Factors in the emergence of serious human infections associated with highly pathogenic strains of shiga toxin-producing Escherichia coli

A challenging STEC strain isolation from patients' stools: an O166:H15 STEC strain with the stx2 gene

Two patients with acute gastroenteritis tested positive for Shiga toxin-producing Escherichia coli (STEC) by polymerase chain reaction (PCR), and both strains carried the Shiga toxin 2 encoding gene. Since routine culture using CHROMagar STEC failed to recover these isolates, immunomagnetic separation (IMS) targeting the top six non-O157:H7 serotypes was used for isolate recovery. After two subsequent IMS runs, the STEC strains were isolated from trypticase soy broth with and without overnight enrichment for runs 1 and 2, respectively. Serotyping based on whole-genome sequencing revealed that both patients carried the strain O166:H15 STEC with the stx2 gene. Hence, the magnetic beads used in IMS appeared to have cross-reactivity with other E. coli serotypes. When the STEC isolates from both stools were cultured on CHROMagar STEC and sheep blood agar (BAP), two distinct colony sizes were apparent after overnight incubation. The small and large colonies were picked and separately cultured on both media, and colony growth was observed for 2 weeks at room temperature after an initial overnight incubation at 37°C. After 1 week, the colonies showed concentric ring structures with a darker center and a lighter surrounding on CHROMagar STEC and a "fried egg"-resembling structure with a raised circular center and a flat surrounding on BAP. Both colony types remained morphologically different on CHROMagar STEC throughout the 15 days. However, on BAP, their appearance was comparable by day 7.

IMPORTANCE

Shiga toxin-producing E. coli (STEC) infections can lead to severe complications such as bloody diarrhea and hemolytic uremic syndrome (HUS), especially in young children and the elderly. Strains that carry the shiga toxin 2 gene (stx2), such as O157:H7, have been mostly linked with severe disease outcomes. In recent years, outbreaks caused by non-O157:H7 strains have increased. E. coli O166:H15 has been previously reported causing a gastroenteritis outbreak in 1996 as a non-STEC strain, however the O166:H15 serotype we recovered carried the stx2 gene. It was particularly challenging to isolate this strain from stools by culture. Consequently, we tested immunomagnetic separation for the STEC recovery, which was a novel approach on clinical stools. Virulence genes were included for the characterization of these isolates.

Structure-Function Analysis of the A1 Subunit of Shiga Toxin 2 with Peptides That Target the P-Stalk Binding Site and Inhibit Activity

Shiga toxin 2a (Stx2a) is the virulence factor of Escherichia coli (STEC), which is associated with hemolytic uremic syndrome, the leading cause of pediatric kidney failure. The A1 subunit of Stx2a (Stx2A1) binds to the conserved C-terminal domain (CTD) of the ribosomal P-stalk proteins to remove an adenine from the sarcin-ricin loop (SRL) in the 28S rRNA, inhibiting protein synthesis. There are no antidotes against Stx2a or any other ribosome-inactivating protein (RIP). The structural and functional details of the binding of Stx2A1 to the P-stalk CTD are not known. Here, we carry out a deletion analysis of the conserved P-stalk CTD and show that the last eight amino acids (P8) of the P-stalk proteins are the minimal sequence required for optimal affinity and maximal inhibitory activity against Stx2A1. We determined the first X-ray crystal structure of Stx2A1 alone and in complex with P8 and identified the exact binding site. The C-terminal aspartic acid of the P-stalk CTD serves as an anchor, forming key contacts with the conserved arginine residues at the P-stalk binding pocket of Stx2A1. Although the ricin A subunit (RTA) binds to the P-stalk CTD, the last aspartic acid is more critical for the interaction with Stx2A1, indicating that RIPs differ in their requirements for the P-stalk. These results demonstrate that the catalytic activity of Stx2A1 is inhibited by blocking its interactions with the P-stalk, providing evidence that P-stalk binding is an essential first step in the recruitment of Stx2A1 to the SRL for depurination.

Structure-based design and optimization of a new class of small molecule inhibitors targeting the P-stalk binding pocket of ricin

Ricin, a category-B agent for bioterrorism, and Shiga toxins (Stxs), which cause food poisoning bind to the ribosomal P-stalk to depurinate the sarcin/ricin loop. No effective therapy exists for ricin or Stx intoxication. Ribosome binding sites of the toxins have not been targeted by small molecules. We previously identified CC10501, which inhibits toxin activity by binding the P-stalk pocket of ricin toxin A subunit (RTA) remote from the catalytic site. Here, we developed a fluorescence polarization assay and identified a new class of compounds, which bind P-stalk pocket of RTA with higher affinity and inhibit catalytic activity with submicromolar potency. A lead compound, RU-NT-206, bound P-stalk pocket of RTA with similar affinity as a five-fold larger P-stalk peptide and protected cells against ricin and Stx2 holotoxins for the first time. These results validate the P-stalk binding site of RTA as a critical target for allosteric inhibition of the active site.

Detection of plasma anti-lipopolysaccharide (LPS) antibodies against enterohemorrhagic Escherichia coli (EHEC) in asymptomatic kindergarten teachers from Buenos Aires province

In Argentina, hemolytic uremic syndrome (HUS) caused by EHEC has the highest incidence in the world. EHEC infection has an endemo-epidemic behavior, causing 20-30% of acute bloody diarrhea syndrome in children under 5 years old. In the period 2016-2020, 272 new cases per year were notified to the National Health Surveillance System. Multiple factors are responsible for HUS incidence in Argentina including person-to-person transmission. In order to detect possible EHEC carriers, we carried out a preliminary study of the frequency of kindergarten teachers with anti-LPS antibodies against the most prevalent EHEC serotypes in Argentina. We analyzed 61 kindergarten teachers from 26 institutions from José C. Paz district, located in the suburban area of Buenos Aires province, Argentina. Fifty-one percent of the plasma samples had antibodies against O157, O145, O121 and O103 LPS: 6.4% of the positive samples had IgM isotype (n=2), 61.3% IgG isotype (n=19) and 32.3% IgM and IgG (n=10). Given that antibodies against LPS antigens are usually short-lived specific IgM detection may indicate a recent infection. In addition, the high percentage of positive samples may indicate a frequent exposure to EHEC strains in the cohort studied, as well as the existence of a large non-symptomatic population of adults carrying pathogenic strains that could contribute to the endemic behavior through person-to-person transmission. The improvement of continuous educational programs in kindergarten institutions could be a mandatory measure to reduce HUS cases not only in Argentina but also globally.

Transduction of stx2a mediated by phage (Φ11-3088) from Escherichia coli O104:H4 in vitro and in situ during sprouting of mung beans

Escherichia coli O104:H4 strain 11-3088 encoding Stx2a is epidemiologically related to the foodborne outbreak associated with sprouts in Germany, 2011. Sprouting provides suitable conditions for bacterial growth and may lead to transduction of non-pathogenic strains of E. coli with Stx phages. Although transduction of E. coli by Stx phages in food has been documented, data on the phages from E. coli O104:H4 is limited. This study determined the host range of the bacteriophage Φ11-3088 from E. coli O104:H4 using E. coli O104:H4 ∆stx2::gfp::amp^r and demonstrated phage transduction during sprouting. The Φ11-3088∆stx transduced 5/45 strains, including generic E. coli, pap-positive E. coli O103:H2, ETEC, and S. sonnei. The expression level of Φ11-3088∆stx differed among lysogens upon induction. Of the 3 highly induced lysogens, the lytic cycle was induced in E. coli O104:H4∆stx2::gfp::amp^r and O103:H2 but not in S. sonnei. E. coli DH5α was the only strain susceptible to lytic infection by Φ11-3088∆stx. To explore the effect of drying and rehydration during seed storage and sprouting on phage induction and transduction, mung beans inoculated with the phage donor E. coli O104:H4∆stx2::gfp::amp^r (8 log CFU/g) were dried, rehydrated, and incubated with the phage recipient E. coli DH5α (7 log CFU/g) for 96 h. Sprouted seeds harbored about 3 log CFU/g of putative lysogens that acquired ampicillin resistance. At the end of sprouting, 71 % of putative lysogens encoded gfp, confirming phage transduction. Overall, stx transfer by phages may increase the cell counts of STEC during sprouting by converting generic E. coli to STEC.

