Effects of subinhibitory concentrations of antimicrobial agents on Escherichia coli O157:H7 Shiga toxin release and role of the SOS response

Genome Sequence Analysis and Characterization of Shiga Toxin 2 Production by Escherichia coli O157:H7 Strains Associated With a Laboratory Infection

A laboratory-acquired E. coli O157:H7 infection with associated severe sequelae including hemolytic uremic syndrome occurred in an individual working in the laboratory with a mixture of nalidixic acid-resistant (Nal^R) O157:H7 mutant strains in a soil-biochar blend. The patient was hospitalized and treated with an intravenous combination of metronidazole and levofloxacin. The present study investigated the source of this severe laboratory acquired infection and further examined the influence of the antibiotics used during treatment on the expression and production of Shiga toxin. Genomes of two Stx_2a-and eae-positive O157:H7 strains isolated from the patient's stool were sequenced along with two pairs of the wt strains and their derived Nal^R mutants used in the laboratory experiments. High-resolution SNP typing determined the strains' individual genetic relatedness and unambiguously identified the two laboratory-derived Nal^R mutant strains as the source of the researcher's life-threatening disease, rather than a conceivable ingestion of unrelated O157:H7 isolates circulating at the same time. It was further confirmed that in sublethal doses, the antibiotics increased toxin expression and production. Our results support a simultaneous co-infection with clinical strains in the laboratory, which were the causative agents of previous O157:H7 outbreaks, and further that the administration of antibiotics may have impacted the outcome of the infection.

Azithromycin resistance in Shiga-toxin Producing Escherichia coli in France between 2004 and 2020 and detection of mef(C)-mph(G) genes

We described and characterized Shiga-toxin-producing Escherichia coli (STEC) strains with high levels of resistance to azithromycin isolated in France, between 2004 and 2020. Nine of 1715 (0.52%) STEC strains were resistant to azithromycin, with an increase since 2017. One isolate carried a plasmid-borne mef(C)-mph(G) genes association, described here for the first time in E. coli. Azithromycin resistance, although rare, needs consideration as this treatment may be useful in case of STEC infection.

Maximum levels of cross-contamination for 24 antimicrobial active substances in non-target feed. Part 4: β-Lactams: amoxicillin and penicillin V

The specific concentrations of amoxicillin and penicillin V in non-target feed for food-producing animals, below which there would not be an effect on the emergence of, and/or selection for, resistance in bacteria relevant for human and animal health, as well as the specific antimicrobial concentrations in feed which have an effect in terms of growth promotion/increased yield were assessed by EFSA in collaboration with EMA. Details of the methodology used for this assessment, associated data gaps and uncertainties, are presented in a separate document. To address antimicrobial resistance, the Feed Antimicrobial Resistance Selection Concentration (FARSC) model developed specifically for the assessment was applied. However, due to the lack of data on the parameters required to calculate the FARSC, it was not possible to conclude the assessment until further experimental data become available. To address growth promotion, data from scientific publications obtained from an extensive literature review were used. Levels in feed that showed to have an effect on growth promotion/increased yield were reported for amoxicillin, whilst for penicillin V no suitable data for the assessment were available. It was recommended to carry out studies to generate the data that are required to fill the gaps which prevented the calculation of the FARSC for these two antimicrobials.

Antibiotic-mediated expression analysis of Shiga toxin 1 and 2 in multi-drug-resistant Shiga toxigenic Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) is an important foodborne pathogens, known to cause enteric infections especially diarrhea, mainly attributed to Shiga toxins (Stxs). The use of certain antibiotics for treating this infection is controversial, owing to an increased risk for producing Stxs (Stx 1 and Stx 2). Increased antibiotic resistance is also thought to be involved in the pathogenesis of STEC diseases. The purpose of this study was to analyze the effects of antibiotics on induction of Stx 1 and Stx 2 in clinical STEC isolates and to investigate the relationships between increased resistance and Stx production. Fifteen clinical isolates were treated with sub minimum inhibitory concentrations (Sub MIC) of clinically used antibiotics (ciprofloxacin, fosfomycin, tigecycline, and meropenem), and the changes in expression levels of stx1 and stx2 genes were estimated using qRT-PCR. The expressions of Shiga toxins were found to be increased up to 6.5- and eightfold under ciprofloxacin and tigecycline Sub MIC, respectively. Fosfomycin had weak induction effect of up to twofold, whereas meropenem had the weakest influence on such expression. Resistant isolates were found to be more prone to increased expression of toxins.

