of the bovine isolates. The molecular characterization of human STEC O157 strains allows us to conclude that the particular situation previously described for Neuquén Province, may actually be a characteristic of the whole country. These genetic features are quite similar to those observed in the bovine reservoir and may be derived from it. This data confirms that, unlike the rest of the world, in Argentina most of the STEC O157 strains present in cattle may cause human infections of varying severity and the marked virulence described for these strains may be related to the high incidence of HUS in our country.

The Epinephrine/Norepinephrine/Autoinducer-3 Interkingdom Signaling System in Escherichia coli O157:H7

Epinephrine/norepinephrine/AI-3 signaling is used as an interkingdom chemical signaling system between microbes and their hosts. This system is also exploited by pathogens to regulate virulence traits. In enterohemorrhagic E. coli (EHEC) O157:H7, it is essential for pathogenesis and flagella motility. These three signals activate expression of a pathogenicity island named locus of enterocyte effacement (LEE), Shiga toxin, and the flagella regulon. These signals are sensed by the two-component system QseBC, whereas the bacterial membrane receptor QseC autophosphorylates and phosphorylates the QseB response regulator initiating a complex phosphorelay signaling cascade that activates the expression of a second two-component system, QseEF. The QseEF two-component system is also involved in the expression of the virulence genes, and it senses epinephrine, phosphate, and sulfate. This complex signaling cascade still needs to be completely elucidated.

Shiga Toxins: Potent Poisons, Pathogenicity Determinants, and Pharmacological Agents

The Shiga toxins (Stxs), also known as Vero toxins and previously called Shiga-like toxins, are a family of potent protein synthesis inhibitors made by Shigella dysenteriae type 1 and some serogroups of Escherichia coli that cause bloody diarrhea in humans. Stxs act as virulence factors for both S. dysenteriae and E. coli and contribute to the disease process initiated by those organisms both directly and indirectly. A handful of methods exist for toxin purification, and the toxins can now even be purchased commercially. However, the Stxs are now classified as select agents, and specific rules govern the distribution of both the toxin and clones of the toxin. Toxin delivery into the host in S. dysenteriae type 1 is most likely aided by the invasiveness of that organism. Although the Stxs are made and produced by bacteria, they do not appear to act against either their host organism or other bacteria under normal circumstances, most likely because the A subunit is secreted from the cytoplasm as soon as it is synthesized and because the holotoxin cannot enter intact bacterial cells. The effectiveness of antibiotic therapy in patients infected with Stx-producing E. coli (STEC) such as O157:H7 as well as the potential risks of such treatment are areas of controversy. Several studies indicate that the course of the diarrhea stage of the disease is unaltered by antibiotic treatment. Several groups anticipate that a therapy that targets the Stxs is an important component of trying to alleviate disease caused by Stx-producing bacteria.

Molecular characterization and antibiotic susceptibility pattern of caprine Shiga toxin producing-Escherichia coli (STEC) isolates from India

The present study was conducted to detect the occurrence, serotype, genotype, phylogenetic relationship and antimicrobial resistance pattern of STEC from healthy goats of West Bengal, India. From the 125 faecal samples collected from healthy goats, 245 isolates were identified as Escherichia coli. The E. coli harbouring any gene for Shiga toxins (stx 1/stx 2) was detected in 36 (14.7%) of the 245 E. coli isolates. These STEC strains belonged to 22 different serogroups (O2, O5, O20, O21, O22, O25, O41, O44, O45, O60, O71, O76, O84, O85, O87, O91, O103, O112, O113, O120, O156, and O158) and three were untypeable. The stx 1 and stx 2 was detected in 26 (72.2%) and 21 (58.3%) of Shiga toxin producing-E. coli (STEC) isolates, respectively. Further, E. coli harbouring eaeA only (Enteropathogenic E. coli) and ehxA was detected in 22 (61.1%) and 28 (77.7%) isolates, respectively. Whereas the saa was present in 8 (22.2%) E. coli isolates. The subtyping of the 26 E. coli strains possessing stx 1 showed that 73.% (19/26) of these isolates were positive for stx 1C subtype. Of the 21 isolates with the stx 2 gene, 42.8% (9/21) were positive for stx 2C, and 38.1% (8/21) were positive for stx 2d gene. The phylogenetic analysis of STEC strains after RAPD reveals eight major clusters. However, no serogroup specific cluster was observed. Resistance was observed most frequently to erythromycin (80.5%), amikacin (52.7%), cephalothin (50%), kanamycin (41.6%), neomycin (36.1%) and gentamycin (36.1%) and less frequently to norfloxacin (2.7%), enrofloxacin (2.7%), and ciprofloxacin (2.7%). Multidrug resistance was observed in eleven STEC isolates.