The Ability of Shiga Toxin-Producing Escherichia coli to Grow in Raw Cow's Milk Stored at Low Temperatures

Despite the lack of scientific evidence, some consumers assert that raw milk is a natural food with nutritional and immunological properties superior to pasteurized milk. This has led to the increased popularity of unpasteurized cow milk (UPM) and disregard for the risks of being exposed to zoonotic infections. Dairy cattle are healthy carriers of Shiga toxin (Stx)-producing E. coli (STEC), and contaminated UPM has caused STEC outbreaks worldwide. The association between STEC, carrying the eae (E. coli attachment effacement) gene, and severe diseases is well-established. We have previously isolated four eae positive STEC isolates from two neighboring dairy farms in the Southeast of Norway. A whole genome analysis revealed that isolates from different farms exhibited nearly identical genetic profiles. To explore the risks associated with drinking UPM, we examined the ability of the isolates to produce Stx and their growth in UPM at different temperatures. All the isolates produced Stx and one of the isolates was able to propagate in UPM at 8 °C (p < 0.02). Altogether, these results highlight the risk for STEC infections associated with the consumption of UPM.

Enterohemorrhagic Escherichia coli and a Fresh View on Shiga Toxin-Binding Glycosphingolipids of Primary Human Kidney and Colon Epithelial Cells and Their Toxin Susceptibility

Enterohemorrhagic Escherichia coli (EHEC) are the human pathogenic subset of Shiga toxin (Stx)-producing E. coli (STEC). EHEC are responsible for severe colon infections associated with life-threatening extraintestinal complications such as the hemolytic-uremic syndrome (HUS) and neurological disturbances. Endothelial cells in various human organs are renowned targets of Stx, whereas the role of epithelial cells of colon and kidneys in the infection process has been and is still a matter of debate. This review shortly addresses the clinical impact of EHEC infections, novel aspects of vesicular package of Stx in the intestine and the blood stream as well as Stx-mediated extraintestinal complications and therapeutic options. Here follows a compilation of the Stx-binding glycosphingolipids (GSLs), globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) and their various lipoforms present in primary human kidney and colon epithelial cells and their distribution in lipid raft-analog membrane preparations. The last issues are the high and extremely low susceptibility of primary renal and colonic epithelial cells, respectively, suggesting a large resilience of the intestinal epithelium against the human-pathogenic Stx1a- and Stx2a-subtypes due to the low content of the high-affinity Stx-receptor Gb3Cer in colon epithelial cells. The review closes with a brief outlook on future challenges of Stx research.

Synergistic Effects of Bacteriophage vB_Eco4-M7 and Selected Antibiotics on the Biofilm Formed by Shiga Toxin-Producing Escherichia coli

Apart from antibiotic resistance of pathogenic bacteria, the formation of biofilms is a feature that makes bacterial infections especially difficulty to treat. Shiga toxin-producing Escherichia coli (STEC) strains are dangerous pathogens, causing severe infections in humans, and capable of biofilm production. We have reported previously the identification and characterization of the vB_Eco4-M7 bacteriophage, infecting various STEC strains. It was suggested that this phage might be potentially used in phage therapy against these bacteria. Here, we tested the effects of vB_Eco4-M7 alone or in a phage cocktail with another STEC-infecting phage, and/or in a combination with different antibiotics (ciprofloxacin and rifampicin) on biofilm formed by a model STEC strain, named E. coli O157:H7 (ST2-8624). The vB_Eco4-M7 phage appeared effective in anti-biofilm action in all these experimental conditions (2–3-fold reduction of the biofilm density, and 2–3 orders of magnitude reduction of the number of bacterial cells). However, the highest efficiency in reducing a biofilm’s density and number of bacterial cells was observed when phage infection preceded antibiotic treatment (6-fold reduction of the biofilm density, and 5–6 orders of magnitude reduction of the number of bacterial cells). Previous reports indicated that the use of antibiotics to treat STEC-caused infections might be dangerous due to the induction of Shiga toxin-converting prophages from bacterial genomes under stress conditions caused by antibacterial agents. We found that ciprofloxacin was almost as efficient in inducing prophages from the E. coli O15:H7 (ST2-8624) genome as a classical inducer, mitomycin C, while no detectable prophage induction could be observed in rifampicin-treated STEC cells. Therefore, we conclude the latter antibiotic or similarly acting compounds might be candidate(s) as effective and safe drug(s) when used in combination with phage therapy to combat STEC-mediated infections.

Epidemiology of Non-O157 Shiga Toxin-Producing Escherichia coli in the Province of Alberta, Canada, from 2018 to 2021

Non-O157 serogroups contribute significantly to the burden of disease caused by Shiga toxin-producing Escherichia coli (STEC) and have been underrecognized by traditional detection algorithms. We described the epidemiology of non-O157 STEC in Alberta, Canada for the period of 2018 to 2021. All non-O157 STEC isolated from clinical samples were submitted for serotyping and qPCR targeting the stx₁ and stx₂ genes. A total of 729 isolates were identified. Increased detection occurred over the summer months, peaking in July. Patients 18 years and younger made up 42.4% of cases, with 31.1% in those 0–9 years of age. There was a slight female predominance (399/729, 54.7%) A total of 50 different serogroups were detected; the most common were O26 (30.3%), O103 (15.9%), O111 (12.8%), O121 (11.0%), O118 (3.3%) and O71 (2.9%). These six serogroups made up 76.2% of all isolates. In total, 567 (77.8%) were positive for stx₁, 114 (15.6%) were positive for stx₂ and 48 (6.6%) were positive for both stx₁ and stx₂. A wide variety of non-O157 serogroups have been detected in Alberta, with the most frequent serogroups differing from other locations. These results highlight the need for further characterization of their virulence factors and clinical impact.

Genotyping Based on CRISPR Loci Diversity and Pathogenic Potential of Diarrheagenic Escherichia coli

Diarrheagenic Escherichia coli (DEC) can cause epidemic diarrhea worldwide. The pathogenic potential of different strains is diverse and the continuous emergence of pathogenic strains has brought serious harm to public health. Accurately distinguishing and identifying DEC with different virulence is necessary for epidemiological surveillance and investigation. Clustered regularly interspaced short palindromic repeats (CRISPR) typing is a new molecular method that can distinguish pathogenic bacteria excellently and has shown great promise in DEC typing. The purpose of this study was to investigate the discrimination of CRISPR typing method for DEC and explore the pathogenicity potential of DEC based on CRISPR types (CT). The whole genome sequences of 789 DEC strains downloaded from the database were applied CRISPR typing and serotyping. The D value (Simpson’s index) with 0.9709 determined that CRISPR typing had a higher discrimination. Moreover, the same H antigen strains with different O seemed to share more identical spacers. Further analyzing the strains CRISPR types and the number of virulence genes, it was found that there was a significant correlation between the CRISPR types and the number of virulence genes (p < 0.01). The strains with the largest number of virulence genes concentrated in CT25 and CT56 and the number of virulence genes in CT264 was the least, indicating that the pathway potential of different CRISPR types was variable. Combined with the Caco-2 cell assay of the laboratory strains, the invasion capacity of STEC strains of different CRISPR types was different and there was no significant difference in the invasion rate between different CRISPR type strains (p > 0.05). In the future, with the increase of the number of strains that can be studied experimentally, the relationship between CRISPR types and adhesion and invasion capacities will be further clarified.

