ClbG in Avian Pathogenic Escherichia coli Contributes to Meningitis Development in a Mouse Model

The Diversity of Escherichia coli Pathotypes and Vaccination Strategies against This Versatile Bacterial Pathogen

Escherichia coli (E. coli) is a gram-negative bacillus and resident of the normal intestinal microbiota. However, some E. coli strains can cause diseases in humans, other mammals and birds ranging from intestinal infections, for example, diarrhea and dysentery, to extraintestinal infections, such as urinary tract infections, respiratory tract infections, meningitis, and sepsis. In terms of morbidity and mortality, pathogenic E. coli has a great impact on public health, with an economic cost of several billion dollars annually worldwide. Antibiotics are not usually used as first-line treatment for diarrheal illness caused by E. coli and in the case of bloody diarrhea, antibiotics are avoided due to the increased risk of hemolytic uremic syndrome. On the other hand, extraintestinal infections are treated with various antibiotics depending on the site of infection and susceptibility testing. Several alarming papers concerning the rising antibiotic resistance rates in E. coli strains have been published. The silent pandemic of multidrug-resistant bacteria including pathogenic E. coli that have become more difficult to treat favored prophylactic approaches such as E. coli vaccines. This review provides an overview of the pathogenesis of different pathotypes of E. coli, the virulence factors involved and updates on the major aspects of vaccine development against different E. coli pathotypes.

RyhB in Avian Pathogenic Escherichia coli Regulates the Expression of Virulence-Related Genes and Contributes to Meningitis Development in a Mouse Model

Avian pathogenic Escherichia coli (APEC) is an important member of extraintestinal pathogenic Escherichia coli (ExPEC). It shares similar pathogenic strategies with neonatal meningitis E. coli (NMEC) and may threaten human health due to its potential zoonosis. RyhB is a small non-coding RNA that regulates iron homeostasis in E. coli. However, it is unclear whether RyhB regulates meningitis occurrence. To investigate the function of RyhB in the development of meningitis, we constructed the deletion mutant APEC XM∆ryhB and the complemented mutant APEC XM∆ryhB/pryhB, established a mouse meningitis model and evaluated the role of RyhB in virulence of APEC. The results showed that the deletion of ryhB decreased biofilm formation, adhesion to the brain microvascular endothelial cell line bEnd.3 and serum resistance. RNA-seq data showed that the expression of multiple virulence-related genes changed in the ryhB deletion mutant in the presence of duck serum. Deletion of ryhB reduced the clinical symptoms of mice, such as opisthotonus, diarrhea and neurological signs, when challenged with APEC. Compared with the mice infected with the wild-type APEC, fewer histopathological lesions were observed in the brain of mice infected with the ryhB deletion mutant APEC XM∆ryhB. The bacterial loads in the tissues and the relative expression of cytokines (IL-1β, IL-6, and TNF-α) in the brain significantly decreased when challenged with the APEC XM∆ryhB. The expressions of tight junction proteins (claudin-5, occludin and ZO-1) were not reduced in the brain of mice infected with APEC XM∆ryhB; that is, the blood-brain barrier permeability of mice was not significantly damaged. In conclusion, RyhB contributes to the pathogenicity of APEC XM in the meningitis-causing process by promoting biofilm formation, adhesion to endothelial cells, serum resistance and virulence-related genes expression.

Phosphopantetheinyl transferase ClbA contributes to the virulence of avian pathogenic Escherichia coli in meningitis infection of mice

Avian pathogenic Escherichia coli (APEC), which has potential zoonotic risk, can cause severe systemic infections such as septicemia and meningitis in poultry. Colibactin is a hybrid non-ribosomal peptide/polyketide secondary metabolite produced by bacteria, which induces double-strand DNA breaks and chromosome instability in eukaryotic cells. ClbA is a 4’-phosphopantetheinyl transferase (PPTase) that is essential for colibactin and plays a role in siderophore synthesis. However, whether ClbA is associated with meningitis development in APEC is unclear. In this study, we abolished the clbA gene in the APEC XM strain, investigated the effect of clbA on colibactin synthesis and evaluated the pathogenic capacity of colibactin on meningitis development. Deletion of clbA reduced DNA damage to cells and hindered the normal synthesis of colibactin. Compared with the mice infected by wild-type APEC XM, the clbA deletion mutant infected mice had significant reduction in a series of characteristics associated with meningitis including clinical symptoms, bacterial loads of blood and brain, disruption of the blood brain barrier and the expression of inflammatory factors in the brain tissue. Complementation of ClbA recovered some APEC XM virulence. We conclude that ClbA is obligatory for the synthesis of colibactin and is responsible for the development of meningitis in mice infected by APEC.

Tackling the Threat of Cancer Due to Pathobionts Producing Colibactin: Is Mesalamine the Magic Bullet?

Colibactin is a genotoxin produced primarily by Escherichia coli harboring the genomic pks island (pks⁺ E. coli). Pks⁺ E. coli cause host cell DNA damage, leading to chromosomal instability and gene mutations. The signature of colibactin-induced mutations has been described and found in human colorectal cancer (CRC) genomes. An inflamed intestinal environment drives the expansion of pks⁺ E. coli and promotes tumorigenesis. Mesalamine (i.e., 5-aminosalycilic acid), an effective anti-inflammatory drug, is an inhibitor of the bacterial polyphosphate kinase (PPK). This drug not only inhibits the production of intestinal inflammatory mediators and the proliferation of CRC cells, but also limits the abundance of E. coli in the gut microbiota and diminishes the production of colibactin. Here, we describe the link between intestinal inflammation and colorectal cancer induced by pks⁺ E. coli. We discuss the potential mechanisms of the pleiotropic role of mesalamine in treating both inflammatory bowel diseases and reducing the risk of CRC due to pks⁺ E. coli.