The Escherichia coli Hemolysin

Dual role of CsrA in regulating the hemolytic activity of Escherichia coli O157:H7

Post-transcriptional global carbon storage regulator A (CsrA) is a sequence-specific RNA-binding protein involved in the regulation of multiple bacterial processes. Hemolysin is an important virulence factor in the enterohemorrhagic Escherichia coli O157:H7 (EHEC). Here, we show that CsrA plays a dual role in the regulation of hemolysis in EHEC. CsrA significantly represses plasmid-borne enterohemolysin (EhxA)-mediated hemolysis and activates chromosome-borne hemolysin E (HlyE)-mediated hemolysis through different mechanisms. RNA structure prediction revealed a well-matched stem-loop structure with two potential CsrA binding sites located on the 5' untranslated region (UTR) of ehxB, which encodes a translocator required for EhxA secretion. CsrA inhibits EhxA secretion by directly binding to the RNA leader sequence of ehxB to repress its expression in two different ways: CsrA either binds to the Shine–Dalgarno sequence of ehxB to block ribosome access or to ehxB transcript to promote its mRNA decay. The predicted CsrA-binding site 1 of ehxB is essential for its regulation. There is a single potential CsrA-binding site at the 5'-end of the hlyE transcript, and its mutation completely abolishes CsrA-dependent activation. CsrA can also stabilize hlyE mRNA by directly binding to its 5' UTR. Overall, our results indicate that CsrA acts as a hemolysis modulator to regulate pathogenicity under certain conditions.

Vaccination against Bacterial Infections: Challenges, Progress, and New Approaches with a Focus on Intracellular Bacteria

Many bacterial infections are major health problems worldwide, and treatment of many of these infectious diseases is becoming increasingly difficult due to the development of antibiotic resistance, which is a major threat. Prophylactic vaccines against these bacterial pathogens are urgently needed. This is also true for bacterial infections that are still neglected, even though they affect a large part of the world's population, especially under poor hygienic conditions. One example is typhus, a life-threatening disease also known as "war plague" caused by Rickettsia prowazekii, which could potentially come back in a war situation such as the one in Ukraine. However, vaccination against bacterial infections is a challenge. In general, bacteria are much more complex organisms than viruses and as such are more difficult targets. Unlike comparatively simple viruses, bacteria possess a variety of antigens whose immunogenic potential is often unknown, and it is unclear which antigen can elicit a protective and long-lasting immune response. Several vaccines against extracellular bacteria have been developed in the past and are still used successfully today, e.g., vaccines against tetanus, pertussis, and diphtheria. However, while induction of antibody production is usually sufficient for protection against extracellular bacteria, vaccination against intracellular bacteria is much more difficult because effective defense against these pathogens requires T cell-mediated responses, particularly the activation of cytotoxic CD8+ T cells. These responses are usually not efficiently elicited by immunization with non-living whole cell antigens or subunit vaccines, so that other antigen delivery strategies are required. This review provides an overview of existing antibacterial vaccines and novel approaches to vaccination with a focus on immunization against intracellular bacteria.

Meningitic Escherichia coli α-hemolysin aggravates blood-brain barrier disruption via targeting TGFβ1-triggered hedgehog signaling

Bacterial meningitis is a life-threatening infectious disease with severe neurological sequelae and a high mortality rate, in which Escherichia coli is one of the primary Gram-negative etiological bacteria. Meningitic E. coli infection is often accompanied by an elevated blood–brain barrier (BBB) permeability. BBB is the structural and functional barrier composed of brain microvascular endothelial cells (BMECs), astrocytes, and pericytes, and we have previously shown that astrocytes-derived TGFβ1 physiologically maintained the BBB permeability by triggering a non-canonical hedgehog signaling in brain microvascular endothelial cells (BMECs). Here, we subsequently demonstrated that meningitic E. coli infection could subvert this intercellular communication within BBB by attenuating TGFBRII/Gli2-mediated such signaling. By high-throughput screening, we identified E. coli α-hemolysin as the critical determinant responsible for this attenuation through Sp1-dependent TGFBRII reduction and triggering Ca²⁺ influx and protein kinase A activation, thus leading to Gli2 suppression. Additionally, the exogenous hedgehog agonist SAG exhibited promising protection against the infection-caused BBB dysfunction. Our work revealed a hedgehog-targeted pathogenic mechanism during meningitic E. coli-caused BBB disruption and suggested that activating hedgehog signaling within BBB could be a potential protective strategy for future therapy of bacterial meningitis.

Poultry-origin extraintestinal Escherichia coli strains carrying the traits associated with urinary tract infection, sepsis, meningitis and avian colibacillosis in India

AIM

In-depth 'One Health' risk assessment of extraintestinal pathogenic Escherichia coli (ExPEC) strains carrying the traits of urinary tract infection, sepsis, meningitis and avian colibacillosis in poultry of India.

METHODS AND RESULTS

A total of 230 E. coli isolates were recovered from chicken samples representing the different sources (faeces vs caeca), stages (poultry farms vs retails butcher shop) or environments (rural vs urban) of poultry in India. Among all poultry-origin E. coli isolates, 49 (21·1%) strains were identified as ExPEC possessing multiple virulence determinants regardless of their association with any specific phylogenetic lineages. Of particular, potentially virulent ExPEC pathotypes, that is, uropathogenic E.coli (UPEC, 20·4%), avian pathogenic E. coli (APEC, 34·6%), septicaemia-associated E. coli (SEPEC, 47·0%) and neonatal meningitis-causing E.39 coli (NMEC, 2·0%) were also detected among all ExPEC strains.

CONCLUSIONS

Our study is the first to assess ExPEC strains circulating in the different settings of poultry in India and significantly demonstrates their potential ability to cause multiple extraintestinal infections both in humans and animals.

SIGNIFICANCE AND IMPACT OF THE STUDY

The data of our study are in favour of the possibility that poultry-origin putative virulent ExPEC pathotypes consequently constitute a threat risk to 'One Health' or for food safety and a great concern for poultry production of India.