Outbreaks of virulent diarrheagenic Escherichia coli--are we in control?

Molecular epidemiology and antimicrobial susceptibility of diarrheagenic Escherichia coli isolated from children under age five with and without diarrhea in Central Ethiopia

BACKGROUND

Diarrhea is a serious health problem in children, with the highest mortality rate in sub-Saharan Africa. Diarrheagenic Escherichia coli (DEC) is among the major bacterial causes of diarrhea in children under age five. The present study aims to determine molecular epidemiology and antimicrobial resistance profiles of DEC and identify contributing factors for acquisition among children under age five in Central Ethiopia.

METHODS

A health facility-centered cross-sectional study was conducted in Addis Ababa and Debre Berhan, Ethiopia, from December 2020 to August 2021. A total of 476 specimens, 391 from diarrheic and 85 from non-diarrheic children under age five were collected. Bacterial isolation and identification, antimicrobial susceptibility, and pathotype determination using polymerase chain reaction (PCR) were done.

RESULTS

Of the 476 specimens analyzed, 89.9% (428/476) were positive for E. coli, of which 183 were positive for one or more genes coding DEC pathotypes. The overall prevalence of the DEC pathotype was 38.2% (183/476). The predominant DEC pathotype was enteroaggregative E. coli (EAEC) (41.5%, 76/183), followed by enterotoxigenic E. coli (21.3%, 39/183), enteropathogenic E. coli (15.3%, 28/183), enteroinvasive E. coli (12.6%, 23/183), hybrid strains (7.1%, 13/183), Shiga toxin-producing E. coli (1.6%, 3/183), and diffusely-adherent E. coli (0.6%, 1/183). DEC was detected in 40.7% (159/391) of diarrheic and 28.2% (24/85) in non-diarrheic children (p = 0.020). The majority of the DEC pathotypes were resistant to ampicillin (95.1%, 174/183) and tetracycline (91.3%, 167/183). A higher rate of resistance to trimethoprim-sulfamethoxazole (58%, 44/76), ciprofloxacin (22%, 17/76), ceftazidime and cefotaxime (20%, 15/76) was seen among EAEC pathotypes. Multidrug resistance (MDR) was detected in 43.2% (79/183) of the pathotypes, whereas extended spectrum ß-lactamase and carbapenemase producers were 16.4% (30/183) and 2.2% (4/183), respectively.

CONCLUSION

All six common DEC pathotypes that have the potential to cause severe diarrheal outbreaks were found in children in the study area; the dominant one being EAEC with a high rate of MDR.

O-Antigen Diversification Masks Identification of Highly Pathogenic Shiga Toxin-Producing Escherichia coli O104:H4-Like Strains

Shiga toxin-producing Escherichia coli (STEC) can give rise to a range of clinical outcomes from diarrhea to the life-threatening systemic condition hemolytic-uremic syndrome (HUS). Although STEC O157:H7 is the serotype most frequently associated with HUS, a major outbreak of HUS occurred in 2011 in Germany and was caused by a rare serotype, STEC O104:H4. Prior to 2011 and since the outbreak, STEC O104:H4 strains have only rarely been associated with human infections. From 2012 to 2020, intensified STEC surveillance was performed in Germany where the subtyping of ~8,000 clinical isolates by molecular methods, including whole-genome sequencing, was carried out. A rare STEC serotype, O181:H4, associated with HUS was identified, and like the STEC O104:H4 outbreak strain, this strain belongs to sequence type 678 (ST678). Genomic and virulence comparisons revealed that the two strains are phylogenetically related and differ principally in the gene cluster encoding their respective lipopolysaccharide O-antigens but exhibit similar virulence phenotypes. In addition, five other serotypes belonging to ST678 from human clinical infection, such as OX13:H4, O127:H4, OgN-RKI9:H4, O131:H4, and O69:H4, were identified from diverse locations worldwide. IMPORTANCE Our data suggest that the high-virulence ensemble of the STEC O104:H4 outbreak strain remains a global threat because genomically similar strains cause disease worldwide but that the horizontal acquisition of O-antigen gene clusters has diversified the O-antigens of strains belonging to ST678. Thus, the identification of these highly pathogenic strains is masked by diverse and rare O-antigens, thereby confounding the interpretation of their potential risk.

