Mechanisms involved in the adaptation of Escherichia coli O157:H7 to the host intestinal microenvironment

Host adaptation of pathogens may increase intra- and interspecies transmission. We showed previously that the passage of a clinically isolated enterohemorrhagic Escherichia coli (EHEC) O157 strain (125/99) through the gastrointestinal tract of mice increases its pathogenicity in the same host. In this work, we aimed to elucidate the underlying mechanism(s) involved in the patho-adaptation of the stool-recovered (125RR) strain. We assessed the global transcription profile by microarray and found almost 100 differentially expressed genes in 125RR strain compared with 125/99 strain. We detected an overexpression of Type Three Secretion System (TTSS) proteins at the mRNA and protein levels and demonstrated increased adhesion to epithelial cell lines for the 125RR strain. Additional key attributes of the 125RR strain were: increased motility on semisolid agar, which correlated with an increased fliC mRNA level; reduced Stx2 production at the mRNA and protein levels; increased survival at pH 2.5, as determined by acid resistance assays. We tested whether the overexpression of the LEE-encoded regulator (ler) in trans in the 125/99 strain could recreate the increased pathogenicity observed in the 125RR strain. As anticipated ler overexpression led to increased expression of TTSS proteins and bacterial adhesion to epithelial cells in vitro but also increased mortality and intestinal colonization in vivo. We conclude that this host-adaptation process required changes in several mechanisms that improved EHEC O157 fitness in the new host. The research highlights some of the bacterial mechanisms required for horizontal transmission of these zoonotic pathogens between their animal and human populations.

Comparative Pathogenicity of Wildlife and Bovine Escherichia coli O157:H7 Strains in Experimentally Inoculated Neonatal Jersey Calves

Shiga toxin-producing Escherichia coli, like E. coli O157:H7, are important human and animal pathogens. Naturally-acquired E. coli O157:H7 infections occur in numerous species but, particularly, cattle have been identified as a significant reservoir for human cases. E. coli O157:H7 are isolated from a number of domestic and wild animals, including rodents that share a living space with cattle. These Shiga toxin-producing E. coli O157:H7 strains can be highly virulent in humans, but little is known about the sequelae of interspecies transfer. In a group of neonatal calves, we determined the differences in colonization patterns and lesions associated with infection using either a wildlife or bovine E. coli O157:H7 strain. In calves challenged with the wildlife E. coli O157:H7 strain, the large (descending) colon was solely colonized, which differed substantially from the calves inoculated with the bovine E. coli O157:H7 strain, where the spiral colon was the principal target of infection. This study also demonstrated that while both interspecies- and intraspecies-derived E. coli O157:H7 can infect young calves, the distribution and severity differs.

Quantitative Proteomic Analysis Reveals Changes in the Benchmark Corynebacterium pseudotuberculosis Biovar Equi Exoproteome after Passage in a Murine Host

Corynebacterium pseudotuberculosis biovar equi is the etiologic agent of ulcerative lymphangitis. To investigate proteins that could be related to the virulence of this pathogen, we combined an experimental passage process using a murine model and high-throughput proteomics with a mass spectrometry, data-independent acquisition (LC-MS^E) approach to identify and quantify the proteins released into the supernatants of strain 258_equi. To our knowledge, this approach allowed characterization of the exoproteome of a C. pseudotuberculosis equi strain for the first time. Interestingly, the recovery of this strain from infected mouse spleens induced a change in its virulence potential, and it became more virulent in a second infection challenge. Proteomic screening performed from culture supernatant of the control and recovered conditions revealed 104 proteins that were differentially expressed between the two conditions. In this context, proteomic analysis of the recovered condition detected the induction of proteins involved in bacterial pathogenesis, mainly related to iron uptake. In addition, KEGG enrichment analysis showed that ABC transporters, bacterial secretion systems and protein export pathways were significantly altered in the recovered condition. These findings show that secretion and secreted proteins are key elements in the virulence and adaptation of C. pseudotuberculosis. Collectively, bacterial pathogenesis-related proteins were identified that contribute to the processes of adherence, intracellular growth and evasion of the immune system. Moreover, this study enhances our understanding of the factors that may influence the pathogenesis of C. pseudotuberculosis.