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.

Natural and synthetic antimicrobials reduce adherence of enteroaggregative and enterohemorrhagic Escherichia coli to epithelial cells

Adherence of bacteria to the human intestinal mucosa can facilitate their internalization and the development of pathological processes. Escherichia coli O104:H4 is considered a hybrid strain (enteroaggregative hemorrhagic E. coli [EAHEC]), sharing virulence factors found in enterohemorrhagic (EHEC), and enteroaggregative (EAEC) E. coli pathotypes. The objective of this study was to analyze the effects of natural and synthetic antimicrobials (carvacrol, oregano extract, brazilin, palo de Brasil extract, and rifaximin) on the adherence of EHEC O157:H7, EAEC 042, and EAHEC O104:H4 to HEp-2 cells and to assess the expression of various genes involved in this process. Two concentrations of each antimicrobial that did not affect (p≤0.05) bacterial viability or damage the bacterial membrane integrity were used. Assays were conducted to determine whether the antimicrobials alter adhesion by affecting bacteria and/or alter adhesion by affecting the HEp-2 cells, whether the antimicrobials could detach bacteria previously adhered to HEp-2 cells, and whether the antimicrobials could modify the adherence ability exhibited by the bacteria for several cycles of adhesion assays. Giemsa stain and qPCR were used to assess the adhesion pattern and gene expression, respectively. The results showed that the antimicrobials affected the adherence abilities of the bacteria, with carvacrol, oregano extract, and rifaximin reducing up to 65% (p≤0.05) of E. coli adhered to HEp-2 cells. Carvacrol (10 mg/ml) was the most active compound against EHAEC O104:H4, even altering its aggregative adhesion pattern. There were changes in the expression of adhesion-related genes (aggR, pic, aap, aggA, and eae) in the bacteria and oxidative stress-related genes (SOD1, SOD2, CAT, and GPx) in the HEp-2 cells. In general, we demonstrated that carvacrol, oregano extract, and rifaximin at sub-minimal bactericidal concentrations interfere with target sites in E. coli, reducing the adhesion efficiency.

"Effect of Subinhibitory Concentrations of Some Antibiotics and Low Doses of Gamma Radiation on the Cytotoxicity and Expression of Colibactin by an Uropathogenic Escherichia coli isolate"

Colibactin and cytotoxic necrotizing factor 1 (Cnf 1) are cyclomodulins secreted by uropathogenic E. coli. In this study, uropathogenic E. coli expressing colibactin and Cnf 1 was exposed to antibiotics subMICs and gamma radiation to investigate their effects on its cytotoxicity and expression of colibactin. The test isolate was exposed to three subMIC levels of levofloxacin, ciprofloxacin, trimethoprim/sulfamethoxazole and ceftriaxone and irradiated with gamma rays at 10 and 24.4 Gy. The cytotoxicity for either antibiotic or gamma rays treated cultures was measured using MTT assay and the expression of colibactin encoding genes was determined by RT-PCR. Treatment with fluoroquinolones nearly abolished the cytotoxicity of E. coli isolate and significantly downregulated clbA gene expression at the tested subMICs (P ≤ 0.05) while trimethoprim/sulfamethoxazole treated cultures exerted significant downregulation of clbA and clbQ genes at 0.5 MIC only (P ≤ 0.05). Ceftriaxone treated cultured exhibited reduction in the cytotoxicity and insignificant effects on expression of clbA, clbQ and clbM genes. On contrast, significant upregulation in the expression of clbA and clbQ genes was observed in irradiated cultures (P ≤ 0.05). Fluoroquinolones reduced both the cytotoxicity of UPEC isolate and colibactin expression at different subMICs while ceftriaxone at subMICs failed to suppress the expression of genotoxin, colibactin, giving an insight to the risks associated upon their choice for UTI treatment. Colibactin expression was enhanced by gamma irradiation at doses resembling these received during pelvic radiotherapy which might contribute to post-radiotherapy complications.