Bacteriophages to control Shiga toxin-producing E. coli - safety and regulatory challenges

Shiga toxin-producing Escherichia coli (STEC) are usually found on food products due to contamination from the fecal origin, as their main environmental reservoir is considered to be the gut of ruminants. While this pathogen is far from the incidence of other well-known foodborne bacteria, the severity of STEC infections in humans has triggered global concerns as far as its incidence and control are concerned. Major control strategies for foodborne pathogens in food-related settings usually involve traditional sterilization/disinfection techniques. However, there is an increasing need for the development of further strategies to enhance the antimicrobial outcome, either on food-contact surfaces or directly in food matrices. Phages are considered to be a good alternative to control foodborne pathogens, with some phage-based products already cleared by the Food and Drug Administration (FDA) to be used in the food industry. In European countries, phage-based food decontaminants have already been used. Nevertheless, its broad use in the European Union is not yet possible due to the lack of specific guidelines for the approval of these products. Furthermore, some safety concerns remain to be addressed so that the regulatory requirements can be met. In this review, we present an overview of the main virulence factors of STEC and introduce phages as promising biocontrol agents for STEC control. We further present the regulatory constraints on the approval of phages for food applications and discuss safety concerns that are still impairing their use.

Identification of Novel Biomarkers for Priority Serotypes of Shiga Toxin-Producing Escherichia coli and the Development of Multiplex PCR for Their Detection

It would be desirable to have an unambiguous scheme for the typing of Shiga toxin-producing Escherichia coli (STEC) isolates to subpopulations. Such a scheme should take the high genomic plasticity of E. coli into account and utilize the stratification of STEC into subgroups, based on serotype or phylogeny. Therefore, our goal was to identify specific marker combinations for improved classification of STEC subtypes. We developed and evaluated two bioinformatic pipelines for genomic marker identification from larger sets of bacterial genome sequences. Pipeline A performed all-against-all BLASTp analyses of gene products predicted in STEC genome test sets against a set of control genomes. Pipeline B identified STEC marker genes by comparing the STEC core proteome and the "pan proteome" of a non-STEC control group. Both pipelines defined an overlapping, but not identical set of discriminative markers for different STEC subgroups. Differential marker prediction resulted from differences in genome assembly, ORF finding and inclusion cut-offs in both workflows. Based on the output of the pipelines, we defined new specific markers for STEC serogroups and phylogenetic groups frequently associated with outbreaks and cases of foodborne illnesses. These included STEC serogroups O157, O26, O45, O103, O111, O121, and O145, Shiga toxin-positive enteroaggregative E. coli O104:H4, and HUS-associated sequence type (ST)306. We evaluated these STEC marker genes for their presence in whole genome sequence data sets. Based on the identified discriminative markers, we developed a multiplex PCR (mPCR) approach for detection and typing of the targeted STEC. The specificity of the mPCR primer pairs was verified using well-defined clinical STEC isolates as well as isolates from the ECOR, DEC, and HUSEC collections. The application of the STEC mPCR for food analysis was tested with inoculated milk. In summary, we evaluated two different strategies to screen large genome sequence data sets for discriminative markers and implemented novel marker genes found in this genome-wide approach into a DNA-based typing tool for STEC that can be used for the characterization of STEC from clinical and food samples.

Borosilicate Glass Fiber-Optic Biosensor for the Detection of Escherichia coli

Polyclonal antibodies against Escherichia coli and fluorescent, secondary, antibodies were immobilized on borosilicate glass fibers pre-treated with 3-glycidyloxypropyl trimethoxysilane (GPS). Light with an average wavelength of 627 nm, emitted by a diode placed at one end of the glass fiber, was detected by an ultrasensitive photodiode with peak sensitivity at 640 nm. Changes in fluorescence, caused by binding of E. coli to the antibodies, changed the net refractive index of the glass fiber and thus the internal reflection of light. These evanescent changes in photon energy were recorded by an ultrasensitive photodiode. Signals were amplified and changes in voltage recorded with a digital multimeter. A linear increase in voltage readings was recorded over 2 h when 3.0 × 10⁷ CFU/ml and 2.77 × 10⁹ CFU/ml E. coli were adhered to the antibodies. Voltage readings were recorded with E. coli cell numbers from 2 × 10³ CFU/ml to 2 × 10⁶ CFU/ml, but readings remained unchanged for 2 h, indicating that the limit of detection is 3.0 × 10⁷ CFU/ml. This simple technology may be used to develop a low-cost, portable, fiber-optic biosensor to detect E. coli in infections and may have applications in the medical field. Research is in progress to optimize the sensitivity of the fiber-optic biosensor and determine its specificity.