Characterization of farm, food, and clinical Shiga toxin-producing Escherichia coli (STEC) O113

Thirty-nine Shiga toxin-producing Escherichia coli (STEC) O113 Irish farm, abattoir, and clinical isolates were analyzed in conjunction with eight Australian, New Zealand, and Norwegian strains for H (flagellar) antigens, virulence gene profile (eaeA, hlyA, tir, espA, espB katP, espP, etpD, saa, sab, toxB, iha, lpfA(O157/OI-141,) lpfA(O113,) and lpfA(O157/OI-154)), Shiga toxin gene variants (stx(1c), stx(1d), stx(2), stx(2c), stx(2dact), stx(2e), stx(2f,) and stx(2g)) and were genotyped using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). All of the Irish strains were O113:H4, regardless of source, while all non-Irish isolates carried the H21 flagellar antigen. The stx(1) gene was present in 30 O113:H4 strains only, whereas the stx(2d) gene was common to all isolates regardless of source. In contrast, eaeA was absent, while hlyA was found in the Australian, New Zealand, Norwegian, and two of the Irish human clinical isolates. saa was present in the O113:H21 but not in the O113:H4 serotype. To the best of the author's knowledge, this is the first report of clinically significant STEC lacking both the eaeA and saa genes. PFGE analysis was inconclusive; however, MLST grouped the strains into three sequence types (ST): ST10, ST56, and ST223. Based on our findings, it was concluded that the stx(2d) gene is common in STEC O113, which are generally eaeA negative. Furthermore, STEC O113:H4 is a new, emerging bovine serotype of human clinical significance.

Shiga Toxin (Stx) Classification, Structure, and Function

Shiga toxin (Stx) is one of the most potent bacterial toxins known. Stx is found in Shigella dysenteriae 1 and in some serogroups of Escherichia coli (called Stx1 in E. coli). In addition to or instead of Stx1, some E. coli strains produce a second type of Stx, Stx2, that has the same mode of action as Stx/Stx1 but is antigenically distinct. Because subtypes of each toxin have been identified, the prototype toxin for each group is now designated Stx1a or Stx2a. The Stxs consist of two major subunits, an A subunit that joins noncovalently to a pentamer of five identical B subunits. The A subunit of the toxin injures the eukaryotic ribosome and halts protein synthesis in target cells. The function of the B pentamer is to bind to the cellular receptor, globotriaosylceramide, Gb3, found primarily on endothelial cells. The Stxs traffic in a retrograde manner within the cell, such that the A subunit of the toxin reaches the cytosol only after the toxin moves from the endosome to the Golgi and then to the endoplasmic reticulum. In humans infected with Stx-producing E. coli, the most serious manifestation of the disease, hemolytic-uremic syndrome, is more often associated with strains that produce Stx2a rather than Stx1a, and that relative toxicity is replicated in mice and baboons. Stx1a and Stx2a also exhibit differences in cytotoxicity to various cell types, bind dissimilarly to receptor analogs or mimics, induce differential chemokine responses, and have several distinctive structural characteristics.

Sheep as an important source of E. coli O157/O157:H7 in Turkey

Escherichia coli O157:H7 is a globally important foodborne pathogen and has been mainly associated with cattle as the reservoir. However, accumulating data shows the importance of sheep as an E. coli O157:H7 vehicle. The presence of E. coli O157/O157:H7 in recto-anal mucosal swap and carcass sponge samples of 100 sheep brought to the slaughterhouse in Kirikkale were analyzed over a year. Molecular characteristics (stx1, stx2, eaeA, hly, lpfA1-3, espA, eae-α1, eae-α2, eae-β, eae-β1, eae-β2, eae-γ1, eae-γ2/θ, stx1c, stx1d, stx2c, stx2d, stx2e, stx2f, stx2g, blaampC, tet(A), tet(B), tet(C), tet(D), tet(E), tet(G), sul1, sul2, floR, cmlA, strA, strB and aadA) of 79 isolates were determined and minimum inhibitory concentrations of 20 different antibiotics were investigated. E. coli O157/O157:H7 was found in 18% of sheep included in the study and was more prevalent in yearlings than lambs and mature sheep, and male than female sheep, though none of the categories (season, sex or age range) had significant effect on prevalence. Furthermore, Shiga-toxigenic E. coli (STEC) O157:H7 was determined in 2% and 8% of sheep feces and carcasses, respectively. Additionally, lpfA1-3 and eae-γ1 were detected in all isolates. None of the isolates showed resistance against investigated antibiotics, even though 4 sorbitol fermenting E. coli O157 isolates were positive for tet(A), sul1 and aadA. This is the first study in Turkey that reveals the potential public health risk due to the contamination of sheep carcasses with potentially highly pathogenic STEC O157:H7 strains.