Overall changes in the transcriptome of Escherichia coli O26:H11 induced by a subinhibitory concentration of ciprofloxacin

AIMS

The goal was to explore the effects of subinhibitory concentration (SIC) (0·5 MIC = 20 µg l^-1 ) of ciprofloxacin on the transcriptome of enterohaemorrhagic Escherichia coli O26:H11 isolate by 60 minutes of exposure.

MATERIALS AND RESULTS

We used a combination of comparative genomic and transcriptomic (RNAseq) analyses. The whole genome of the E. coli O26:H11 #30934 strain of bovine origin was sequenced and assembled. This genome was next used as reference for the differential gene expression analysis. A whole-genome-based analysis of 36 publicly available E. coli O26:H11 genomes was performed to define the core and the accessory transcriptome of E. coli O26:H11. Using RNAseq and RT-qPCR analysis we observed overexpression of the SOS response and of T3SS effectors, together with the inhibition of specific motility-associated genes. Among the large set of transposases present, only three were activated, suggesting moderate transposition of genes with low doses of ciprofloxacin. Our results illustrated that transcriptional repressors, such as the CopG family protein, belonging to the core genome of E. coli O26:H11, are altered in response to fluoroquinolone exposure. The gene ontology enrichment analysis showed SIC of ciprofloxacin induced binding functions and catalytic activities, including mostly transferase and hydrolase proteins. The amino acid pathways involved in metabolic processes were significantly enhanced after the treatment.

CONCLUSIONS

Although the core genome of E. coli O26:H11 constituted only 54·5% of the whole genome, we demonstrated that most differentially expressed genes were associated with the core genome of E. coli O26:H11, and that effects on the mobile genetic element, phage, and plasmid-related genes were rare.

SIGNIFICANCE AND IMPACT OF THE STUDY

For the first time the effect of low dose of ciprofloxacin on the core transcriptome of E. coli O26:H11 was described. The effects on the main biological functions and protein classes including transcriptional regulators were illustrated.

Treatment Strategies for Infections With Shiga Toxin-Producing Escherichia coli

Infections with Shiga toxin-producing Escherichia coli (STEC) cause outbreaks of severe diarrheal disease in children and the elderly around the world. The severe complications associated with toxin production and release range from bloody diarrhea and hemorrhagic colitis to hemolytic-uremic syndrome, kidney failure, and neurological issues. As the use of antibiotics for treatment of the infection has long been controversial due to reports that antibiotics may increase the production of Shiga toxin, the recommended therapy today is mainly supportive. In recent years, a variety of alternative treatment approaches such as monoclonal antibodies or antisera directed against Shiga toxin, toxin receptor analogs, and several vaccination strategies have been developed and evaluated in vitro and in animal models. A few strategies have progressed to the clinical trial phase. Here, we review the current understanding of and the progress made in the development of treatment options against STEC infections and discuss their potential.

Identification of Antibiotics That Diminish Disease in a Murine Model of Enterohemorrhagic Escherichia coli Infection

Infections with enterohemorrhagic Escherichia coli (EHEC) cause disease ranging from mild diarrhea to hemolytic-uremic syndrome (HUS) and are the most common cause of renal failure in children in high-income countries. The severity of the disease derives from the release of Shiga toxins (Stx). The use of antibiotics to treat EHEC infections is generally avoided, as it can result in increased stx expression. Here, we systematically tested different classes of antibiotics and found that their influence on stx expression and release varies significantly. We assessed a selection of these antibiotics in vivo using the Citrobacter rodentium ϕstx _2dact mouse model and show that stx _2d-inducing antibiotics resulted in weight loss and kidney damage despite clearance of the infection. However, several non-Stx-inducing antibiotics cleared bacterial infection without causing Stx-mediated pathology. Our results suggest that these antibiotics might be useful in the treatment of EHEC-infected human patients and decrease the risk of HUS development.