Isothiocyanates as effective agents against enterohemorrhagic Escherichia coli: insight to the mode of action

Production of Shiga toxins by enterohemorrhagic Escherichia coli (EHEC) which is responsible for the pathogenicity of these strains, is strictly correlated with induction of lambdoid bacteriophages present in the host's genome, replication of phage DNA and expression of stx genes. Antibiotic treatment of EHEC infection may lead to induction of prophage into a lytic development, thus increasing the risk of severe complications. This, together with the spread of multi-drug resistance, increases the need for novel antimicrobial agents. We report here that isothiocyanates (ITC), plant secondary metabolites, such as sulforaphane (SFN), allyl isothiocyanate (AITC), benzyl isothiocynanate (BITC), phenyl isothiocyanate (PITC) and isopropyl isothiocyanate (IPRITC), inhibit bacterial growth and lytic development of stx-harboring prophages. The mechanism underlying the antimicrobial effect of ITCs involves the induction of global bacterial stress regulatory system, the stringent response. Its alarmone, guanosine penta/tetraphosphate ((p)ppGpp) affects major cellular processes, including nucleic acids synthesis, which leads to the efficient inhibition of both, prophage induction and toxin synthesis, abolishing in this way EHEC virulence for human and simian cells. Thus, ITCs could be considered as potential therapeutic agents in EHEC infections.

Oxidative Stress in Shiga Toxin Production by Enterohemorrhagic Escherichia coli

Virulence of enterohemorrhagic Escherichia coli (EHEC) strains depends on production of Shiga toxins. These toxins are encoded in genomes of lambdoid bacteriophages (Shiga toxin-converting phages), present in EHEC cells as prophages. The genes coding for Shiga toxins are silent in lysogenic bacteria, and prophage induction is necessary for their efficient expression and toxin production. Under laboratory conditions, treatment with UV light or antibiotics interfering with DNA replication are commonly used to induce lambdoid prophages. Since such conditions are unlikely to occur in human intestine, various research groups searched for other factors or agents that might induce Shiga toxin-converting prophages. Among other conditions, it was reported that treatment with H₂O₂ caused induction of these prophages, though with efficiency significantly lower relative to UV-irradiation or mitomycin C treatment. A molecular mechanism of this phenomenon has been proposed. It appears that the oxidative stress represents natural conditions provoking induction of Shiga toxin-converting prophages as a consequence of H₂O₂ excretion by either neutrophils in infected humans or protist predators outside human body. Finally, the recently proposed biological role of Shiga toxin production is described in this paper, and the “bacterial altruism” and “Trojan Horse” hypotheses, which are connected to the oxidative stress, are discussed.

The Role of the Exo-Xis Region in Oxidative Stress-Mediated Induction of Shiga Toxin-Converting Prophages

Previous studies indicated that these genetic elements could be involved in the regulation of lysogenization and prophage induction processes. The effects were dramatic in Shiga toxin-converting phage Φ24(B) after treatment with oxidative stress-inducing agent, hydrogen peroxide, while they were less pronounced in bacteriophage λ and in both phages irradiated with UV. The hydrogen peroxide-caused prophage induction was found to be RecA-dependent. Importantly, in hydrogen peroxide-treated E. coli cells lysogenic for either λ or Φ24(B), deletion of the exo-xis region resulted in a significant decrease in the levels of expression of the S.O.S. regulon genes. Moreover, under these conditions, a dramatic decrease in the levels of expression of phage genes crucial for lytic development (particularly xis, exo, N, cro, O, Q, and R) could be observed in Φ24(B)-, but not in λ-bearing cells. We conclude that genes located in the exo-xis region are necessary for efficient expression of both host S.O.S regulon in lysogenic bacteria and regulatory genes of Shiga toxin-converting bacteriophage Φ24(B).

