The YfcO fimbriae gene enhances adherence and colonization abilities of avian pathogenic Escherichia coli in vivo and in vitro

Avian pathogenic Escherichia coli: Epidemiology, virulence and pathogenesis, diagnosis, pathophysiology, transmission, vaccination, and control

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in poultry; this type of bacteria is an extraintestinal pathogen E. coli. Unlike other E. coli pathogen groups, the characteristics of APECs cannot be identified by a single group. Serotyping and biotyping are frequently performed for isolates found in colibacillosis infections. The establishment, transmission, and persistence of this pathogenic strain in chicken populations are determined by the intricate interactions of multiple elements that make up the epidemiology of APEC. APEC employs many virulence and pathogenesis factors or mechanisms to infect chickens with colibacillosis. These factors include invasives, protectins, adhesins, iron acquisition, and toxins. In addition, the pathogenicity of APEC strains can be evaluated in 2-4 week-old chicks. The impact of unfavorable environmental conditions has also been documented, despite direct contact being demonstrated to be a significant element in transmission in APEC. Chickens are immunized against colibacillosis using a variety of vaccines. Nevertheless, commercially available vaccinations do not offer sufficient immunity to protect birds from APEC strains. Hatching egg contamination is one of the main ways that APECs spread throughout chicken flocks. Farmers also need to be mindful of storing discarded materials near the manure-watering area, removing them when necessary, and replacing wet materials with dry materials when needed. This review aimed to explain the characteristics, epidemiology, virulence, pathogenesis, diagnosis, pathophysiology, transmission, vaccination, and control of APEC.

Orf1B controls secretion of T3SS proteins and contributes to Edwardsiella piscicida adhesion to epithelial cells

Edwardsiella piscicida is a Gram-negative enteric pathogen that causes hemorrhagic septicemia in fish. The type III secretion system (T3SS) is one of its two most important virulence islands. T3SS protein EseJ inhibits E. piscicida adhesion to epithelioma papillosum cyprini (EPC) cells by negatively regulating type 1 fimbria. Type 1 fimbria helps E. piscicida to adhere to fish epithelial cells. In this study, we characterized a functional unknown protein (Orf1B) encoded within the T3SS gene cluster of E. piscicida. This protein consists of 122 amino acids, sharing structural similarity with YscO in Vibrio parahaemolyticus. Orf1B controls secretion of T3SS translocon and effectors in E. piscicida. By immunoprecipitation, Orf1B was shown to interact with T3SS ATPase EsaN. This interaction may contribute to the assembly of the ATPase complex, which energizes the secretion of T3SS proteins. Moreover, disruption of Orf1B dramatically decreased E. piscicida adhesion to EPC cells due to the increased steady-state protein level of EseJ within E. piscicida. Taken together, this study partially unraveled the mechanisms through which Orf1B promotes secretion of T3SS proteins and contributes to E. piscicida adhesion. This study helps to improve our understanding on molecular mechanism of E. piscicida pathogenesis.

Development of a hyper-adhesive and attenuated Edwardsiella ictaluri strain as a novel immersion vaccine candidate in yellow catfish (Pelteobagrus fulvidraco)

Edwardsiella ictaluri, a Gram-negative intracellular pathogen, is the causative agent of enteric septicemia in channel catfish, and catfish aquaculture in China suffers heavy economic losses due to E. ictaluri infection. Vaccination is an effective control measure for this disease. In this study, an attenuated E. ictaluri strain was acquired through deletion mutation of the T3SS protein eseJ_ei, and the ΔeseJ_ei strain fails to replicate in the epithelioma papillosum of carp cells. The type 1 fimbria plays a pivotal role in the adhesion of E. ictaluri, and it was found in this study that deletion of -245 to -50 nt upstream of fimA increases its adhesion to around five times that of the WT strain. A hyper-adhesive and highly attenuated double mutant (ΔeseJ_eiΔfimA_-245-_-50 strain) was constructed, and it was used as a vaccine candidate in yellow catfish via bath immersion at a dosage of 1 × 10⁵ CFU/mL. It was found that this vaccine candidate can stimulate protection when challenged with E. ictaluri HSN-1 at 5 × 10⁷ CFU/mL (∼20 × LD₅₀). The survival rate was 83.61% for the vaccinated group and 33.33% for the sham-vaccinated group. The RPS (relative percent of survival) of the vaccination trial reached 75.41%. In conclusion, the ΔeseJ_eiΔfimA_-245-_-50 strain developed in this study can be used as a vaccine candidate. It excels in terms of ease of delivery (via bath immersion) and is highly efficient in stimulating protection against E. ictaluri infection.

The Transcription Regulator YgeK Affects Biofilm Formation and Environmental Stress Resistance in Avian Pathogenic Escherichia coli

Simple Summary

Avian pathogenic Escherichia coli (APEC) is the pathogen responsible for colibacillosis in poultry. Transcriptional regulator ygeK has been shown to decrease APEC’s flagellar formation ability, bacterial motility ability, serum sensitivity, and adhesion ability. However, we did not study the effects of ygeK on biofilm formation and environmental stress resistance in APEC. In this study, we investigated ygeK in APEC biofilm formation and bacterial resistance to different environmental stresses. We also analyzed the multi-level regulation of ygeK in APEC and investigated associations between differentially expressed proteins and key ygeK targets. This work provides a basis for further analysis of APEC pathogenesis mechanisms.