A trait-based framework for predicting foodborne pathogen risk from wild birds

Recent foodborne illness outbreaks have heightened pressures on growers to deter wildlife from farms, jeopardizing conservation efforts. However, it remains unclear which species, particularly birds, pose the greatest risk to food safety. Using >11,000 pathogen tests and 1565 bird surveys covering 139 bird species from across the western United States, we examined the importance of 11 traits in mediating wild bird risk to food safety. We tested whether traits associated with pathogen exposure (e.g., habitat associations, movement, and foraging strategy) and pace-of-life (clutch size and generation length) mediated foodborne pathogen prevalence and proclivities to enter farm fields and defecate on crops. Campylobacter spp. were the most prevalent enteric pathogen (8.0%), while Salmonella and Shiga-toxin producing Escherichia coli (STEC) were rare (0.46% and 0.22% prevalence, respectively). We found that several traits related to pathogen exposure predicted pathogen prevalence. Specifically, Campylobacter and STEC-associated virulence genes were more often detected in species associated with cattle feedlots and bird feeders, respectively. Campylobacter was also more prevalent in species that consumed plants and had longer generation lengths. We found that species associated with feedlots were more likely to enter fields and defecate on crops. Our results indicated that canopy-foraging insectivores were less likely to deposit foodborne pathogens on crops, suggesting growers may be able to promote pest-eating birds and birds of conservation concern (e.g., via nest boxes) without necessarily compromising food safety. As such, promoting insectivorous birds may represent a win-win-win for bird conservation, crop production, and food safety. Collectively, our results suggest that separating crop production from livestock farming may be the best way to lower food safety risks from birds. More broadly, our trait-based framework suggests a path forward for co-managing wildlife conservation and food safety risks in farmlands by providing a strategy for holistically evaluating the food safety risks of wild animals, including under-studied species.

Association of Common Zoonotic Pathogens With Concentrated Animal Feeding Operations

Animal farming has intensified significantly in recent decades, with the emergence of concentrated animal feeding operations (CAFOs) in industrialized nations. The congregation of susceptible animals in CAFOs can lead to heavy environmental contamination with pathogens, promoting the emergence of hyper-transmissible, and virulent pathogens. As a result, CAFOs have been associated with emergence of highly pathogenic avian influenza viruses, hepatitis E virus, Escherichia coli O157:H7, Streptococcus suis, livestock-associated methicillin-resistant Staphylococcus aureus, and Cryptosporidium parvum in farm animals. This has led to increased transmission of zoonotic pathogens in humans and changes in disease patterns in general communities. They are exemplified by the common occurrence of outbreaks of illnesses through direct and indirect contact with farm animals, and wide occurrence of similar serotypes or subtypes in both humans and farm animals in industrialized nations. Therefore, control measures should be developed to slow down the dispersal of zoonotic pathogens associated with CAFOs and prevent the emergence of new pathogens of epidemic and pandemic potential.

Antimicrobial potential and in vitro cytotoxicity study of polyvinyl pyrollidone-stabilised silver nanoparticles synthesised from Lysinibacillus boronitolerans

The main emphasis herein is on the eco‐friendly synthesis and assessment of the antimicrobial potential of silver nanoparticles (AgNPs) and a cytotoxicity study. Silver nanoparticles were synthesised by an extracellular method using bacterial supernatant. Biosynthesised silver nanoparticles were characterised by UV‐vis spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, dynamic light scattering, and zeta potential analysis. The synthesised silver nanoparticles exhibited a characteristic peak at 420 nm. TEM analysis depicted the spherical shape and approximately 20 nm size of nanoparticles. Silver nanoparticles carry a charge of −33.75 mV, which confirms their stability. Biogenic polyvinyl pyrrolidone‐coated AgNPs exhibited significant antimicrobial effects against all opportunistic pathogens (Gram‐positive and Gram‐negative bacteria, and fungi). Silver nanoparticles equally affect the growth of both Gram‐positive and Gram‐negative bacteria, with a maximum inhibition zone observed at 22 mm and a minimum at 13 mm against Pseudomonas aeruginosa and Fusarium graminearum, respectively. The minimum inhibitory concentration (MIC) of AgNPs against P. aeruginosa and Staphylococcus aureus was recorded at between 15 and 20 μg/ml. Synthesised nanoparticles exhibited a significant synergistic effect in combination with conventional antibiotics. Cytotoxicity estimates using C2C12 skeletal muscle cell line via 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) test and lactate dehydrogenase assay were directly related to the concentration of AgNPs and length of exposure. On the basis of the MTT test, the IC50 of AgNPs for the C2C12 cell line was approximately 5.45 μg/ml concentration after 4 h exposure.

Transcriptional analysis reveals specific niche factors and response to environmental stresses of enterohemorrhagic Escherichia coli O157:H7 in bovine digestive contents

Background

Enterohemorrhagic Escherichia coli (EHEC) are responsible for severe diseases in humans, and the ruminant digestive tract is considered as their main reservoir. Their excretion in bovine feces leads to the contamination of foods and the environment. Thus, providing knowledge of processes used by EHEC to survive and/or develop all along the bovine gut represents a major step for strategies implementation.

Results

We compared the transcriptome of the reference EHEC strain EDL933 incubated in vitro in triplicate samples in sterile bovine rumen, small intestine and rectum contents with that of the strain grown in an artificial medium using RNA-sequencing (RNA-seq), focusing on genes involved in stress response, adhesion systems including the LEE, iron uptake, motility and chemotaxis. We also compared expression of these genes in one digestive content relative to the others. In addition, we quantified short chain fatty acids and metal ions present in the three digestive contents. RNA-seq data first highlighted response of EHEC EDL933 to unfavorable physiochemical conditions encountered during its transit through the bovine gut lumen. Seventy-eight genes involved in stress responses including drug export, oxidative stress and acid resistance/pH adaptation were over-expressed in all the digestive contents compared with artificial medium. However, differences in stress fitness gene expression were observed depending on the digestive segment, suggesting that these differences were due to distinct physiochemical conditions in the bovine digestive contents. EHEC activated genes encoding three toxin/antitoxin systems in rumen content and many gene clusters involved in motility and chemotaxis in rectum contents. Genes involved in iron uptake and utilization were mostly down-regulated in all digestive contents compared with artificial medium, but feo genes were over-expressed in rumen and small intestine compared with rectum. The five LEE operons were more expressed in rectum than in rumen content, and LEE1 was also more expressed in rectum than in small intestine content.

Conclusion

Our results highlight various strategies that EHEC may implement to survive in the gastrointestinal environment of cattle. These data could also help defining new targets to limit EHEC O157:H7 carriage and shedding by cattle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02343-7.