A simple and rapid procedure for the detection of genes encoding Shiga toxins and other specific DNA sequences

A novel procedure for the detection of specific DNA sequences has been developed. This procedure is based on the already known method employing PCR with appropriate primers and a sequence-specific DNA probe labeled with the fluorescent agent 6-carboxylfluorescein (FAM) at the 5′ end and the fluorescence quencher BHQ-1 (black hole quencher) at the 3′ end. However, instead of the detection of the fluorescence signal with the use of real-time PCR cyclers, fluorescence/luminescence spectrometers or fluorescence polarization readers, as in all previously-reported procedures, we propose visual observation of the fluorescence under UV light directly in the reaction tube. An example for the specific detection of the Shiga toxin-producing Escherichia coli (STEC) strains, by detecting Shiga toxin genes, is demonstrated. This method appears to be specific, simple, rapid and cost effective. It may be suitable for use in research laboratories, as well as in diagnostic units of medical institutions, even those equipped only with a thermocycler and a UV transilluminator, particularly if rapid identification of a pathogen is required.

UV-Sensitivity of Shiga Toxin-Converting Bacteriophage Virions Φ24B, 933W, P22, P27 and P32

Shiga toxin-converting bacteriophages (Stx phages) are present as prophages in Shiga toxin-producing Escherichia coli (STEC) strains. Theses phages can be transmitted to previously non-pathogenic E. coli cells making them potential producers of Shiga toxins, as they bear genes for these toxins in their genomes. Therefore, sensitivity of Stx phage virions to various conditions is important in both natural processes of spreading of these viruses and potential prophylactic control of appearance of novel pathogenic E. coli strains. In this report we provide evidence that virions of Stx phages are significantly more sensitive to UV irradiation than bacteriophage λ. Following UV irradiation of Stx virions at the dose of 50 J/m², their infectivity dropped by 1–3 log₁₀, depending on the kind of phage. Under these conditions, a considerable release of phage DNA from virions was observed, and electron microscopy analyses indicated a large proportion of partially damaged virions. Infection of E. coli cells with UV-irradiated Stx phages resulted in significantly decreased levels of expression of N and cro genes, crucial for lytic development. We conclude that inactivation of Stx virions caused by relatively low dose of UV light is due to damage of capsids that prevents effective infection of the host cells.

An Adjusted Likelihood Ratio Approach Analysing Distribution of Food Products to Assist the Investigation of Foodborne Outbreaks

In order to facilitate foodborne outbreak investigations there is a need to improve the methods for identifying the food products that should be sampled for laboratory analysis. The aim of this study was to examine the applicability of a likelihood ratio approach previously developed on simulated data, to real outbreak data. We used human case and food product distribution data from the Norwegian enterohaemorrhagic Escherichia coli outbreak in 2006. The approach was adjusted to include time, space smoothing and to handle missing or misclassified information. The performance of the adjusted likelihood ratio approach on the data originating from the HUS outbreak and control data indicates that the adjusted approach is promising and indicates that the adjusted approach could be a useful tool to assist and facilitate the investigation of food borne outbreaks in the future if good traceability are available and implemented in the distribution chain. However, the approach needs to be further validated on other outbreak data and also including other food products than meat products in order to make a more general conclusion of the applicability of the developed approach.

Genetic Diversity of the fliC Genes Encoding the Flagellar Antigen H19 of Escherichia coli and Application to the Specific Identification of Enterohemorrhagic E. coli O121:H19