Enterohaemorrhagic Escherichia coli O121:H19 acquired an extended-spectrum β-lactamase gene during the development of an outbreak in two nurseries

Enterohaemorrhagic Escherichia coli (EHEC) is an important human pathogen worldwide. Although serotype O157 is currently the most dominant and important EHEC strain, serotypes O26, O111, O91, O103 and O121 are also recognized as serious pathogens that affect public health. EHEC outbreaks often occur in nurseries and elderly care facilities. In 2012, a nursery outbreak of EHEC O121 occurred during which the bacterium acquired a plasmid-borne extended-spectrum β-lactamase (ESBL) gene. ESBL-producing E. coli O86 was concurrently isolated from one of the EHEC patients. Therefore, we investigated the isolates by whole-genome sequence (WGS) analysis to elucidate the transmission dynamics of the EHEC strains and the ESBL plasmid. According to WGS-based phylogeny, all 17 EHEC O121 isolates were clonal, while E. coli O86 was genetically distant from the EHEC O121 isolates. The complete sequence of an ESBL plasmid encoding the CTX-M-55 β-lactamase was determined using S1-PFGE bands, and subsequent mapping of the WGS reads confirmed that the plasmid sequences from EHEC O121 and E. coli O86 were identical. Furthermore, conjugation experiments showed that the plasmid was capable of conjugative transfer. These results support the hypothesis that EHEC O121 acquired an ESBL-producing plasmid from E. coli O86 during the outbreak. This report demonstrates the importance of implementing preventive measures during EHEC outbreaks to control both secondary infection and the spread of antimicrobial resistance factors.

The disparate effects of bacteriophages on antibiotic-resistant bacteria

Faced with the crisis of multidrug-resistant bacteria, bacteriophages, viruses that infect and replicate within bacteria, have been reported to have both beneficial and detrimental effects with respect to disease management. Bacteriophages (phages) have important ecological and evolutionary impacts on their bacterial hosts and have been associated with therapeutic use to kill bacterial pathogens, but can lead to the transmission of antibiotic resistance. Although the process known as transduction has been reported for many bacterial species by classic and modern genetic approaches, its contribution to the spread of antibiotic resistance in nature remains unclear. In addition, detailed molecular studies have identified phages residing in bacterial genomes, revealing unexpected interactions between phages and their bacterial hosts. Importantly, antibiotics can induce the production of phages and phage-encoded products, disseminating these viruses and virulence-related genes, which have dangerous consequences for disease severity. These unwanted side-effects of antibiotics cast doubt on the suitability of some antimicrobial treatments and may require new strategies to prevent and limit the selection for virulence. Foremost among these treatments is phage therapy, which could be used to treat many bacterial infectious diseases and confront the pressing problem of antibiotic resistance in pathogenic bacteria. This review discusses the interactions between bacteriophages, antibiotics, and bacteria and provides an integrated perspective that aims to inspire the development of successful antibacterial therapies.

Influences of epigallocatechin gallate and citric acid on Escherichia coli O157:H7 toxin gene expression and virulence-associated stress response

Citric acid and EGCG at their minimum inhibitory concentrations were tested in this study. Logarithmic phase cells of Escherichia coli O157:H7 (ATCC 43895) were exposed to EGCG and citric acid respectively. The results of RT-real time PCR showed that both EGCG and citric acid increased stx2 and oxyR expression and decreased stx1, recA and Q expression. The result of Western blotting for RecA protein further indicated that both EGCG and citric acid decreased RecA production. Both EGCG and citric acid increased the level of intracellular reactive oxygen species and H₂ O₂ production and decreased superoxide dismutase activity. Therefore, EGCG and citric acid might induce stx2 production by increasing oxidative stress response and inhibit stx1 production by suppressing SOS response. In our study, the differential effects of the two antimicrobials were observed. EGCG reduced ompC and rpoS expression. However, citric acid caused an increase in ompC and rpoS expression. Membrane permeability is associated with toxin release. Citric acid increased the outer membrane permeability of E. coli O157:H7. However, the outer membrane of E. coli O157:H7 remained unaffected by EGCG.