A Validation System for Selection of Bacteriophages against Shiga Toxin-Producing Escherichia coli Contamination

Shiga toxin-producing Escherichia coli (STEC) can cause severe infections in humans, leading to serious diseases and dangerous complications, such as hemolytic-uremic syndrome. Although cattle are a major reservoir of STEC, the most commonly occurring source of human infections are food products (e.g., vegetables) contaminated with cow feces (often due to the use of natural fertilizers in agriculture). Since the use of antibiotics against STEC is controversial, other methods for protection of food against contaminations by these bacteria are required. Here, we propose a validation system for selection of bacteriophages against STEC contamination. As a model system, we have employed a STEC-specific bacteriophage vB_Eco4M-7 and the E. coli O157:H7 strain no. 86-24, bearing Shiga toxin-converting prophage ST2-8624 (Δstx2::cat gfp). When these bacteria were administered on the surface of sliced cucumber (as a model vegetable), significant decrease in number viable E. coli cells was observed after 6 h of incubation. No toxicity of vB_Eco4M-7 against mammalian cells (using the Balb/3T3 cell line as a model) was detected. A rapid decrease of optical density of STEC culture was demonstrated following addition of a vB_Eco4M-7 lysate. However, longer incubation of susceptible bacteria with this bacteriophage resulted in the appearance of phage-resistant cells which predominated in the culture after 24 h incubation. Interestingly, efficiency of selection of bacteria resistant to vB_Eco4M-7 was higher at higher multiplicity of infection (MOI); the highest efficiency was evident at MOI 10, while the lowest occurred at MOI 0.001. A similar phenomenon of selection of the phage-resistant bacteria was also observed in the experiment with the STEC-contaminated cucumber after 24 h incubation with phage lysate. On the other hand, bacteriophage vB_Eco4M-7 could efficiently develop in host bacterial cells, giving plaques at similar efficiency of plating at 37, 25 and 12 °C, indicating that it can destroy STEC cells at the range of temperatures commonly used for vegetable short-term storage. These results indicate that bacteriophage vB_Eco4M-7 may be considered for its use in food protection against STEC contamination; however, caution should be taken due to the phenomenon of the appearance of phage-resistant bacteria.

Insights into the genome architecture and evolution of Shiga toxin encoding bacteriophages of Escherichia coli

Background

A total of 179 Shiga toxin-producing Escherichia coli (STEC) complete genomes were analyzed in terms of serotypes, prophage coding regions, and stx gene variants and their distribution. We further examined the genetic diversity of Stx-converting phage genomes (Stx phages), focusing on the lysis-lysogeny decision and lytic cassettes.

Results

We show that most STEC isolates belong to non-O157 serotypes (73 %), regardless the sources and geographical regions. While the majority of STEC genomes contain a single stx gene (61 %), strains containing two (35 %), three (3 %) and four (1 %) stx genes were also found, being stx2 the most prevalent gene variant. Their location is exclusively found in intact prophage regions, indicating that they are phage-borne. We further demonstrate that Stx phages can be grouped into four clusters (A, B, C and D), three subclusters (A1, A2 and A3) and one singleton, based on their shared gene content. This cluster distribution is in good agreement with their predicted virion morphologies. Stx phage genomes are highly diverse with a vast number of 1,838 gene phamilies (phams) of related sequences (of which 677 are orphams i.e. unique genes) and, although having high mosaicism, they are generally organized into three major transcripts. While the mechanisms that guide lysis–lysogeny decision are complex, there is a strong selective pressure to maintain the stx genes location close to the lytic cassette composed of predicted SAR-endolysin and pin-holin lytic proteins. The evolution of STEC Stx phages seems to be strongly related to acquiring genetic material, probably from horizontal gene transfer events.

Conclusions

This work provides novel insights on the genetic structure of Stx phages, showing a high genetic diversity throughout the genomes, where the various lysis-lysogeny regulatory systems are in contrast with an uncommon, but conserved, lytic system always adjacent to stx genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07685-0.

EHEC O111:H8 strain and norovirus GII.4 Sydney [P16] causing an outbreak in a daycare center, Brazil, 2019

Background

This study describes the investigation of an outbreak of diarrhea, hemorrhagic colitis (HC), and hemolytic uremic syndrome (HUS) at a daycare center in southeastern Brazil, involving fourteen children, six staff members, six family members, and one nurse. All bacterial and viral pathogens detected were genetically characterized.

Results

Two isolates of a strain of enterohemorrhagic Escherichia coli (EHEC) serotype O111:H8 were recovered, one implicated in a case of HUS and the other in a case of uncomplicated diarrhea. These isolates had a clonal relationship of 94% and carried the stx2a and eae virulence genes and the OI-122 pathogenicity island. The EHEC strain was determined to be a single-locus variant of sequence type (ST) 327. EHEC isolates were resistant to ofloxacin, doxycycline, tetracycline, ampicillin, and trimethoprim-sulfamethoxazole and intermediately resistant to levofloxacin and ciprofloxacin. Rotavirus was not detected in any samples, and norovirus was detected in 46.7% (14/30) of the stool samples, three of which were from asymptomatic staff members. The noroviruses were classified as the recombinant GII.4 Sydney [P16] by gene sequencing.

Conclusion

In this outbreak, it was possible to identify an uncommon stx2a + EHEC O111:H8 strain, and the most recent pandemic norovirus strain GII.4 Sydney [P16]. Our findings reinforce the need for surveillance and diagnosis of multiple enteric pathogens by public health authorities, especially during outbreaks.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02161-x.

Animal petting zoos as sources of Shiga toxin-producing Escherichia coli, Salmonella and extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae

Animal petting zoos and farm fairs provide the opportunity for children and adults to interact with animals, but contact with animals carries a risk of exposure to zoonotic pathogens and antimicrobial-resistant bacteria. The aim of this study was to assess the occurrence of Shiga toxin-producing Escherichia coli (STEC), Salmonella, extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae and methicillin-resistant Staphylococcus aureus (MRSA) in animal faeces from six animal petting zoos and one farm fair in Switzerland. Furthermore, hygiene facilities on the venues were evaluated. Of 163 faecal samples, 75 contained stx1, stx2 or stx1/stx2 genes, indicating the presence of STEC. Samples included faeces from sika deer (100%), sheep (92%), goats (88%), mouflons (80%), camels (62%), llamas (50%), yaks (50%), pigs (29%) and donkeys (6%), whereas no stx genes were isolated from faeces of calves, guinea pigs, hens, ostriches, ponies, zebras or zebus. Salmonella enterica subsp. enterica serovar Stourbridge (S. Stourbridge) was detected in faecal samples from camels. A total of four ESBL-producing E. coli strains were isolated from faeces of goats, camels and pigs. PCR and sequencing identified the presence of bla_CTX-M-15 in three and bla_CTX-M-65 in one E. coli. Antimicrobial resistance profiling using the disk diffusion method revealed two multidrug-resistant (MDR) E. coli with resistance to ciprofloxacin, gentamicin and azithromycin, all of which are critically important drugs for human medicine. Multilocus sequence typing identified E. coli ST162, E. coli ST2179, extraintestinal high-risk E. coli ST410 and E. coli ST4553, which belongs to the emerging extraintestinal clonal complex (CC) 648. No MRSA was detected. On all animal petting venues, there were inadequacies with regard to access to hygiene information and handwashing hygiene facilities. This study provides data that underscore the importance of hygiene measures to minimize the risk of transmission of zoonotic pathogens and MDR, ESBL-producing E. coli to visitors of animal petting venues.

The extracellular juncture domains in the intimin passenger adopt a constitutively extended conformation inducing restraints to its sphere of action

Enterohemorrhagic and enteropathogenic Escherichia coli are among the most important food-borne pathogens, posing a global health threat. The virulence factor intimin is essential for the attachment of pathogenic E. coli to the intestinal host cell. Intimin consists of four extracellular bacterial immunoglobulin-like (Big) domains, D00–D2, extending into the fifth lectin subdomain (D3) that binds to the Tir-receptor on the host cell. Here, we present the crystal structures of the elusive D00–D0 domains at 1.5 Å and D0–D1 at 1.8 Å resolution, which confirms that the passenger of intimin has five distinct domains. We describe that D00–D0 exhibits a higher degree of rigidity and D00 likely functions as a juncture domain at the outer membrane-extracellular medium interface. We conclude that D00 is a unique Big domain with a specific topology likely found in a broad range of other inverse autotransporters. The accumulated data allows us to model the complete passenger of intimin and propose functionality to the Big domains, D00–D0–D1, extending directly from the membrane.