A shift in the virulence potential of Corynebacterium pseudotuberculosis biovar ovis after passage in a murine host demonstrated through comparative proteomics

Background

Corynebacterium pseudotuberculosis biovar ovis, a facultative intracellular pathogen, is the etiologic agent of caseous lymphadenitis in small ruminants. During the infection process, C. pseudotuberculosis changes its gene expression to resist different types of stresses and to evade the immune system of the host. However, factors contributing to the infectious process of this pathogen are still poorly documented. To better understand the C. pseudotuberculosis infection process and to identify potential factors which could be involved in its virulence, experimental infection was carried out in a murine model using the strain 1002_ovis and followed by a comparative proteomic analysis of the strain before and after passage.

Results

The experimental infection assays revealed that strain 1002_ovis exhibits low virulence potential. However, the strain recovered from the spleen of infected mice and used in a new infection challenge showed a dramatic change in its virulence potential. Label-free proteomic analysis of the culture supernatants of strain 1002_ovis before and after passage in mice revealed that 118 proteins were differentially expressed. The proteome exclusive to the recovered strain contained important virulence factors such as CP40 proteinase and phospholipase D exotoxin, the major virulence factor of C. pseudotuberculosis. Also, the proteome from recovered condition revealed different classes of proteins involved in detoxification processes, pathogenesis and export pathways, indicating the presence of distinct mechanisms that could contribute in the infectious process of this pathogen.

Conclusions

This study shows that C. pseudotuberculosis modifies its proteomic profile in the laboratory versus infection conditions and adapts to the host context during the infection process. The screening proteomic performed us enable identify known virulence factors, as well as potential proteins that could be related to virulence this pathogen. These results enhance our understanding of the factors that might influence in the virulence of C. pseudotuberculosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-0925-6) contains supplementary material, which is available to authorized users.

Development of camelid single chain antibodies against Shiga toxin type 2 (Stx2) with therapeutic potential against Hemolytic Uremic Syndrome (HUS)

Shiga toxin (Stx)-producing Escherichia coli (STEC) infections are implicated in the development of the life-threatening Hemolytic Uremic Syndrome (HUS). Despite the magnitude of the social and economic problems caused by STEC infections, no licensed vaccine or effective therapy is presently available for human use. Single chain antibodies (VHH) produced by camelids exhibit several advantages in comparison with conventional antibodies, making them promising tools for diagnosis and therapy. In the present work, the properties of a recently developed immunogen, which induces high affinity and protective antibodies against Stx type 2 (Stx2), were exploited to develop VHHs with therapeutic potential against HUS. We identified a family of VHHs against the B subunit of Stx2 (Stx2B) that neutralize Stx2 in vitro at subnanomolar concentrations. One VHH was selected and was engineered into a trivalent molecule (two copies of anti-Stx2B VHH and one anti-seroalbumin VHH). The resulting molecule presented extended in vivo half-life and high therapeutic activity, as demonstrated in three different mouse models of Stx2-toxicity: a single i.v. lethal dose of Stx2, several i.v. incremental doses of Stx2 and intragastrical STEC infection. This simple antitoxin agent should offer new therapeutic options for treating STEC infections to prevent or ameliorate HUS outcome.

Animal Models of Enterohemorrhagic Escherichia coli Infection

The first major outbreaks caused by enterohemorrhagic Escherichia coli (EHEC) raised public and medical awareness of the risks associated with acquiring this potentially deadly infection. The widespread presence of these organisms in the environment, the severity of the clinical sequelae, and the lack of treatment options and effective preventive measures demand that we obtain a better understanding of how this group of organisms cause disease. Animal models allow study of the processes and factors that contribute to disease and, as such, form a valuable tool in the repertoire of infectious disease researchers. Yet despite more than 30 years of research, it seems that no single model host reproduces the full spectrum of clinical disease induced by EHEC in humans. In the first part of this review, a synopsis of what is known about EHEC infections is garnered from human outbreaks and biopsy specimens. The main features and limitations of EHEC infection models that are based on the three most commonly used species (pigs, rabbits, and mice) are described within a historical context. Recent advances are highlighted, and a brief overview of models based on other species is given. Finally, the impact of the host on moderating EHEC infection is considered in light of growing evidence for the need to consider the biology and virulence strategies of EHEC in the context of its niche within the intestine.