SIGNIFICANCE AND IMPACT OF THE STUDY

Shiga toxins are the major virulence factors of Escherichia coli O157:H7. The use of antimicrobials triggering Shiga toxin production is controversial. (-)-epigallocatechin-3-gallate (EGCG) citric acid are often used singly or in combination to prevent micro-organisms in some food products. This study evaluated toxin induction in E. coli O157:H7 in response to EGCG and citric acid and investigated the potential mechanism of action. The findings may contribute to the proper use of EGCG and citric acid as antimicrobials.

Enterohemorrhagic Escherichia coli Hybrid Pathotype O80:H2 as a New Therapeutic Challenge

This emerging clonal group harbors the extraintestinal virulence–associated plasmid pS88 and can induce invasive infections and death.

We describe the epidemiology, clinical features, and molecular characterization of enterohemorrhagic Escherichia coli (EHEC) infections caused by the singular hybrid pathotype O80:H2, and we examine the influence of antibiotics on Shiga toxin production. In France, during 2005–2014, a total of 54 patients were infected with EHEC O80:H2; 91% had hemolytic uremic syndrome. Two patients had invasive infections, and 2 died. All strains carried stx2 (variants stx2a, 2c, or 2d); the rare intimin gene (eae-ξ); and at least 4 genes characteristic of pS88, a plasmid associated with extraintestinal virulence. Similar strains were found in Spain. All isolates belonged to the same clonal group. At subinhibitory concentrations, azithromycin decreased Shiga toxin production significantly, ciprofloxacin increased it substantially, and ceftriaxone had no major effect. Antibiotic combinations that included azithromycin also were tested. EHEC O80:H2, which can induce hemolytic uremic syndrome complicated by bacteremia, is emerging in France. However, azithromycin might effectively combat these infections.

Alterations of growth rate and gene expression levels of UPEC by antibiotics at sub-MIC

The host is the main environment for bacteria, and they also expose to many antibiotics during the treatment of infectious diseases in host body. In this study, it was aimed to investigate possible changes in growth rate and expression levels of three virulence genes (foc/foc, cnf1, and usp) in a uropathogenic E. coli standard strain within the presence of ciprofloxacin, nitrofurantoin, and trimethoprim-sulfamethoxazole. The UPEC C7 strain was grown on tryptic soy broth-TSB (control), TSB + ciprofloxacin, TSB + nitrofurantoin, and TSB + trimethoprim-sulfamethoxazole for determination of both growth rate and gene expression level. Antibiotics were added according to their sub-minimal inhibition concentrations. E-test was used to determine MIC values of antibiotics. Growth changes were measured in absorbance 600 nm during 24-h period. Total RNA isolations were performed after incubation for 24 h at 37 °C. Gene expression levels were determined by quantitative PCR. Tukey's post hoc test was used for statistical analysis. According to absorbance values, it has been shown that only ciprofloxacin and trimethoprim-sulfamethoxazole have lead significant decrease on growth rate. We also detected statistically significant differences in each gene expression levels for all antibiotics via relative quantification analysis. Fold changes in gene expression was found 0.65, 1.42, 0.23 for foc/foc gene; 0.01, 0.01, 2.84 for cnf1 gene; and 0.1, 0.01, 0.01 for usp gene in the presence of ciprofloxacin, nitrofurantoin, and trimethoprim/sulfamethoxazole, respectively. This investigation has shown that antibiotics can play a role as an environmental factor which may determine the pathogenicity of bacteria in vivo.

Genetic Diversity and Antibiotic Resistance of Escherichia coli Isolates from Different Leafy Green Production Systems