Molecular characteristics of eae-positive clinical Shiga toxin-producing Escherichia coli in Sweden

Shiga toxin (Stx)-producing Escherichia coli (STEC) can cause a wide range of symptoms from asymptomatic carriage, mild diarrhea to bloody diarrhea (BD) and hemolytic uremic syndrome (HUS). Intimin, encoded by the eae gene, also plays a critical role in STEC pathogenesis. Herein, we investigated the prevalence and genetic diversity of eae among clinical STEC isolates from patients with diarrhea, BD, HUS as well as from asymptomatic STEC-positive individuals in Sweden with whole-genome sequencing. We found that 173 out of 239 (72.4%) of clinical STEC strains were eae positive. Six eae subtypes (ϵ1, γ1, β3, θ, ζ and ρ) were identified eae and its subtype γ1 were significantly overrepresented in O157:H7 strains isolated from BD and HUS patients. ϵ1 was associated with O121:H19 and O103:H2 strains, and β3 to O26:H11 strains. The combination of eae subtype γ1 and stx subtype (stx 2 or stx 1+stx 2) is more likely to cause severe disease, suggesting the possibility of using eae genotypes in risk assessment of STEC infection. In summary, this study demonstrated a high prevalence of eae in clinical STEC strains and considerable genetic diversity of eae in STEC strains in Sweden from 1994 through 2018, and revealed association between eae subtypes and disease severity.

Effects of antimicrobials on Shiga toxin production in high-virulent Shiga toxin-producing Escherichia coli

PURPOSE

Antimicrobial treatment of Shiga toxin-producing Escherichia coli (STEC) infections is controversial because antimicrobials may stimulate Shiga toxin (Stx) production, and thereby increase the risk of developing haemolytic uremic syndrome (HUS). Previous in vitro studies have shown this mainly in infections caused by STEC serotype O157:H7. The aim of this study was to investigate induction of Stx transcription and production in different serotypes of STEC isolated from severely ill patients, following their exposure in vitro to six different classes of antimicrobials.

METHODS

We investigated Stx transcription and production in 12 high-virulent STEC strains, all carrying the stx2a gene, of six different serotypes following their exposure to six classes of antimicrobials. Liquid cultures of the STEC strains were incubated with sub-inhibitory concentrations of the antimicrobials. We used reverse-transcription quantitative PCR to measure the relative expression of Stx2a mRNA and an enzyme-linked immunosorbent assay to quantify Stx production.

RESULTS

In general the antibiotics tested showed only minor effects on transcriptional levels of Stx2a. Ciprofloxacin caused an increase of Stx production in all but two strains, while gentamicin, meropenem and azithromycin did not induce Stx production in any of the STEC strains examined. STEC O104:H4 was the serotype that in greatest extent responded to antimicrobial exposure with an increase of stx2a transcription and Stx production.

CONCLUSION

Gentamicin, meropenem and azithromycin exposure did not result in elevated Stx production. We recommend that this finding is investigated further in the search for candidates for future antimicrobial treatment of STEC.

Shiga Toxin-Producing Escherichia coli Infections Associated With Romaine Lettuce-United States, 2018

BACKGROUND

Produce-associated outbreaks of Shiga toxin-producing Escherichia coli (STEC) were first identified in 1991. In April 2018, New Jersey and Pennsylvania officials reported a cluster of STEC O157 infections associated with multiple locations of a restaurant chain. The Centers for Disease Control and Prevention (CDC) queried PulseNet, the national laboratory network for foodborne disease surveillance, for additional cases and began a national investigation.

METHODS

A case was defined as an infection between 13 March and 22 August 2018 with 1 of the 22 identified outbreak-associated E. coli O157:H7 or E. coli O61 pulsed-field gel electrophoresis pattern combinations, or with a strain STEC O157 that was closely related to the main outbreak strain by whole-genome sequencing. We conducted epidemiologic and traceback investigations to identify illness subclusters and common sources. A US Food and Drug Administration-led environmental assessment, which tested water, soil, manure, compost, and scat samples, was conducted to evaluate potential sources of STEC contamination.

RESULTS

We identified 240 case-patients from 37 states; 104 were hospitalized, 28 developed hemolytic uremic syndrome, and 5 died. Of 179 people who were interviewed, 152 (85%) reported consuming romaine lettuce in the week before illness onset. Twenty subclusters were identified. Product traceback from subcluster restaurants identified numerous romaine lettuce distributors and growers; all lettuce originated from the Yuma growing region. Water samples collected from an irrigation canal in the region yielded the outbreak strain of STEC O157.

CONCLUSIONS

We report on the largest multistate leafy greens-linked STEC O157 outbreak in several decades. The investigation highlights the complexities associated with investigating outbreaks involving widespread environmental contamination.

Nitroso-hemoglobin-ginger conjugates effects on bacterial growth and color stability in a minced beef model

This study aims to enhance the color and microbiological qualities of a raw beef using natural ingredients. Nitroso-hemoglobin (NO-Hb) integrated with vitamin C (VC), calcium lactate, and ginger complexation were used as natural inhibitors against the growth of aerobic and pathogenic bacteria, namely (Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Salmonella. NO-Hb inhibited E. coli, S. aureus, and Salmonella, and enhanced the color stability more than nitrite in the minced beef model. After the multiexponential analysis of relaxation decays, the water component (T2b) was analyzed using the low-field NMR. The results indicated that, at the 7th d of cold-storage the third component (T2) was detected. Significant correlations were observed between T21 and T22 relaxation times and water-holding capacity in minced beef, implying that the LF-NMR measurements could be an efficient method for the determination and prediction of beef freshness. NO-Hb- ginger mixture, as a novel ingredient, could be used instead of nitrite in terms of meat safety.

Population genetic analysis suggests genetic recombination is responsible for increased zoonotic potential of Enterocytozoon bieneusi from ruminants in China

Enterocytozoon bieneusi is a zoonotic pathogen with worldwide distribution. Among the 11 established groups of E. bieneusi genotypes based on phylogenetic analysis of the ribosomal internal transcribed spacer (ITS), the human-infective potential and population genetics of the Group 1 genotypes from diverse hosts are well characterized. In contrast, Group 2 genotypes from ruminants have unclear population genetics, leading to poor understanding of their host range and zoonotic potential. In this study, we sequence-characterized 121 Group 2 isolates from dairy cattle, beef cattle, yaks, Tibetan sheep, golden takins, and deer from China at five genetic loci (ITS, MS1, MS3, MS4 and MS7), comparing with data from 113 Group 1 isolates from nonhuman primates. Except for MS7, most of the genetic loci produced efficient PCR amplification and high nucleotide identity between Groups 1 and 2 of E. bieneusi genotypes. In population genetic analyses of the sequence data, a strong linkage disequilibrium was observed among these genetic loci in the overall Group 2 population. The individual ITS genotypes (I, J and BEB4) within Group 2, however, had reduced linkage disequilibrium and increased genetic exchanges among isolates. There was only partial genetic differentiation between Group 1 and Group 2 genotypes, with some occurrence of genetic recombination between them. Genetic recombination was especially common between genotypes I and J within Group 2. The data presented indicate a high genetic identity between Group 1 and Group 2 genotypes of E. bieneusi, which could be responsible for the broad host range and high zoonotic potential of Group 2 genotypes in China. As there is no effective treatment against E. bieneusi, the One Health approach should be used in the control and prevention of zoonotic transmission of the pathogen.