Enterohemorrhagic Escherichia coli (EHEC) O121:H19 belong to a specific clonal type distinct from other classical EHEC and major enteropathogenic E. coli groups and is regarded as one of the major EHEC serogroups involved in severe infections in humans. Sequencing of the fliC genes associated with the flagellar antigen H19 (fliCH19) revealed the genetic diversity of the fliCH19 gene sequences in E. coli. A cluster analysis of 12 fliCH19 sequences, 4 from O121 and 8 from non-O121 E. coli strains, revealed five different genotypes. All O121:H19 strains fell into one cluster, whereas a second cluster was formed by five non-O121:H19 strains. Cluster 1 and cluster 2 strains differ by 27 single nucleotide exchanges in their fliCH19 genes (98.5% homology). Based on allele discrimination of the fliCH19 genes, a real-time PCR test was designed for specific identification of EHEC O121:H19. The O121 fliCH19 PCR tested negative in 73 E. coli H19 strains that belonged to serogroups other than O121, including 28 different O groups, O-nontypeable H19, and O-rough:H19 strains. The O121 fliCH19 PCR reacted with all 16 tested O121:H19 strains and 1 O-rough:H19 strain which was positive for the O121 wzx gene. A cross-reaction was observed only with E. coli H32 strains which share sequence similarities in the target region of the O121 fliCH19 PCR. The combined use of O-antigen genotyping (O121 wzx) and the detection of O121 fliCH19 allele type contributes to improving the identification and molecular serotyping of EHEC O121:H19 motile and nonmotile strains and variants of these strains lacking stx genes.

Genetic Relatedness Among Escherichia coli Pathotypes Isolated from Food Products for Human Consumption in Cartagena, Colombia

Foodborne pathogens are a leading cause of mild-to-severe gastrointestinal illnesses worldwide. Escherichia coli pathotypes have been known to cause gastrointestinal illnesses in children less than 5 years old in Colombia. However, insufficient information is available on the prevalence of E. coli contamination of food products and the kind of E. coli food product reservoirs. The two objectives of this study were designed to address this issue. The first objective was to ascertain coliform, E. coli, and pathogenic E. coli contamination of food products readily available for human consumption in Cartagena, Colombia. The second objective was to evaluate the relationship between pathogenic E. coli isolated from food products and those isolated from cases of diarrhea in children. Food product samples consisting of pasteurized milk, unpasteurized fruit juice, ground beef, cheese, and vegetables were obtained at four retail stores. The food samples were cultured in liquid media and tested for the presence of coliforms and E. coli. E. coli isolates were tested by polymerase chain reaction for the presence of pathogenic E. coli. Coliforms, E. coli, and E. coli intestinal pathotypes contamination were detected in 88.4%, 53%, and 2.1% of food product samples, respectively. Ground beef and cheese were the only food samples contaminated with E. coli intestinal pathotypes including enteropathogenic (EPEC), Shiga toxin-producing (STEC), and enterotoxigenic E. coli (ETEC). Closed multilocus sequencing typing relationships between diarrheagenic E. coli isolates from food products and from individuals with diarrhea suggest that food products readily available at public markets in Cartagena can transmit ETEC and possibly EPEC and STEC. We demonstrated that a high proportion of food products for human consumption available at public markets in Cartagena are contaminated with coliforms, E. coli, and E. coli intestinal pathogens. Furthermore, food products containing E. coli intestinal pathogens may be involved in the transmission of foodborne illnesses among children in Cartagena, Colombia.

Defects in RNA polyadenylation impair both lysogenization by and lytic development of Shiga toxin-converting bacteriophages

In Escherichia coli, the major poly(A) polymerase (PAP I) is encoded by the pcnB gene. In this report, a significant impairment of lysogenization by Shiga toxin-converting (Stx) bacteriophages (Φ24B, 933W, P22, P27 and P32) is demonstrated in host cells with a mutant pcnB gene. Moreover, lytic development of these phages after both infection and prophage induction was significantly less efficient in the pcnB mutant than in the WT host. The increase in DNA accumulation of the Stx phages was lower under conditions of defective RNA polyadenylation. Although shortly after prophage induction, the levels of mRNAs of most phage-borne early genes were higher in the pcnB mutant, at subsequent phases of the lytic development, a drastically decreased abundance of certain mRNAs, including those derived from the N, O and Q genes, was observed in PAP I-deficient cells. All of these effects observed in the pcnB cells were significantly more strongly pronounced in the Stx phages than in bacteriophage λ. Abundance of mRNA derived from the pcnB gene was drastically increased shortly (20 min) after prophage induction by mitomycin C and decreased after the next 20 min, while no such changes were observed in non-lysogenic cells treated with this antibiotic. This prophage induction-dependent transient increase in pcnB transcript may explain the polyadenylation-driven regulation of phage gene expression.

Lessons learned from a textbook outbreak: EHEC-O157:H7 infections associated with the consumption of raw meat products, June 2012, Limburg, Belgium

BACKGROUND

On 5 June 2012 several enterohemorrhagic Escherichia coli, EHEC, O157:H7 infections were reported to the public health authorities of Limburg.