Genotypic characterization of Escherichia coli O157:H7 strains that cause diarrhea and hemolytic uremic syndrome in Neuquén, Argentina

Shiga toxin-producing Escherichia coli (STEC) are important food-borne pathogens associated with cases of diarrhea, hemorrhagic colitis and hemolytic uremic syndrome (HUS). E. coli O157:H7 is the dominant serotype in Argentina and also in Neuquén Province, in which HUS incidence is above the national average, with a maximum of 28.6 cases per 100,000 children less than 5 years old reported in 1998. The aim of this study was to characterize a collection of 70 STEC O157 strains isolated from patients with diarrhea and HUS treated in the province of Neuquén, Argentina, between 1998 and 2011. All strains harbored eae, ehxA, rfbO157, and fliCH7 genes, and stx2a/stx2c (78.7%) was the predominant genotype. A total of 64 (91.4%) STEC O157 strains belonged to the hypervirulent clade 8 tested using both 4 and 32 SNP typing schemes. The strains showed the highest values reported in the literature for 6 of the 7 virulence determinants described in the TW14359 O157 strain associated with the raw spinach outbreak in the U.S. in 2006. Clade 8 strains were strongly associated with two of them: ECSP_3286, factor encoding an outer membrane protein that facilitates the transport of the heme complex (P=0.001), and in particular extracellular factor ECSP_2870/2872, coding proteins related to adaptation to plant hosts (P=0.000004). The q933 allele, which has been related to high toxin production, was present in 97.1% of the strains studied for the anti-terminator Q gene. In summary, this study describes, for the first time in Argentina, the almost exclusive circulation of strains belonging to the hypervirulent clade 8, and also the presence of putative virulence factors in higher frequencies than those reported worldwide. These data may help to understand the causes of the particular epidemiological situation related to HUS in Neuquén Province.

stx2vhaIs the Dominant Genotype of Shiga Toxin-ProducingEscherichia coliO157:H7 Isolated from Patients and Domestic Animals in Three Regions of China

Shiga toxin-producing Escherichia coli(STEC) O157: H7 strains were isolated from domestic animals and patients from Xuzhou City, Jiangsu Province, China and the bordering Anhui and Henan Provinces and were examined for the stx genotype. Of 390 strains, 277 were identified as genotype stx2vha ; 41, stx2 ; 51, stx2-stx1 ; 1, stx2-stx2vha-stx1 ; 5, stx2-stx2vha ; and 15 were un-typeable. Of the 277 stx2vha-bearing isolates, 116 were isolated from goats; 42, cattle; 38, hens, and 35 from pigs. The study shows stx2vha is the dominant genotype and goats are an important reservoir.

Prevalence of Farm and Slaughterhouse Workers Carrying Shiga Toxin-Producing Escherichia coli in Korea

OBJECTIVES

The aim of this study was to investigate the distribution of Shiga toxin (Stx) gene-positive stool samples from dairy farmer and slaughterhouse workers in Gyeonggi-Do province.

METHODS

A total of 621 samples from healthy farmers and 198 samples from slaughterhouse workers were screened by polymerase chain reaction (PCR) for Shiga toxigenic Escherichia coli (STEC) infection on stool samples.

RESULTS

The PCR product of Stx-encoding genes was detected in 21 (3.4%) of 621 farmers and 15 (7.6%) of 198 slaughterhouse workers' stool samples. Distribution of the Stx PCR positive workers by age increment revealed an increase in STEC infection with age increment in both workers. Distribution of the Stx PCR positive workers by working years revealed an increase in STEC infection with working years in farmers.

CONCLUSION

These results of the study show that slaughterhouse workers are at higher risk of STEC infection than farmers. In addition, slaughterhouse workers have a more potential source of food contamination of STEC and transmission.

