Auvray, F. | bioRxiv Science

bioRxiv2024

Development of intimin-enriched outer membrane vesicles (OMVs) as a vaccine to control intestinal carriage of Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) are foodborne pathogens causing severe human infections including hemorrhagic colitis and hemolytic uremic syndrome (HUS), particularly in children. Ruminants are the main reservoir of EHEC which colonize their intestinal tract through a mechanism involving the bacterial outer membrane adhesin intimin. Vaccination of cattle has shown efficacy in reducing EHEC O157:H7 shedding in feces. However, most of these vaccines are based on purified proteins and/or require the addition of adjuvants, resulting in expensive vaccines that are not used by breeders. This study introduces the development of a new type of vaccine based on Outer Membrane Vesicles (OMVs) carrying the C-terminal domain of intimin (Int280). A vaccine which combines OMVs carrying luminal Int280 and OMVs displaying surface-exposed Int280 was produced using two addressing systems based on PelB peptide signal and Lpp-OmpA hybrid protein, respectively. This mixed vaccine was tested in a mouse model as a proof of concept using the murine host-specific intestinal pathogen Citrobacter rodentium which shares a similar intimin-based adhesion mechanism with EHEC. Vaccination of mice with OMV-Int280 elicited a strong anti-intimin IgG response. Interestingly, we observed a shortened C. rodentium fecal shedding duration in immunized mice compared to the control group. This OMVs-intimin vaccine therefore represents a promising candidate for the control of EHEC intestinal carriage and fecal shedding in ruminants. IMPORTANCEEnterohemorrhagic Escherichia coli (EHEC) are foodborne pathogenic bacteria causing intestinal infection that may lead to hemorrhagic colitis and hemolytic uremic syndrome (HUS) particularly in young children. There is no effective treatment, and antibiotics are contraindicated because they promote the development of HUS. Vaccination of ruminants, the main reservoir of EHEC, has been proposed as an important strategy to reduce the fecal shedding of EHEC to reduce transmission to humans. Outer Membrane Vesicles (OMVs) derived from E. coli are a highly attractive vaccine platform. Here, we produced OMVs enriched with the C-terminal part of the intimin (Int280). As a proof of concept, we used a mice model of Citrobacter rodentium colonization as a surrogate for EHEC intestinal colonization. Vaccination elicited antibodies against intimin and decreased the duration of fecal shedding of C. rodentium. Therefore, this OMV-Int280 vaccine is a promising candidate to control EHEC intestinal carriage and fecal shedding in ruminants.

microbiology↗

bioRxiv2021

Insights into the acquisition of the pks island and production of colibactin in the Escherichia coli population

The pks island codes for the enzymes necessary for synthesis of the genotoxin colibactin, which contributes to the virulence of Escherichia coli strains and is suspected of promoting colorectal cancer. From a collection of 785 human and bovine E. coli isolates, we identified 109 strains carrying a highly conserved pks island, mostly from the phylogroup B2, but also from phylogroups A, B1 and D. Different scenarios of pks acquisition were deduced from whole genome sequence and phylogenetic analysis. In the main scenario, pks was introduced and stabilized into certain sequence types (ST) of the B2 phylogroup, such as ST73 and ST95, at the asnW tRNA locus located in the vicinity of the yersiniabactin-encoding High Pathogenicity Island (HPI). In a few B2 strains, pks inserted at the asnU or asnV tRNA loci close to the HPI and occasionally was located next to the remnant of an integrative and conjugative element. In a last scenario specific to B1/A strains, pks was acquired, independently of the HPI, at a non-tRNA locus. All the pks-positive strains except 18 produced colibactin. Sixteen strains contained mutations in clbB or clbD, or a fusion of clbJ and clbK and were no longer genotoxic but most of them still produced low amount of potentially active metabolites associated with the pks island. One strain was fully metabolically inactive without pks alteration, but colibactin production was restored by overexpressing the ClbR regulator. In conclusion, the pks island is not restricted to human pathogenic B2 strains and is more widely distributed in the E. coli population, while preserving its functionality. IMPACT STATEMENTColibactin, a genotoxin associated with the carcinogenicity of certain strains of E. coli, is encoded by a pathogenicity island called pks. We took advantage of a large collection of non-clinical E. coli strains originating from human and bovine hosts to explore the distribution, conservation and functionality of the pks island. We found that the pks island was not only present in the phylogroup B2 (and more specifically to certain B2 sublineages), but also in other genetic phylogroups, highlighting its capacity to disseminate though horizontal gene transfer. We identified various genetic pks configurations indicative of an introduction of the pks island into E. coli on multiple independent occasions. Despite the existence of various acquisition scenarios, we found that the pks sequences were highly conserved and pks-carrying strains were overwhelmingly capable of producing colibactin, suggesting that the pks island is under selective pressure, through the production of colibactin or other secondary metabolites. Future implications include the identification of such metabolites and their biological activities that could be advantageous to E. coli and enable its adaptation to various ecological niches. DATA SUMMARYAll sequence data of the 785 E. coli used in this study are freely available from the NCBI BioProject database (https://www.ncbi.nlm.nih.gov/bioproject/) under the accession number PRJDB5579. This database was updated to include the sequence data obtained using ONT MinION for the E. coli reference strain SP15 and for E. coli strains ECSC054, JML285, KS-NP019, NS-NP030 and SI-NP020. The sequence data of E. coli strain UPEC129 obtained using PacBio instrument were deposited in the NCBI BioProject database and are available at https://www.ncbi.nlm.nih.gov/Traces/study/ under the accession number PRJNA669570. Hybrid MinION-Illumina and PacBio-Illumina assemblies are available at the NCBI nucleotide database. The genome sequences of 36 other E. coli reference strains and 7 non-E. coli strains were retrieved from NCBI.

microbiology↗