METHODS

We performed a case-control study, a trace back/forward investigation and compared strains isolated from human cases and food samples. A case was defined as anyone with a laboratory-confirmed E. coli O157:H7-infection in North-East Limburg from May 30 2012 till July 15 2012. Family members with bloody diarrhea were also included as cases. E. coli O157 was isolated by culture and the presence of the virulence genes was verified using (q)PCR. Isolates were genotyped and compared by Pulsed Field Gel Electrophoresis (PFGE) and insertion sequence 629-printing (IS629-printing).

RESULTS

The outbreak involved 24 cases, of which 17 were laboratory-confirmed. Five cases developed Hemolytic Uremic Syndrome (HUS) and fifteen were hospitalized. Cases reported a significantly higher consumption of "steak tartare", a raw meat product (OR 48.12; 95% CI; 5.62- 416.01). Cases were also more likely to buy meat-products at certain butcheries (OR 11.67; 95% CI; 1.41 - 96.49). PFGE and IS629-printing demonstrated that the vtx1a vtx2a eae ehxA positive EHEC O157:H7 strains isolated from three meat products and all seventeen human stool samples were identical. In a slaughterhouse, identified by the trace-back investigation, a carcass infected with a different EHEC strain was found and confiscated.

CONCLUSION

We present a well described and effectively investigated foodborne outbreak associated with meat products. Our main recommendations are the facilitation and acceleration of the outbreak detection and the development of a communication plan to reaches all persons at risk.

MESH

Foodborne diseases, Shiga-toxigenic Escherichia coli, Enterohemorrhagic Escherichia coli, Meat products, Case control studies, Electrophoresis, Gel, Pulsed-Field.

Different expression patterns of genes from the exo-xis region of bacteriophage λ and Shiga toxin-converting bacteriophage Ф24B following infection or prophage induction in Escherichia coli

Lambdoid bacteriophages serve as useful models in microbiological and molecular studies on basic biological process. Moreover, this family of viruses plays an important role in pathogenesis of enterohemorrhagic Escherichia coli (EHEC) strains, as they are carriers of genes coding for Shiga toxins. Efficient expression of these genes requires lambdoid prophage induction and multiplication of the phage genome. Therefore, understanding the mechanisms regulating these processes appears essential for both basic knowledge and potential anti-EHEC applications. The exo-xis region, present in genomes of lambdoid bacteriophages, contains highly conserved genes of largely unknown functions. Recent report indicated that the Ea8.5 protein, encoded in this region, contains a newly discovered fused homeodomain/zinc-finger fold, suggesting its plausible regulatory role. Moreover, subsequent studies demonstrated that overexpression of the exo-xis region from a multicopy plasmid resulted in impaired lysogenization of E. coli and more effective induction of λ and Ф24_B prophages. In this report, we demonstrate that after prophage induction, the increase in phage DNA content in the host cells is more efficient in E. coli bearing additional copies of the exo-xis region, while survival rate of such bacteria is lower, which corroborated previous observations. Importantly, by using quantitative real-time reverse transcription PCR, we have determined patterns of expressions of particular genes from this region. Unexpectedly, in both phages λ and Ф24_B, these patterns were significantly different not only between conditions of the host cells infection by bacteriophages and prophage induction, but also between induction of prophages with various agents (mitomycin C and hydrogen peroxide). This may shed a new light on our understanding of regulation of lambdoid phage development, depending on the mode of lytic cycle initiation.

Escherichia coli O104:H4 outbreak in Germany--clarification of the origin of the epidemic

BACKGROUND

In 2011, Germany was hit by one of its largest outbreaks of acute gastroenteritis and haemolytic uraemic syndrome caused by a new emerging enterohaemorrhagic Escherichia coli O104:H4 strain. The German Haemolytic Uraemic Syndrome/Enterohaemorrhagic E. coli (GHUSEC) outbreak had unusual microbiological, infectiological and epidemiological features and its origin is still only partially solved. The aim of this article is to contribute to the clarification of the origin of the epidemic.