Formation of Complexes Between O Proteins and Replication Origin Regions of Shiga Toxin-Converting Bacteriophages

Shiga toxin-converting bacteriophages (or Stx phages) are responsible for virulence of enterohemorrhagic Escherichia coli strains. Although they belong to the group of lambdoid phages, which have served as models in studies on DNA replication mechanisms, details of regulation of replication of Stx phage genomes are poorly understood. Despite high similarity of their replication regions to that of phage lambda, considerable differences occur between them. Here, we present a comparison of origins of replication and O proteins of lambda and selected Stx phages (phages P27 and 933W). Stx initiator proteins, similarly to the lambda O protein, exist in the form of dimers. Only 4 iteron sequences are strongly bound in vitro by the O proteins, despite the presence of 6 such fragments in the Stx ori, while the function of the other two iterons is still crucial for transformation of E. coli wild-type strain by the P27-derived lambdoid plasmid. As these sequences are found in the gene coding for Stx O proteins, the sequences of these proteins themselves are also extended compared to lambda phage. Therefore, proteins O of Stx phages P27 and 933W have 13 additional amino acids. They can act as a space barrier, thus affecting the lesser packing of the O-some Stx complex compared to the structure found in lambda. Such structure of the DNA replication initiation complex may determine its lesser dependence on the processes occurring in the host cell, including transcriptional activation of the origin. Differences between molecular processes occurring during formation of replication complexes in lambda and Stx phages may indicate the specialization of the latter phages and their adaptation to specific environmental conditions where quick genetic switches are crucial.

Investigation on the Evolution of Shiga Toxin-Converting Phages Based on Whole Genome Sequencing

Bacteriophages are pivotal elements in the dissemination of virulence genes. The main virulence determinants of Shiga Toxin producing E. coli, Shiga Toxins (Stx), are encoded by genes localized in the genome of lambdoid bacteriophages. Stx comprise two antigenically different types, Stx1 and Stx2, further divided into subtypes. Among these, certain Stx2 subtypes appear to be more commonly occurring in the most severe forms of the STEC disease, haemorrhagic colitis and haemolytic uremic syndrome (HUS). This study aimed at obtaining insights on the evolution of Stx2 bacteriophages, due to their relevance in public health, and we report here on the analysis of the genomic structure of Stx2 converting phages in relation with the known reservoir of the E. coli strains harboring them. Stx2-converting phages conveying the genes encoding different stx2 subtypes have been isolated from STEC strains and their whole genomes have been sequenced, analyzed and compared to those of other Stx2 phages available in the public domain. The phages' regions containing the stx2 genes have been analyzed in depth allowing to make inference on the possible mechanisms of selection and maintenance of certain Stx2 phages in the reservoir. The "stx regions" of different stx2 gene subtypes grouped into three different evolutionary lines in the comparative analysis, reflecting the frequency with which these subtypes are found in different animal niches, suggesting that the colonization of specific reservoir by STEC strains could be influenced by the Stx phage that they carry. Noteworthy, we could identify the presence of nanS-p gene exclusively in the "stx regions" of the phages identified in STEC strains commonly found in cattle. As a matter of fact, this gene encodes an esterase capable of metabolizing sialic acids produced by submaxillary glands of bovines and present in great quantities in their gastrointestinal tract.

Salmonella enterica and Escherichia coli in Wheat Flour: Detection and Serotyping by a Quasimetagenomic Approach Assisted by Magnetic Capture, Multiple-Displacement Amplification, and Real-Time Sequencing

Food safety is a new area for novel applications of metagenomics analysis, which not only can detect and subtype foodborne pathogens in a single workflow but may also produce additional information with in-depth analysis capabilities. In this study, we applied a quasimetagenomic approach by combining short-term enrichment, immunomagnetic separation (IMS), multiple-displacement amplification (MDA), and nanopore sequencing real-time analysis for simultaneous detection of Salmonella and Escherichia coli in wheat flour. Tryptic soy broth was selected for the 12-h enrichment of samples at 42°C. Enrichments were subjected to IMS using beads capable of capturing both Salmonella and E. coli MDA was performed on harvested beads, and amplified DNA fragments were subjected to DNA library preparation for sequencing. Sequencing was performed on a portable device with real-time basecalling adaptability, and resulting sequences were subjected to two parallel pipelines for further analysis. After 1 h of sequencing, the quasimetagenomic approach could detect all targets inoculated at approximately 1 CFU/g flour to the species level. Discriminatory power was determined by simultaneous detection of dual inoculums of Salmonella and E. coli, absence of detection in control samples, and consistency in microbial flora composition of the same flour samples over several rounds of experiments. The total turnaround time for detection was approximately 20 h. Longer sequencing for up to 15 h enabled serotyping for many of the samples with more than 99% genome coverage, which could be subjected to other appropriate genetic analysis pipelines in less than a total of 36 h.IMPORTANCE Enterohemorrhagic Escherichia coli (EHEC) and Salmonella are of serious concern in low-moisture foods, including wheat flour and its related products, causing illnesses, outbreaks, and recalls. The development of advanced detection methods based on molecular principles of analysis is essential to incorporate into interventions intended to reduce the risk from these pathogens. In this work, a quasimetagenomic method based on real-time sequencing analysis and assisted by magnetic capture and DNA amplification was developed. This protocol is capable of detecting multiple Salmonella and/or E. coli organisms in the sample within less than a day, and it can also generate sufficient whole-genome sequences of the target organisms suitable for subsequent bioinformatics analysis. Multiplex detection and identification were accomplished in less than 20 h and additional whole-genome analyses of different nature were attained within 36 h, in contrast to the several days required in previous sequencing pipelines.

Valid Presumption of Shiga Toxin-Mediated Damage of Developing Erythrocytes in EHEC-Associated Hemolytic Uremic Syndrome

The global emergence of clinical diseases caused by enterohemorrhagic Escherichia coli (EHEC) is an issue of great concern. EHEC release Shiga toxins (Stxs) as their key virulence factors, and investigations on the cell-damaging mechanisms toward target cells are inevitable for the development of novel mitigation strategies. Stx-mediated hemolytic uremic syndrome (HUS), characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal injury, is the most severe outcome of an EHEC infection. Hemolytic anemia during HUS is defined as the loss of erythrocytes by mechanical disruption when passing through narrowed microvessels. The formation of thrombi in the microvasculature is considered an indirect effect of Stx-mediated injury mainly of the renal microvascular endothelial cells, resulting in obstructions of vessels. In this review, we summarize and discuss recent data providing evidence that HUS-associated hemolytic anemia may arise not only from intravascular rupture of erythrocytes, but also from the extravascular impairment of erythropoiesis, the development of red blood cells in the bone marrow, via direct Stx-mediated damage of maturing erythrocytes, leading to “non-hemolytic” anemia.

Therapeutic Effect of Antibiotics Against Escherichia coli O157:H7 in Silk Moth Larvae Animal Model

The increasing clinical incidence of antibiotic resistance in bacteria is a major global health care issue. Rampant use of antimicrobials is one of the major reasons of the dramatic rise in antibiotic-resistant bacterial strains. Suitable animal models are required to improve our understanding of bacterial pathogenicity, evolution and search for novel antibiotics. The larvae of the silk moth (commonly called silkworm), Bombyx mori, have been used as an animal model for testing the pathogenicity of a clinically isolated strain of enterohemorrhagic Escherichia coli O157:H7 upon injection through hemolymph. Here, we show that a foodborne E. coli O157:H7 strain can kill silkworm larvae upon injection through either hemolymph (blood) or midgut. Bacterial number in the hemolymph started to increase after 3 h of injection into hemolymph, while the number of viable circulating hemocytes decreased. Administration of four well-known antibiotics into the larval hemolymph up to 100 µg per larva showed therapeutic effect with varying efficacies against E. coli O157:H7 with ceftriaxone and imipenem showing better effect. Our findings indicate that silkworm larvae can be used as an animal model to screen for novel antibiotics that are effective against E. coli O157:H7.