Foodborne disease outbreaks linked to contaminated irrigation water and fresh produce are a public health concern. The presence of Escherichia coli isolates from irrigation water and leafy green vegetables in different food production systems (large commercial farms, small-scale farms, and homestead gardens) was investigated. The prevalence of antibiotic resistance and virulence in these isolates was further assessed, and links between water source and irrigated crops were identified using antimicrobial and genotypic analyses. Presumptive E. coli isolates were identified by matrix-assisted laser desorption ionization time-of-flight mass spectroscopy, and identities were confirmed by PCR using the uidA gene. Antimicrobial susceptibility was evaluated with the Kirby Bauer disk diffusion test; the presence of virulence genes was determined with enterobacterial repetitive intergenic consensus PCR assays. Of the 130 E. coli isolates from water (n =60) and leafy green vegetables (n =70), 19 (14.6%) were resistant to one antibiotic (tetracycline) and 92 (70.7%) were resistant to various antibiotics (including ampicillin, cefoxitin, and nalidixic acid). All E. coli isolates were susceptible to ceftriaxone and gentamicin. The virulence gene stx₂ was detected in E. coli isolates from irrigation water (8 [13.3%] of 60 isolates) and cabbages (3 [7.5%] of 40), but the virulence genes eae and stx₁ were not detected in any tested isolates from irrigation water and fresh produce samples. The prevalence of multidrug-resistant E. coli was lower in isolates from GLOBALG.A.P.-certified farms than in isolates from noncertified commercial and small-scale farms and homestead gardens. A link between the E. coli isolates from irrigation water sources and leafy green vegetables was established with phenotypic (antimicrobial) and genotypic (DNA fingerprinting) analyses. However, a link between virulence genes and the prevalence of antimicrobial resistance could not be established.

The role of temperate bacteriophages in bacterial infection

Bacteriophages are viruses that infect bacteria. There are an estimated 10(31) phage on the planet, making them the most abundant form of life. We are rapidly approaching the centenary of their identification, and yet still have only a limited understanding of their role in the ecology and evolution of bacterial populations. Temperate prophage carriage is often associated with increased bacterial virulence. The rise in use of technologies, such as genome sequencing and transcriptomics, has highlighted more subtle ways in which prophages contribute to pathogenicity. This review discusses the current knowledge of the multifaceted effects that phage can exert on their hosts and how this may contribute to bacterial adaptation during infection.

Approaches to treatment of emerging Shiga toxin-producing Escherichia coli infections highlighting the O104:H4 serotype

Shiga toxin-producing Escherichia coli (STEC) are a group of diarrheagenic bacteria associated with foodborne outbreaks. Infection with these agents may result in grave sequelae that include fatality. A large number of STEC serotypes has been identified to date. E. coli serotype O104:H4 is an emerging pathogen responsible for a 2011 outbreak in Europe that resulted in over 4000 infections and 50 deaths. STEC pathogenicity is highly reliant on the production of one or more Shiga toxins that can inhibit protein synthesis in host cells resulting in a cytotoxicity that may affect various organ systems. Antimicrobials are usually avoided in the treatment of STEC infections since they are believed to induce bacterial cell lysis and the release of stored toxins. Some antimicrobials have also been reported to enhance toxin synthesis and production from these organisms. Various groups have attempted alternative treatment approaches including the administration of toxin-directed antibodies, toxin-adsorbing polymers, probiotic agents and natural remedies. The utility of antibiotics in treating STEC infections has also been reconsidered in recent years with certain modalities showing promise.

Effect of rifampicin and gentamicin on Shiga toxin 2 expression level and the SOS response in Escherichia coli O104:H4

BACKGROUND

A novel pathotype, Shiga toxin-producing Escherichia coli O104:H4, was the cause of a severe outbreak that affected European countries, mainly Germany, in 2011. The effect of different regimens of rifampicin and gentamicin were evaluated to determine possible treatment modes for the novel strain, and to evaluate the SOS response and its effect on toxin release.

MATERIALS AND METHODS

Pulsed-field gel electrophoresis (PFGE) was performed on the novel E. coli O104:H4 pathotype and two pre-outbreak E. coli O104:H4 CDC strains. Transcript levels of the stx2 and recA gene (SOS response inducer) were evaluated using quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR) in the novel E. coli O104:H4 samples subjected to different regimens of rifampicin and gentamicin. Consequently, reverse passive latex agglutination (RPLA) was used to determine the Stx2 titers in these samples. Western blot was performed to determine the LexA levels (SOS response repressor) in E. coli O104:H4. The efficacy of treatment with antimicrobial agents was assessed in BALB/c mice.