METHODS

To retrospectively assess whether the GHUSEC outbreak was natural, accidental or a deliberate one, we analysed it according to three published scoring and differentiation models. Data for application of these models were obtained by literature review in the database Medline for the period 2011-13.

RESULTS

The analysis of the unusual GHUSEC outbreak shows that the present official assumption of its natural origin is questionable and pointed out to a probability that the pathogen could have also been introduced accidentally or intentionally in the food chain.

CONCLUSION

The possibility of an accidental or deliberate epidemic should not be discarded. Further epidemiological, microbiological and forensic analyses are needed to clarify the GHUSEC outbreak.

Phenethyl isothiocyanate inhibits shiga toxin production in enterohemorrhagic Escherichia coli by stringent response induction

The pathogenicity of enterohemorrhagic Escherichia coli (EHEC) depends on production of Shiga toxins, which are encoded by stx genes located in the genomes of lambdoid prophages. Efficient expression of these genes requires prophage induction and lytic development of phages. Treatment of EHEC infections is problematic due to not only the resistance of various strains to antibiotics but also the fact that many antibiotics cause prophage induction, thus resulting in high-level expression of stx genes. Here we report that E. coli growth, Shiga toxin-converting phage development, and production of the toxin by EHEC are strongly inhibited by phenethyl isothiocyanate (PEITC). We demonstrate that PEITC induces the stringent response in E. coli that is mediated by massive production of a global regulator, guanosine tetraphosphate (ppGpp). The stringent response induction arises most probably from interactions of PEITC with amino acids and from amino acid deprivation-mediated activation of ppGpp synthesis. In mutants unable to synthesize ppGpp, development of Shiga toxin-converting phages and production of Shiga toxin are significantly enhanced. Therefore, ppGpp, which appears at high levels in bacterial cells after stimulation of its production by PEITC, is a negative regulator of EHEC virulence and at the same time efficiently inhibits bacterial growth. This is in contrast to stimulation of virulence of different bacteria by this nucleotide reported previously by others.

Pathogenicity, host responses and implications for management of enterohemorrhagic Escherichia coli O157:H7 infection

Enterohemorrhagic Escherichia coli serotype O157:H7 is a food- and waterborne pathogen that causes significant morbidity and mortality in both developing and industrialized nations. The present review focuses on the history, epidemiology and evolution of the pathogen; provides a mechanistic overview of major virulence factors (including Shiga toxins, locus of enterocyte effacement pathogenicity island and pO157 plasmid); discusses host immune responses to infection; considers available animal models; and provides an overview of current and potential future management considerations.

[The 2011 HUS epidemic in Germany. Challenges for disease control: what should be improved?]

From May to July 2011 [corrected] the world's largest outbreak of hemolytic uremic syndrome (HUS) occurred in northern Germany with dramatic consequences for the population, the health care system and the food industry. In the following we examine the detection of the outbreak, epidemic management and related public communication aspects based on scientific publications, media reports as well as own and new data analyses. The subsequent 17 recommendations concern issues such as participation in and implementation of existing and new surveillance systems particularly with respect to physicians, broad application of finely tuned microbiological typing, improved personnel capacity and crisis management structures within the public health service and evidence-based communication by administrations and scientific associations. Outbreaks of similar dimensions can inevitably occur again and result in costs which will far exceed investments needed for early detection and control. This societal balance should be taken into account in spite of limited resources in the public health sector.

Genes from the exo-xis region of λ and Shiga toxin-converting bacteriophages influence lysogenization and prophage induction

The exo–xis region, present in genomes of lambdoid bacteriophages, contains highly conserved genes of largely unknown functions. In this report, using bacteriophage λ and Shiga toxin-converting bacteriophage ϕ24_Β, we demonstrate that the presence of this region on a multicopy plasmid results in impaired lysogenization of Escherichia coli and delayed, while more effective, induction of prophages following stimulation by various agents (mitomycin C, hydrogen peroxide, UV irradiation). Spontaneous induction of λ and ϕ24_Β prophages was also more efficient in bacteria carrying additional copies of the corresponding exo–xis region on plasmids. No significant effects of an increased copy number of genes located between exo and xis on both efficiency of adsorption on the host cells and lytic development inside the host cell of these bacteriophages were found. We conclude that genes from the exo–xis region of lambdoid bacteriophages participate in the regulation of lysogenization and prophage maintenance.