Abstract

Avian pathogenic Escherichia coli (APEC) is one of the most common pathogens in poultry and a potential gene source of human extraintestinal pathogenic E. coli (ExPEC), leading to serious economic losses in the poultry industry and public health concerns. Exploring the pathogenic mechanisms underpinning APEC and the identification of new targets for disease prevention and treatment are warranted. YgeK is a transcriptional regulator in APEC and is localized to the type III secretion system 2 of E. coli. In our previous work, the transcription factor ygeK significantly affected APEC flagella formation, bacterial motility, serum sensitivity, adhesion, and virulence. To further explore ygeK functions, we evaluated its influence on APEC biofilm formation and resistance to environmental stress. Our results showed that ygeK inactivation decreased biofilm formation and reduced bacterial resistance to environmental stresses, including acid and oxidative stress. In addition, the multi-level regulation of ygeK in APEC was analyzed using proteomics, and associations between differentially expressed proteins and the key targets of ygeK were investigated. Overall, we identified ygeK’s new function in APEC. These have led us to better understand the transcriptional regulatory ygeK and provide new clues about the pathogenicity of APEC.

Avian Pathogenic Escherichia coli (APEC): An Overview of Virulence and Pathogenesis Factors, Zoonotic Potential, and Control Strategies

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in avian species, and recent reports have suggested APEC as a potential foodborne zoonotic pathogen. Herein, we discuss the virulence and pathogenesis factors of APEC, review the zoonotic potential, provide the current status of antibiotic resistance and progress in vaccine development, and summarize the alternative control measures being investigated. In addition to the known virulence factors, several other factors including quorum sensing system, secretion systems, two-component systems, transcriptional regulators, and genes associated with metabolism also contribute to APEC pathogenesis. The clear understanding of these factors will help in developing new effective treatments. The APEC isolates (particularly belonging to ST95 and ST131 or O1, O2, and O18) have genetic similarities and commonalities in virulence genes with human uropathogenic E. coli (UPEC) and neonatal meningitis E. coli (NMEC) and abilities to cause urinary tract infections and meningitis in humans. Therefore, the zoonotic potential of APEC cannot be undervalued. APEC resistance to almost all classes of antibiotics, including carbapenems, has been already reported. There is a need for an effective APEC vaccine that can provide protection against diverse APEC serotypes. Alternative therapies, especially the virulence inhibitors, can provide a novel solution with less likelihood of developing resistance.

The Edwardsiella piscicida Type III Effector EseJ Suppresses Expression of Type 1 Fimbriae, Leading to Decreased Bacterial Adherence to Host Cells

The type III secretion system (T3SS) of Edwardsiella piscicida plays a crucial role in its pathogenesis. Our previous study indicated that the T3SS effector protein EseJ inhibits the bacterium's adhesion to epithelioma papillosum cyprini (EPC) cells, while the mechanism of the inhibition remains elusive. In this study, we revealed that EseJ negatively regulates the fimA gene, as demonstrated by comparative transcription analysis of ΔeseJ and wild-type (WT) strains. As well, the dramatically increased production of FimA was detected in the absence of EseJ compared to that by the WT strain. The adherence of the ΔeseJ strain decreased far below that of the WT strain in the absence of FimA, demonstrating that FimA plays a pivotal role in the hyperadhesion of the ΔeseJ strain. Adherence analysis with a strain with truncated eseJ demonstrated that the C-terminal region of EseJ (Gly1191 to Ile1359) is necessary to inhibit the transcription of the type 1 fimbrial operon. Binding between the EseJ fragment from amino acid residues 1191 to 1359 and the DNA fragment upstream of fimA was not detected, indicating that EseJ might indirectly regulate the type 1 fimbrial operon. Our study reveals that EseJ controls E. piscicida adherence to EPC cells by negatively regulating the type 1 fimbrial operon.

Prophage phiv142-3 enhances the colonization and resistance to environmental stresses of avian pathogenic Escherichia coli

Bacterial acquisition of prophages reflects natural selection. Phage DNA has been shown to constitute up to 20% if bacterial genomes. However, prophages' role in Avian Pathogenic Escherichia coli (APEC) is unclear. In this study, APEC strain DE142 harboring prophage phiv142-3, was subjected to deletion and the WT and deletion mutant were characterized under a range of conditions. Prophage deletion mutant DE142Δphiv142-3 was constructed and characterized. The DE142Δphiv142-3 colonies were much smaller than those of the wild-type, and the mutant cells were elongated. The mutant showed reduced adherence to DF-1 cells (87.4% reduction) compared to the wild-type (P < 0.001), and showed a significantly decreased resistance to the killing action of serum (P < 0.001). The mutant demonstrated 95.6%, 71.6%, and 99.6% reduced survival under acid, alkaline, and oxidative stress, respectively. In vitro competition assays showed that the cell number of the mutant was about one-tenth that of the wild-type (competitive index (CI) value, 0.1177). In vivo, the mutant showed significantly decreased colonization of chicken tissues compared with the wild-type. Thus phiv142-3 helps DE142 cope with adverse environments and aids bacterial colonization.