Ultraviolet Irradiation Enhances the Microbicidal Activity of Silver Nanoparticles by Hydroxyl Radicals

It is known that silver has microbicidal qualities; even at a low concentration, silver is active against many kinds of bacteria. Silver nanoparticles (AgNPs) have been extensively studied for a wide range of applications. Alternately, the toxicity of silver to human cells is considerably lower than that to bacteria. Recent studies have shown that AgNPs also have antiviral activity. We found that large amounts of hydroxyl radicals—highly reactive molecular species—are generated when AgNPs are irradiated with ultraviolet (UV) radiation with a wavelength of 365 nm, classified as ultraviolet A (UVA). In this study, we used electron spin resonance direct detection to confirm that UV irradiation of AgNPs produced rapid generation of hydroxyl radicals. As hydroxyl radicals are known to degrade bacteria, viruses, and some chemicals, the enhancement of the microbicidal activity of AgNPs by UV radiation could be valuable for the protection of healthcare workers and the prevention of the spread of infectious diseases.

Phage Biocontrol Improves Food Safety by Significantly Reducing the Level and Prevalence of Escherichia coli O157:H7 in Various Foods

ABSTRACT

Management of Shiga toxin-producing Escherichia coli (STEC), including E. coli O157:H7, in food products is a major challenge for the food industry. Several interventions, such as irradiation, chemical disinfection, and pasteurization, have had variable success controlling STEC contamination. However, these interventions also indiscriminately kill beneficial bacteria in foods, may impact organoleptic properties of foods, and are not always environmentally friendly. Biocontrol using bacteriophage-based products to reduce or eliminate specific foodborne pathogens in food products has been gaining attention due to the specificity, safety, and environmentally friendly properties of lytic bacteriophages. We developed EcoShield PX, a cocktail of lytic bacteriophages, that specifically targets STEC. This study was conducted to examine the efficacy of this bacteriophage cocktail for reducing the levels of E. coli O157:H7 in eight food products: beef chuck roast, ground beef, chicken breast, cooked chicken, salmon, cheese, cantaloupe, and romaine lettuce. The food products were challenged with E. coli O157:H7 at ca. 3.0 log CFU/g and treated with the bacteriophage preparation at ca. 1 × 106, 5 × 106, or 1 × 107 PFU/g. Application of 5 × 106 and 1 × 107 PFU/g resulted in significant reductions (P < 0.05) in E. coli O157:H7 levels of up to 97% in all foods. When bacteriophages (ca. 1 × 106 PFU/g) were used to treat lower levels of E. coli O157:H7 (ca. 1 to 10 CFU/10 g) on beef chuck roast samples, mimicking the levels of STEC found under real-life conditions in food processing plants, the prevalence of STEC in the samples was significantly reduced (P < 0.05) by ≥80%. Our results suggest that this STEC-targeting bacteriophage preparation can result in significant reduction of both the levels and prevalence of STEC in various foods and, therefore, may help improve the safety and reduce the risk of recalls of foods at high risk for STEC contamination.

HIGHLIGHTS

Genetic diversity of the intimin gene (eae) in non-O157 Shiga toxin-producing Escherichia coli strains in China

Shiga toxin-producing Escherichia coli (STEC) is an important foodborne pathogen. The increasing incidence of non-O157 STEC has posed a great risk to public health. Besides the Shiga toxin (Stx), the adherence factor, intimin, coded by eae gene plays a critical role in STEC pathogenesis. In this study, we investigated the prevalence and polymorphisms of eae gene in non-O157 STEC strains isolated from different sources in China. Among 735 non-O157 STEC strains, eae was present in 70 (9.5%) strains. Eighteen different eae genotypes were identified in 62 eae-positive STEC strains with the nucleotide identities ranging from 86.01% to 99.97%. Among which, seven genotypes were newly identified in this study. The eighteen eae genotypes can be categorized into five eae subtypes, namely β1, γ1, ε1, ζ3 and θ. Associations between eae subtypes/genotypes and serotypes as well as origins of strains were observed in this study. Strains belonging to serotypes O26:H11, O103:H2, O111:H8 are associated with particular eae subtypes, i.e., β1, ε1, θ, respectively. Most strains from diarrheal patients (7/9, 77.8%) carried eae-β1 subtype, while most isolates from cattle (23/26, 88.5%) carried eae-ζ3 subtype. This study demonstrated a genetic diversity of eae gene in non-O157 STEC strains from different sources in China.

The European Union One Health 2018 Zoonoses Report

This report of the European Food Safety Authority and the European Centre for Disease Prevention and Control presents the results of zoonoses monitoring activities carried out in 2018 in 36 European countries (28 Member States (MS) and 8 non‐MS). The first and second most commonly reported zoonoses in humans were campylobacteriosis and salmonellosis, respectively. The European Union (EU) trend for confirmed human cases of these two diseases was stable during 2014–2018. The proportion of human salmonellosis cases due to Salmonella Enteritidis was at the same level in 2018 as in 2017. Of the 27 reporting MS, 16 met all Salmonella reduction targets for poultry, whereas 11 MS failed meeting at least one. The EU flock prevalence of target Salmonella serovars in breeding hens, laying hens, broilers and fattening turkeys decreased during recent years but stalled in breeding turkeys. Salmonella results from Competent Authorities for pig carcasses and for poultry tested through National Control Programmes were more frequently positive compared with food business operators. Shiga toxin‐producing Escherichia coli (STEC) infections in humans were the third most commonly reported zoonosis in the EU and increased from 2014 to 2018. Yersiniosis was the fourth most frequently reported zoonosis in humans in 2018 with a stable trend in 2014–2018. The number of reported confirmed listeriosis cases further increased in 2018, despite Listeria rarely exceeding the EU food safety limit tested in ready‐to‐eat food. In total, 5,146 food‐ and waterborne outbreaks were reported. Salmonella was the most commonly detected agent with S. Enteritidis causing one in five outbreaks. Salmonella in eggs and egg products was the highest risk agent/food pair. A large increase of human West Nile virus infections was reported in 2018. The report further updates on bovine tuberculosis, Brucella, Trichinella, Echinococcus, Toxoplasma, rabies, Coxiella burnetii (Q fever) and tularaemia.

Bimodal Response to Shiga Toxin 2 Subtypes Results from Relatively Weak Binding to the Target Cell

There are two major antigenic forms of Shiga toxin (Stx), Stx1 and Stx2, which bind the same receptor and act on the same target but nonetheless differ in potency. Stx1a is more toxic to cultured cells, but Stx2 subtypes are more potent in animal models. To understand this phenomenon in cultured cells, we used a system that combines flow cytometry with a fluorescent reporter to monitor the Stx-induced inhibition of protein synthesis in single cells. We observed that Vero cells intoxicated with Stx1a behave differently than those intoxicated with Stx2 subtypes: cells challenged with Stx1a exhibited a population-wide loss of protein synthesis, while cells exposed to Stx2a or Stx2c exhibited a dose-dependent bimodal response in which one subpopulation of cells was unaffected (i.e., no loss of protein synthesis). Cells challenged with a hybrid toxin containing the catalytic subunit of Stx1a and the cell-binding subunit of Stx2a also exhibited a bimodal response to intoxication, while cells challenged with a hybrid toxin containing the catalytic subunit of Stx2a and the cell-binding subunit of Stx1a exhibited a population-wide loss of protein synthesis. Other experiments further supported a primary role for the subtype of the B subunit in the outcome of host-Stx interactions. Our collective observations indicate that the bimodal response to Stx2 subtypes is due to relatively weak binding between Stx2 and the host cell that reduces the total functional pool of Stx2 in comparison to that of Stx1a. This explains, in part, the molecular basis for the differential cellular toxicity between Stx1a and Stx2 subtypes.