Isolation, molecular characterization and antibiotic resistance of Shiga Toxin-Producing Escherichia coli (STEC) from buffalo in India

In total, 363 Escherichia coli were isolated from 165 faecal samples of healthy buffaloes in West Bengal, India. Twenty-four of these isolates (6·61%) were found to carry at least one gene characteristic for Shiga toxin-producing Escherichia coli (STEC). These STEC strains belonged to 13 different O-serogroups. The stx1 gene was present in 23 (95·8%) of total STEC isolates, whereas 20 (83·3%) STEC isolates carried the gene stx2. Twelve strains of E. coli (50% of total STEC isolates) possessed enterohaemolysin (ehxA) gene in combination with others. Fourteen (58·33%) isolates found to possess saa gene. However, no E. coli was detected harbouring gene for intimin protein (eaeA). Of 23 stx1 -positive isolates, seven (30·43%) were positive for genes of the stx1C subtype. Of the 20 isolates with the stx2 gene, 25% (5/20) possessed stx2C and 10% (2/20) possessed stx2d gene. The phylogenetic analysis after RAPD of STEC strains revealed six major clusters. The isolated STEC strains were resistant most frequently to erythromycin (95·83%), cephalothin (62·5%), amikacin (54·17%), kanamycin (45·83%) and gentamicin (41·67%) group of antibiotics. No ESBL-producing (blaCTXM , blaTEM , blaSHV ) or quinolone resistance gene (qnrA) was detected in the STEC isolates.

Evolution of the Stx2-encoding prophage in persistent bovine Escherichia coli O157:H7 strains

Escherichia coli O157:H7 is a human pathogen that resides asymptomatically in its bovine host. The level of Shiga toxin (Stx) produced is variable in bovine-derived strains in contrast to human isolates that mostly produce high levels of Stx. To understand the genetic basis for varied Stx production, chronological collections of bovine isolates from Wisconsin dairy farms, R and X, were analyzed for multilocus prophage polymorphisms, stx(2) subtypes, and the levels of stx(2) transcript and toxin. The E. coli O157:H7 that persisted on both farms were phylogenetically distinct and yet produced little to no Stx2 due to gene deletions in Stx2c-encoding prophage (farm R) or insertional inactivation of stx(2a) by IS1203v (farm X). Loss of key regulatory and lysis genes in Stx2c-encoding prophage abolished stx(2c) transcription and induction of the prophage and stx(2a)::IS1203v in Stx2a-encoding prophage generated a truncated stx(2a) mRNA without affecting phage production. Stx2-producing strains were transiently present (farm R) and became Stx2 negative on farm X (i.e., stx(2a)::IS1203v). To our knowledge, this is the first study that details the evolution of E. coli O157:H7 and its Stx2-encoding prophage in a chronological collection of natural isolates. The data suggest the bovine and farm environments can be niches where Stx2-negative E. coli O157:H7 emerge and persist, which explains the Stx variability in bovine isolates and may be part of an evolutionary step toward becoming bovine specialists.

Comparative genomics and stx phage characterization of LEE-negative Shiga toxin-producing Escherichia coli

Infection by Escherichia coli and Shigella species are among the leading causes of death due to diarrheal disease in the world. Shiga toxin-producing E. coli (STEC) that do not encode the locus of enterocyte effacement (LEE-negative STEC) often possess Shiga toxin gene variants and have been isolated from humans and a variety of animal sources. In this study, we compare the genomes of nine LEE-negative STEC harboring various stx alleles with four complete reference LEE-positive STEC isolates. Compared to a representative collection of prototype E. coli and Shigella isolates representing each of the pathotypes, the whole genome phylogeny demonstrated that these isolates are diverse. Whole genome comparative analysis of the 13 genomes revealed that in addition to the absence of the LEE pathogenicity island, phage-encoded genes including non-LEE encoded effectors, were absent from all nine LEE-negative STEC genomes. Several plasmid-encoded virulence factors reportedly identified in LEE-negative STEC isolates were identified in only a subset of the nine LEE-negative isolates further confirming the diversity of this group. In combination with whole genome analysis, we characterized the lambdoid phages harboring the various stx alleles and determined their genomic insertion sites. Although the integrase gene sequence corresponded with genomic location, it was not correlated with stx variant, further highlighting the mosaic nature of these phages. The transcription of these phages in different genomic backgrounds was examined. Expression of the Shiga toxin genes, stx(1) and/or stx(2), as well as the Q genes, were examined with quantitative reverse transcriptase polymerase chain reaction assays. A wide range of basal and induced toxin induction was observed. Overall, this is a first significant foray into the genome space of this unexplored group of emerging and divergent pathogens.