Evaluation of seven different commercially available real-time PCR assays for detection of shiga toxin 1 and 2 gene subtypes

Following the recent outbreak of Shiga toxin-producing Escherichia coli (STEC) O104:H4 infection in Germany, the demand for fast detection of STEC has again increased. Various real-time PCR-based methods enabling detection of Shiga toxin genes (stx) have been developed and can be used for applications in food microbiology. The present study was conducted to evaluate the reliability of seven commercially available real-time PCR systems for detection of stx1 and stx2 subtypes. For this purpose, pure cultures of 18 STEC strains harboring all known stx1 and/or stx2 subtypes were tested. Only one of the seven real-time PCR systems detected all known stx1 and stx2 subtypes. Six systems failed to detect the stx2f subtype. One system missed stx2 subtypes reported in association with severe human disease. Because the presence of certain stx genes (subtypes) is considered an important indicator of STEC virulence, systems differentiating between the stx1 and stx2 gene groups provide added value. Reliable and fast detection of stx genes is of major importance for both diagnostic laboratories and the food industry.

Lysogenic conversion and phage resistance development in phage exposed Escherichia coli biofilms

In this study, three-day old mature biofilms of Escherichia coli were exposed once to either a temperate Shiga-toxin encoding phage (H-19B) or an obligatory lytic phage (T7), after which further dynamics in the biofilm were monitored. As such, it was found that a single dose of H-19B could rapidly lead to a near complete lysogenization of the biofilm, with a subsequent continuous release of infectious H-19B particles. On the other hand, a single dose of T7 rapidly led to resistance development in the biofilm population. Together, our data indicates a profound impact of phages on the dynamics within structured bacterial populations.

Altruism of Shiga toxin-producing Escherichia coli: recent hypothesis versus experimental results

Shiga toxin-producing Escherichia coli (STEC) may cause bloody diarrhea and hemorrhagic colitis (HC), with subsequent systemic disease. Since genes coding for Shiga toxins (stx genes) are located on lambdoid prophages, their effective production occurs only after prophage induction. Such induction and subsequent lytic development of Shiga toxin-converting bacteriophages results not only in production of toxic proteins, but also in the lysis (and thus, the death) of the host cell. Therefore, one may ask the question: what is the benefit for bacteria to produce the toxin if they die due to phage production and subsequent cell lysis? Recently, a hypothesis was proposed (simultaneously but independently by two research groups) that STEC may benefit from Shiga toxin production as a result of toxin-dependent killing of eukaryotic cells such as unicellular predators or human leukocytes. This hypothesis could make sense only if we assume that prophage induction (and production of the toxin) occurs only in a small fraction of bacterial cells, thus, a few members of the population are sacrificed for the benefit of the rest, providing an example of “bacterial altruism.” However, various reports indicating that the frequency of spontaneous induction of Shiga toxin-converting prophages is higher than that of other lambdoid prophages might seem to contradict the for-mentioned model. On the other hand, analysis of recently published results, discussed here, indicated that the efficiency of prophage excision under conditions that may likely occur in the natural habitat of STEC is sufficiently low to ensure survival of a large fraction of the bacterial host. A molecular mechanism by which partial prophage induction may occur is proposed. We conclude that the published data supports the proposed model of bacterial “altruism” where prophage induction occurs at a low enough frequency to render toxin production a positive selective force on the general STEC population.

Treatment of enterohemorrhagic Escherichia coli (EHEC) infection and hemolytic uremic syndrome (HUS)

Verotoxigenic Escherichia coli (VTEC) are a specialized group of E. coli that can cause severe colonic disease and renal failure. Their pathogenicity derives from virulence factors that enable the bacteria to colonize the colon and deliver extremely powerful toxins known as verotoxins (VT) or Shiga toxins (Stx) to the systemic circulation. The recent devastating E. coli O104:H4 epidemic in Europe has shown how helpless medical professionals are in terms of offering effective therapies. By examining the sources and distribution of these bacteria, and how they cause disease, we will be in a better position to prevent and treat the inevitable future cases of sporadic disease and victims of common source outbreaks. Due to the complexity of pathogenesis, it is likely a multitargeted approach is warranted. Developments in terms of these treatments are discussed.