Point-of-Care Strategies for Detection of Waterborne Pathogens

Waterborne diseases that originated due to pathogen microorganisms are emerging as a serious global health concern. Therefore, rapid, accurate, and specific detection of these microorganisms (i.e., bacteria, viruses, protozoa, and parasitic pathogens) in water resources has become a requirement of water quality assessment. Significant research has been conducted to develop rapid, efficient, scalable, and affordable sensing techniques to detect biological contaminants. State-of-the-art technology-assisted smart sensors have improved features (high sensitivity and very low detection limit) and can perform in a real-time manner. However, there is still a need to promote this area of research, keeping global aspects and demand in mind. Keeping this view, this article was designed carefully and critically to explore sensing technologies developed for the detection of biological contaminants. Advancements using paper-based assays, microfluidic platforms, and lateral flow devices are discussed in this report. The emerging recent trends, mainly point-of-care (POC) technologies, of water safety analysis are also discussed here, along with challenges and future prospective applications of these smart sensing technologies for water health diagnostics.

Synthesis and Application of Silver Nanoparticles (Ag NPs) for the Prevention of Infection in Healthcare Workers

Silver is easily available and is known to have microbicidal effect; moreover, it does not impose any adverse effects on the human body. The microbicidal effect is mainly due to silver ions, which have a wide antibacterial spectrum. Furthermore, the development of multidrug-resistant bacteria, as in the case of antibiotics, is less likely. Silver ions bind to halide ions, such as chloride, and precipitate; therefore, when used directly, their microbicidal activity is shortened. To overcome this issue, silver nanoparticles (Ag NPs) have been recently synthesized and frequently used as microbicidal agents that release silver ions from particle surface. Depending on the specific surface area of the nanoparticles, silver ions are released with high efficiency. In addition to their bactericidal activity, small Ag NPs (<10 nm in diameter) affect viruses although the microbicidal effect of silver mass is weak. Because of their characteristics, Ag NPs are useful countermeasures against infectious diseases, which constitute a major issue in the medical field. Thus, medical tools coated with Ag NPs are being developed. This review outlines the synthesis and utilization of Ag NPs in the medical field, focusing on environment-friendly synthesis and the suppression of infections in healthcare workers (HCWs).

Draft Genome Sequences of Shiga Toxin-Producing Escherichia coli O157:H7 Strains Recovered from a Major Production Region for Leafy Greens in California

Shiga toxin-producing Escherichia coli O157:H7 is a foodborne pathogen and is responsible for outbreaks of human gastroenteritis. This report documents the draft genome sequences of nine O157:H7 cattle strains, which were identified to be PCR positive for a Shiga toxin gene but displayed different levels of functional toxin activity.

Shiga toxin-producing Escherichia coli (STEC) isolated from fecal samples of African dromedary camels

Shiga toxin-producing Escherichia coli (STEC) cause gastrointestinal illnesses including non-bloody or bloody diarrhoea, haemorrhagic colitis (HC), and the haemolytic uremic syndrome (HUS). To investigate the occurrence of STEC among grazing dromedaries from Kenya, E. coli isolated from fecal matter collected from 163 dromedaries on a large ranch were screened for the presence of stx1 and stx2. STEC strains were isolated and serotyped. Isolates were subjected to PCR for the subtyping of stx genes and for the detection of eae and ehx. In addition, whole genome sequencing (WGS) was carried out to detect further virulence genes and to determine the multilocus sequence types (MLST). Antimicrobial resistance profiles were determined by disk diffusion. STEC was isolated from 20 (12.3%) of the fecal samples. Thereof, nine (45%) isolates were STEC O156:H25, three (15%) isolates typed STEC O43:H2. The remaining isolates occurred as single serotypes or were O non-typeable. Eleven (55%) of the isolates harboured stx2a, nine (45%) eae, and 14 (70%) ehx, respectively. WGS revealed the presence of iss in 16 (80%), subAB in four (20%) and astA in two (10%) of the isolates, Furthermore, espA, tccP, nleA, nleB, tccP, and tir were found exclusively among STEC O156:H25. Eleven different sequence types (ST) were detected. The most prominent was ST300/ST5343, which comprised STEC O156:H25. All STEC isolates were pan susceptible to a panel of 16 antimicrobial agents. Overall, the results indicate that dromedary camels in Kenya may be reservoirs of STEC, including serotypes possessing virulence markers associated to disease in humans, such as STEC O156:H25. STEC in camels may represent a health hazard for humans with close contact to camels or to consumers of camel derived foodstuffs, such as unpasteurised camel milk.

Sepsis-associated disseminated intravascular coagulation and its differential diagnoses

Disseminated intravascular coagulation (DIC) is a common complication in sepsis. Since DIC not only promotes organ dysfunction but also is a strong prognostic factor, its diagnosis at the earliest possible timing is important. Thrombocytopenia is often present in patients with DIC but can also occur in a number of other critical conditions. Of note, many of the rare thrombocytopenic diseases require prompt diagnoses and specific treatments. To differentiate these diseases correctly, the phenotypic expressions must be considered and the different disease pathophysiologies must be understood. There are three major players in the background characteristics of thrombocytopenia: platelets, the coagulation system, and vascular endothelial cells. For example, the activation of coagulation is at the core of the pathogenesis of sepsis-associated DIC, while platelet aggregation is the essential mechanism in thrombotic thrombocytopenic purpura and endothelial damage is the hallmark of hemolytic uremic syndrome. Though each of the three players is important in all thrombocytopenic diseases, one of the three dominant players typically establishes the individual features of each disease. In this review, we introduce the pathogeneses, symptoms, diagnostic measures, and recent therapeutic advances for the major diseases that should be immediately differentiated from DIC in sepsis.

Engineering of receptor-binding proteins in bacteriophages and phage tail-like bacteriocins

Bacteriophages and phage tail-like bacteriocins (PTLBs) rely on receptor-binding proteins (RBPs) located in tail fibers or spikes for an initial and specific interaction with susceptible bacteria. Bacteriophages kill bacteria through a lytic, replicative cycle, whereas PTLBs kill the target through membrane depolarization in a single hit mechanism. Extensive efforts in the engineering of RBPs of both phages and PTLBs have been undertaken to obtain a greater understanding of the structural organization of RBPs. In addition, a major goal of engineering RBPs of phages and PTLBs is the production of antibacterials with a customized spectrum. Swapping of the RBP of phages and PTLBs results in a shift in activity spectrum in accordance with the spectrum of the new RBP. The engineering of strictly virulent phages with new RBPs required significant technical advances in the past decades, whereas the engineering of RBPs of PTLBs relied on the traditional molecular techniques used for the manipulation of bacteria and was thus relatively straightforward. While phages and PTLBs share their potential for specificity tuning, specific features of phages such as their lytic killing mechanism, their self-replicative nature and thus different pharmacokinetics and their potential to co-evolve are clear differentiators compared with PTLBs in terms of their antibacterial use.