RESULTS

The outbreak and pre-outbreak strains are closely related as shown by PFGE, which demonstrated slight genomic differences between the three strains. The transcription level of the stx2 gene in the new pathotype was 1.41- and 1.75-fold that of the 2009 EL-2050 and 2009 EL-2071 pre-outbreak strains, respectively. Moreover, the transcription level of the stx2 gene in the new pathotype was substantially decreased as a result of treatment with the different concentrations of the antimicrobial agents, but was enhanced when the antibiotics were administered at two subinhibitory levels. RPLA data were in accordance with the qRT-PCR results. E. coli O104:H4 exposed to gentamicin at both sub-minimum inhibitory concentration (MIC) levels led to high transcription levels of the recA gene and lack of expression of the LexA protein, implying that the SOS response was activated. Rifampicin at both sub-MIC levels resulted in low transcript levels of the recA gene, indicating that the SOS response was not induced. In vivo, the highest survival rate in BALB/c mice was observed in the group that was treated with the minimum bactericidal concentration (MBC) of gentamicin.

CONCLUSION

The use of antimicrobial agents in E. coli O104:H4 infection seems to be effective at the MIC and MBC levels. This provides a promising ground for treatment of E. coli O104:H4.

SOS, the formidable strategy of bacteria against aggressions

The presence of an abnormal amount of single-stranded DNA in the bacterial cell constitutes a genotoxic alarm signal that induces the SOS response, a broad regulatory network found in most bacterial species to address DNA damage. The aim of this review was to point out that beyond being a repair process, SOS induction leads to a very strong but transient response to genotoxic stress, during which bacteria can rearrange and mutate their genome, induce several phenotypic changes through differential regulation of genes, and sometimes acquire characteristics that potentiate bacterial survival and adaptation to changing environments. We review here the causes and consequences of SOS induction, but also how this response can be modulated under various circumstances and how it is connected to the network of other important stress responses. In the first section, we review articles describing the induction of the SOS response at the molecular level. The second section discusses consequences of this induction in terms of DNA repair, changes in the genome and gene expression, and sharing of genomic information, with their effects on the bacteria's life and evolution. The third section is about the fine tuning of this response to fit with the bacteria's 'needs'. Finally, we discuss recent findings linking the SOS response to other stress responses. Under these perspectives, SOS can be perceived as a powerful bacterial strategy against aggressions.

New high-affinity monoclonal antibodies against Shiga toxin 1 facilitate the detection of hybrid Stx1/Stx2 in vivo

BACKGROUND

Shiga toxin-producing E. coli (STEC) are a group of common and potentially deadly intestinal pathogens expressing Shiga toxin (Stx) as a primary virulence factor. Of the two types of Stx, Stx2 is responsible for more severe symptoms during infection, while Stx1 is almost identical to the Shiga toxin from Shigella dysenteriae, a ubiquitous pathogen in developing countries. Although antibodies against Stx1 have been reported, few have reached the affinity needed for assembling highly sensitive immunoassays. Sensitive and affordable immunoassays for Stx1 and Stx2 could help improve detection of STEC in livestock, food, the environment, and in clinical samples resulting in improved food safety and human health.

METHOD AND FINDINGS

Three new monoclonal antibodies (mAbs) against the B subunit of Stx1 were generated using recombinant toxoid Stx1E167Q and hybridoma technology. These new mAbs recognize all subtypes of Stx1, but do not cross-react with any subtype of Stx2. In addition, they exhibited the ability to neutralize Stx1 toxicity in Vero cell assays. An optimized sandwich ELISA using of a pair of these mAbs had a limit of detection of 8.7 pg/mL, which is superior to any existing assay of this kind. Using one of these Stx1 mAbs in concert with Stx2 mAbs, the presence of hybrid Stx1/Stx2 toxin in the culture media of STEC strains that express both Stx1 and Stx2 was demonstrated.

CONCLUSIONS

These new mAbs provide a mix of availability, utility, versatility, and most importantly, increased sensitivity for detection of Stx1. There are numerous potential applications for these mAbs, including low-cost detection assays and therapeutic use. Analysis of hybrid Stx1/2 could provide new insights on the structure, activity, and cellular targets of Shiga toxins.