Genotoxic Escherichia coli Strains Encoding Colibactin, Cytolethal Distending Toxin, and Cytotoxic Necrotizing Factor in Laboratory Rats

Abstract

Escherichia coli is a gram-negative bacillus that colonizes the gastrointestinal tract of humans and animals. 46 Although some strains are considered commensals, various intestinal and extraintestinal pathogenic E. coli pathotypes are associated with a wide range of clinical disease states in the host; 16,41 these strains are responsible for the deaths of more than 2 million humans annually. 65 Specific pathotypes often harbor similar virulence factors and correspond to distinct clinical and histologic lesions. Intestinal pathotypes include enteropathogenic E. coli, enterohemorrhagic E. coli, enteroinvasive E. coli, enterotoxigenic E. coli, enteroaggregative E. coli, diffusely adhering E. coli, and adherent-invasive E. coli. 65 Extraintestinal pathotypes include uropathogenic E. coli and neonatal meningitis E. coli, both of which have an enhanced ability to translocate through the intestinal epithelium and cause severe clinical disease.E. coli strains typically are classified into 1 of the 4 major phylogenetic groups: A, B1, B2, and D. 10,14,60 Groups B2 and D are often associated with pathogenicity, whereas fecal strains belonging to groups A and B1 generally lack virulence factors. 22,60 Strains belonging to pathogroup B2 have been isolated from the feces of persons from developed countries with increasing frequency. 52,70 These pathogenic strains encode various combinations of virulence genes and pathogenicity islands which promote invasion and colonization, evasion of host defenses, and damage to host tissues. Associated virulence factors include cytotoxins such as genotoxic cyclomodulins, cytotoxic necrotizing factors (cnf), cytolethal distending toxin (cdt), and the genotoxin colibactin (pks). These virulence factors modulate host cellular differentiation, proliferation, and apoptosis and promote cytopathic effects. 7,21,69 CNF is a 115-kDa cyclomodulin protein that induces cell-cycle alterations and cytoskeletal changes by activating rho GTPases, which leads to a variety of aberrant phenotypic effects including micropinocytosis, megalocytosis, and multinucleation. 62 cnf1 is chromosomally encoded, 23 whereas cnf2 is plasmid-encoded. 20 cnf-producing E. coli are considered necrotoxigenic and are associated with intestinal, urinary, 23 and meningeal infection of humans. 41 cnf + E. coli have previously been isolated from clinically

Cytotoxic Escherichia coli strains encoding colibactin, cytotoxic necrotizing factor, and cytolethal distending toxin colonize laboratory common marmosets (Callithrix jacchus)

“…Cells treated with cyclomodulin-negative E. coli strains were indistinguishable from those treated with nonpathogenic K12 strain. These results were consistent with findings from previous studies showing cytotoxic effects of pks+, cnf+ and cdt+ E. coli in vitro 11,26,28,29,33 .…”

“…Pathogenic E. coli strains typically belong to phylogroups B2 or D, whereas those in phylogroups A and B1 are usually considered commensals 37 . Ninetyeight percent of the cyclomodulin-encoding E. coli isolated from laboratory marmosets belong to phylogenetic group B2, which is consistent with strains isolated from humans and other species 11,[26][27][28]33,38 . The distribution of phylogroups was significantly different in Colony B, which had 61% prevalence of the non-pathogenic phylogroup A, whereas the prevalence of phylogroup A in Colony A was only 3%, and it was not isolated in Colony Table 2.…”

“…Syntenic alignments were confirmed for the pks island in all four predicted marmoset E. coli isolates with E. coli strains IHE3034 and NC101. (Supplementary Figure S5) Isolate S4 was found to have a putative hybrid gene for clbJ-K, similar to a gene sequence found previously in E. coli isolates from laboratory and pet rats 28,33 . Gene sequences homologous to the hlyCABD-cnf1 operon present in UTI89 were detected in marmoset E. coli isolates S1 and S3, as predicted by the results of PCR and in vitro cytotoxicity assays.…”

“…Interestingly, 96% of the cnf + isolates from marmosets did not demonstrate hemolysis due to an insertion event in the hlyA gene. Strains of E. coli with a similar deactivating insertion in the hlyA gene were previously isolated from laboratory rats from a specific vendor 28 .…”

Colon Carcinogenesis: The Interplay Between Diet and Gut Microbiota

“…Interestingly, the production of genotoxin is not restricted to only the typically pathogenic bacteria but also commensal bacteria. E. coli constitutes a normal component of the gut microbiome, but certain strains that acquire pathogen-like features can produce cyclomodulin genotoxin including colibactin, cytotoxic necrotizing factor (CNF), and cytolethal distending toxin (CDT) ( Kurnick et al., 2019 ), all of which have been examined for their promoting effect in CRC. The pathogenicity island encoding colibactin, known as polyketide synthase (pks), are detected in up to 66.7% of CRC patients ( Arthur et al., 2012 ).…”