Detection of Shiga toxin variants among Shiga toxin-forming Escherichia coli isolates from animal stool, meat and human stool samples in India

AIM

To study the prevalence and distribution of various variants in the stx gene of Shiga toxin-producing Escherichia coli (STEC) isolated from diverse environmental sources (animal stool, meat) and human illness, from a large geographic area in India, and to understand the association between variants, serotype distribution and human disease.

METHODS AND RESULTS

A surveillance for STEC was conducted in the semi-urban and rural areas of Punjab, Himachal, Haryana and Chandigarh. Shiga toxin-producing Escherichia coli isolates (80 animal stool, 39 meat, 21 human stool from diarrhoea and HUS cases) were characterized for stx variants by PCR. Shiga-like toxin (Stx) was detected using Ridascreen-EIA assay. Variant stx2c was the most common (25·1%), followed by stx1d (13%), stx1c (10·7%) and stx2d (9·2%), whereas stx2e, stx2f and stx2g were absent. Only 8/21 (38%) human isolates harboured stx variants, of which stx2c and stx2d were found in 2 and 1 isolates, respectively. The low frequency of carriage of these potentially more pathogenic variants may explain the low severity of human illness seen in India. Shiga-like toxin was detected in only 42 of the isolates positive for the stx genes probably due to the low levels of toxins produced. Serogroup distribution was found to be diverse, suggesting the lack of any predominant circulating type.

CONCLUSIONS

The presence of stx variants 1c, 1d, 2c and stx2d in diverse environmental and human sources in India was demonstrated. The prevalence of the most common subtype stx2c found in this study in animal isolates may pose a threat to the public health. We report the subtyping of human STEC isolates and report the presence of stx1d subtype for the first time from India.

SIGNIFICANCE AND IMPACT OF THE STUDY

We demonstrated the presence of potentially pathogenic subtypes in the environmental specimens which may act as a reservoir for human infections. Serogroups new to India were also reported.

Haemolytic uraemic syndrome in India due to Shiga toxigenic Escherichia coli

The emergence of Shiga toxigenic Escherichia coli (STEC) as a causative agent of diarrhoea, haemorrhagic colitis and haemolytic uraemic syndrome (HUS) in humans is a significant public health concern worldwide. Here we describe a case of HUS following dysentery due to STEC. Though STEC is not a major cause of diarrhoea in India, we recommend that STEC should be looked for in all cases of bloody diarrhoea. To our knowledge, this is the first case of HUS caused by STEC in India.

Escherichia coli: a brief review of diarrheagenic pathotypes and their role in diarrheal diseases in Iran

Diarrheagenic Escherichia coli have developed different strategies for establishment of infection in their host. Understanding these pathogenic mechanisms has led to the development of specific diagnostic tools for identification and categorization of E. coli strains into different pathotypes. This review aims to provide an overview of the various categories of diarrheagenic Escherichia coli and the data obtained in Iran pertaining to these pathotypes.

Shiga toxins

Shiga toxins are virulence factors produced by the bacteria Shigella dysenteriae and certain strains of Escherichia coli. There is currently no available treatment for disease caused by these toxin-producing bacteria, and understanding the biology of the Shiga toxins might be instrumental in addressing this issue. In target cells, the toxins efficiently inhibit protein synthesis by inactivating ribosomes, and they may induce signaling leading to apoptosis. To reach their cytoplasmic target, Shiga toxins are endocytosed and transported by a retrograde pathway to the endoplasmic reticulum, before the enzymatically active moiety is translocated to the cytosol. The toxins thereby serve as powerful tools to investigate mechanisms of intracellular transport. Although Shiga toxins are a serious threat to human health, the toxins may be exploited for medical purposes such as cancer therapy or imaging.

Shiga toxin-producing Escherichia coli serotype O78:H(-) in family, Finland, 2009

STEC carrying stx_1c and hlyA genes can invade the human bloodstream.

Shiga toxin–producing Escherichia coli (STEC) is a pathogen that causes gastroenteritis and bloody diarrhea but can lead to severe disease, such as hemolytic uremic syndrome (HUS). STEC serotype O78:H^– is rare among humans, and infections are often asymptomatic. We detected a sorbitol-fermenting STEC O78:H^–stx_1c:hlyA in blood and fecal samples of a 2-week-old boy who had bacteremia and HUS and in fecal samples of his asymptomatic family members. The phenotypic and genotypic characteristics and the virulence properties of this invasive STEC were investigated. Our findings demonstrate that contrary to earlier suggestions, STEC under certain conditions can invade the human bloodstream. Moreover, this study highlights the need to implement appropriate diagnostic methods for identifying the whole spectrum of STEC strains associated with HUS.