Strain-dependent cellular immune responses in cattle following Escherichia coli O157:H7 colonization

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 causes hemorrhagic diarrhea and potentially fatal renal failure in humans. Ruminants are considered to be the primary reservoir for human infection. Vaccines that reduce shedding in cattle are only partially protective, and their underlying protective mechanisms are unknown. Studies investigating the response of cattle to colonization generally focus on humoral immunity, leaving the role of cellular immunity unclear. To inform future vaccine development, we studied the cellular immune responses of cattle during EHEC O157:H7 colonization. Calves were challenged either with a phage type 21/28 (PT21/28) strain possessing the Shiga toxin 2a (Stx2a) and Stx2c genes or with a PT32 strain possessing the Stx2c gene only. T-helper cell-associated transcripts at the terminal rectum were analyzed by reverse transcription-quantitative PCR (RT-qPCR). Induction of gamma interferon (IFN-γ) and T-bet was observed with peak expression of both genes at 7 days in PT32-challenged calves, while upregulation was delayed, peaking at 21 days, in PT21/28-challenged calves. Cells isolated from gastrointestinal lymph nodes demonstrated antigen-specific proliferation and IFN-γ release in response to type III secreted proteins (T3SPs); however, responsiveness was suppressed in cells isolated from PT32-challenged calves. Lymph node cells showed increased expression of the proliferation marker Ki67 in CD4(+) T cells from PT21/28-challenged calves, NK cells from PT32-challenged calves, and CD8(+) and γδ T cells from both PT21/28- and PT32-challenged calves following ex vivo restimulation with T3SPs. This study demonstrates that cattle mount cellular immune responses during colonization with EHEC O157:H7, the temporality of which is strain dependent, with further evidence of strain-specific immunomodulation.

Advances in pathogenesis and therapy of hemolytic uremic syndrome caused by Shiga toxin-2

Shiga toxin (Stx) producing Escherichia coli (STEC) is responsible to bloody diarrhea (hemorrhagic colitis) and the hemolytic uremic syndrome (HUS). STEC strains carry inducible lambda phages integrated into their genomes that encode Stx 1 and/or 2, with several allelic variants each one. O157:H7 is the serotype that was documented in the vast majority of HUS cases although non-O157 serotypes have been increasingly reported to account for HUS cases. However, the outbreak that occurred in central Europe during late spring of 2011 showed that the pathogen was E. coli O104:H4. More than 4,000 persons were infected mainly in Germany, and it produced more than 900 cases of HUS resulting in 54 deaths. E. coli O104:H4 is a hybrid organism that combines some of the virulence genes of STEC and enteroaggregative E. coli specially production of Stx2 and the adherence mechanisms to intestinal epithelium. The differences in the epidemiology and presentation of E. coli pathogen meant a challenge for public health and scientific research to increase the knowledge of HUS-pathophysiology and to improve available therapies to treat HUS.

Immunization with a chimera consisting of the B subunit of Shiga toxin type 2 and brucella lumazine synthase confers total protection against Shiga toxins in mice

The striking feature of enterohemorrhagic Escherichia coli (EHEC) infections is the production of Shiga toxins (Stx) implicated in the development of the life-threatening hemolytic uremic syndrome. Despite the magnitude of the social impact of EHEC infections, no licensed vaccine or effective therapy is available for human use. One of the biggest challenges is to develop an effective and safe immunogen to ensure nontoxicity, as well as a strong input to the immune system to induce long-lasting, high-affinity Abs with anti-Stx-neutralizing capacity. The enzyme lumazine synthase from Brucella spp. (BLS) is a highly stable dimer of pentamers and a scaffold with enormous plasticity on which to display foreign Ags. Taking into account the advantages of BLS and the potential capacity of the B subunit of Stx2 to induce Abs that prevent Stx2 toxicity by blocking its entrance into the host cells, we engineered a new immunogen by inserting the B subunit of Stx2 at the amino termini of BLS. The resulting chimera demonstrated a strong capacity to induce a long-lasting humoral immune response in mice. The chimera induced Abs with high neutralizing capacity for Stx2 and its variants. Moreover, immunized mice were completely protected against i.v. Stx2 challenge, and weaned mice receiving an oral challenge with EHEC were completely protected by the transference of immune sera. We conclude that this novel immunogen represents a promising candidate for vaccine or Ab development with preventive or therapeutic ends, for use in hemolytic uremic syndrome-endemic areas or during future outbreaks caused by pathogenic strains of Stx-producing E. coli.