Multicenter evaluation of a sequence-based protocol for subtyping Shiga toxins and standardizing Stx nomenclature

When Shiga toxin-producing Escherichia coli (STEC) strains emerged as agents of human disease, two types of toxin were identified: Shiga toxin type 1 (Stx1) (almost identical to Shiga toxin produced by Shigella dysenteriae type 1) and the immunologically distinct type 2 (Stx2). Subsequently, numerous STEC strains have been characterized that express toxins with variations in amino acid sequence, some of which confer unique biological properties. These variants were grouped within the Stx1 or Stx2 type and often assigned names to indicate that they were not identical in sequence or phenotype to the main Stx1 or Stx2 type. A lack of specificity or consistency in toxin nomenclature has led to much confusion in the characterization of STEC strains. Because serious outcomes of infection have been attributed to certain Stx subtypes and less so with others, we sought to better define the toxin subtypes within the main Stx1 and Stx2 types. We compared the levels of relatedness of 285 valid sequence variants of Stx1 and Stx2 and identified common sequences characteristic of each of three Stx/Stx1 and seven Stx2 subtypes. A novel, simple PCR subtyping method was developed, independently tested on a battery of 48 prototypic STEC strains, and improved at six clinical and research centers to test the reproducibility, sensitivity, and specificity of the PCR. Using a consistent schema for nomenclature of the Stx toxins and stx genes by phylogenetic sequence-based relatedness of the holotoxin proteins, we developed a typing approach that should obviate the need to bioassay each newly described toxin and that predicts important biological characteristics.

Serotypes and virulotypes of non-O157 shiga-toxin producing Escherichia coli (STEC) on bovine hides and carcasses

Four hundred and fifty beef animal hides and a similar number of carcasses were screened for STEC in 3 beef abattoirs over a 12 month period using PCR and culture based methods. 67% (301/450) of hides and 27% (122/450) of carcasses were STEC PCR positive. Forty isolates representing 12 STEC serotypes (O5:H-, O13:H2, O26:H11, O33:H11, O55:H11, O113:H4, O128:H8, O136:H12, O138:H48, O150:H2, O168:H8 and ONT:H11) and 15 serotype-virulotype combinations were identified. This study provides much needed non-O157 STEC surveillance data and also provides further evidence of bovines as a source of clinically significant STEC as well as identifying 3 emerging serotypes O5:H- (eae-β1), O13:H2 (eae-ζ), and O150:H2 (eae-ζ) that should be considered when developing beef testing procedures for non-O157 STEC.

Identification of genes expressed in cultures of E. coli lysogens carrying the Shiga toxin-encoding prophage Φ24B

BACKGROUND

Shigatoxigenic E. coli are a global and emerging health concern. Shiga toxin, Stx, is encoded on the genome of temperate, lambdoid Stx phages. Genes essential for phage maintenance and replication are encoded on approximately 50% of the genome, while most of the remaining genes are of unknown function nor is it known if these annotated hypothetical genes are even expressed. It is hypothesized that many of the latter have been maintained due to positive selection pressure, and that some, expressed in the lysogen host, have a role in pathogenicity. This study used Change Mediated Antigen Technology (CMAT)™ and 2D-PAGE, in combination with RT-qPCR, to identify Stx phage genes that are expressed in E. coli during the lysogenic cycle.

RESULTS

Lysogen cultures propagated for 5-6 hours produced a high cell density with a low proportion of spontaneous prophage induction events. The expression of 26 phage genes was detected in these cultures by differential 2D-PAGE of expressed proteins and CMAT. Detailed analyses of 10 of these genes revealed that three were unequivocally expressed in the lysogen, two expressed from a known lysogenic cycle promoter and one uncoupled from the phage regulatory network.

CONCLUSION

Propagation of a lysogen culture in which no cells at all are undergoing spontaneous lysis is impossible. To overcome this, RT-qPCR was used to determine gene expression profiles associated with the growth phase of lysogens. This enabled the definitive identification of three lambdoid Stx phage genes that are expressed in the lysogen and seven that are expressed during lysis. Conservation of these genes in this phage genome, and other Stx phages where they have been identified as present, indicates their importance in the phage/lysogen life cycle, with possible implications for the biology and pathogenicity of the bacterial host.

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.