EntE, EntS and TolC synergistically contributed to the pathogenesis of APEC strain E058

Whole-genome analysis of five Escherichia coli strains isolated from focal duodenal necrosis in laying hens reveals genetic similarities to the E. coli O25:H4 ST131 strain

Focal duodenal necrosis (FDN) is an intestinal disease causing significant economic losses in the table-egg industry due to reduced egg production in laying hens. Its etiology and pathogenesis remain poorly understood. Between 2021 and 2023, 111 Escherichia coli isolates were collected from FDN lesions and screened for the presence of virulence genes using PCR panels. Five strains-FDN-4, FDN-9, FDN-11, FDN-24, and FDN-50-were selected for whole-genome sequencing due to their high virulence gene content. Core-genome analyses found that the five FDN E. coli belong to different phylogroups and strain types (ST), but they all share multiple complete operons involved in key pathogenic functions, including host cell adhesion and invasion, iron acquisition, motility, biofilm formation, and acid resistance. Comparative genomic analyses identified FDN-4 as the most genetically distinct strain, closely resembling EC958, an O25b:H4 ST131 uropathogenic E. coli (UPEC) commonly associated with extended-spectrum beta-lactamase production. FDN-4 and EC958 share unique chromosomal virulence genes absent in the other FDN strains, all located within genomic islands. This study provides the first complete genomic characterization of E. coli isolated from FDN lesions and highlights FDN-4 as a genetically distinct strain with similarities to O25b:H4 ST131 UPEC.IMPORTANCEThis study presents the first complete genomic characterization of Escherichia coli isolated from focal duodenal necrosis (FDN) lesions. Notably, FDN-4 is the first E. coli strain from a poultry disease (FDN) to show significant similarity to O25b:H4 ST131 strains, commonly classified as uropathogenic E. coli and often associated with extended-spectrum beta-lactamase production. However, caution is warranted when attributing direct transmission routes between poultry and humans.

Avian pathogenic Escherichia coli (APEC): current insights and future challenges

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in avian species, and new investigations have implicated APEC as a possible foodborne zoonotic pathogen. This review analyzes APEC's pathogenic and virulence features, assesses the zoonotic potential, provides an update on antibiotic resistance and vaccine research efforts, and outlines alternate management approaches. Aside from established virulence factors, various additional components, including 2-component systems (TCS), adhesins, secretion systems (SS), invasions, iron acquisition systems, quorum sensing systems (QS), transcriptional regulators (TR), toxins, and genes linked with metabolism, contribute to APEC pathogenesis. APEC may spread to diverse species of birds in all business sectors and can infect birds of varying ages. However, younger birds experience more severe sickness than mature ones, probably due to their developing immune systems, and stress factors such as vaccination, Mycoplasma Infections, poor housing circumstances, respiratory viruses, and other risk factors for secondary infections can all make APEC both primary and secondary pathogens. Understanding these factors will help in generating new and effective treatments. Moreover, APEC O145 was the most prevalent serotype recently reported in all of China. Thus, the APEC's zoonotic potential should not be underrated. Furthermore, it has already been noted that APEC is resistant to almost all antibiotic classes, including carbapenems. A robust vaccine capable of protecting against multiple APEC serotypes is urgently needed. Alternative medications, particularly virulence inhibitors, can provide a special method with a decreased likelihood of acquiring resistance.

Genome-wide identification of genes critical for in vivo fitness of multi-drug resistant porcine extraintestinal pathogenic Escherichia coli by transposon-directed insertion site sequencing using a mouse infection model

Extraintestinal pathogenic Escherichia coli (ExPEC) is an important zoonotic pathogen. Recently, ExPEC has been reported to be an emerging problem in pig farming. However, the mechanism of pathogenicity of porcine ExPEC remains to be revealed. In this study, we constructed a transposon (Tn) mutagenesis library covering Tn insertion in over 72% of the chromosome-encoded genes of a virulent and multi-drug resistant porcine ExPEC strain PCN033. By using a mouse infection model, a transposon-directed insertion site sequencing (TraDIS) assay was performed to identify in vivo fitness factors. By comparing the Tn insertion frequencies between the input Tn library and the recovered library from different organs, 64 genes were identified to be involved in fitness during systemic infection. 15 genes were selected and individual gene deletion mutants were constructed. The in vivo fitness was evaluated by using a competitive infection assay. Among them, ΔfimG was significantly outcompeted by the WT strain in vivo and showed defective adhesion to host cells. rfa which was involved in lipopolysaccharide biosynthesis was shown to be critical for in vivo fitness which may have resulted from its role in the resistance to serum killing. In addition, several metabolic genes including fepB, sdhC, fepG, gltS, dcuA, ccmH, ddpD, narU, glpD, malM, and yabL and two regulatory genes metJ and baeS were shown as important determinants of in vivo fitness of porcine ExPEC. Collectively, this study performed a genome-wide screening for in vivo fitness factors which will be important for understanding the pathogenicity of porcine ExPEC.

Effects of TolC on the pathogenicity of porcine extraintestinal pathogenic Escherichia coli

Extraintestinal pathogenic Escherichia coli (ExPEC) is a well-known critical pathogenic zoonosis that causes extraintestinal infections in humans and animals by affecting their immune organs. Recently, research on the outer membrane protein of E. coli, tolerant colicin (TolC), a virulent protein in the formation of the ExPEC efflux pump, has been an attractive subject. However, the pathogenic mechanisms remain unclear. This study aimed to explore the role of TolC in the pathogenesis of the ExPEC strain PPECC42; a complementation strain (Cm-TolC) and an isogenic mutant (ΔTolC) were constructed. Loss of TolC drastically impaired the virulence of ExPEC in an experimental mouse model. ΔTolC showed a substantial decrease in the porcine aortic vascular endothelial cell (PAVEC) adherence, invasion, and pro-inflammatory response, in contrast to that of the wild type, with a reduced survival ratio in both the bacterial load and whole blood in mice. ΔTolC also showed decreased expression of necroptosis signals such as receptor-interacting protein kinase 1, phosphorylated mixed-lineage kinase domain-like protein, and mitochondrial proteins such as phosphoglycerate mutase family member 5. Our data suggest that TolC is closely associated with ExPEC pathogenesis. These results provide scientific grounds for exploring the potential of TolC as an effective drug target for controlling ExPEC infection, screening new inhibitors, and developing new drugs. This will allow for further prevention and control of ExPEC infection.

The novel LysR-family transcriptional regulator BvtR is involved in the resistance of Brucella abortus to nitrosative stress, detergents and virulence through the genetic regulation of diverse pathways

Brucella is a facultative intracellular bacterium lacking classical virulence factors; its virulence instead depends on its ability to invade and proliferate within host cells. After entering cells, Brucella rapidly modulates the expression of a series of genes involved in metabolism and immune evasion. Here, a novel LysR-family transcriptional regulator, designated Brucellavirulence-related transcriptional regulator (BvtR), was found to be associated with Brucella abortus virulence. We first successfully constructed a BvtR mutant, ΔbvtR, and a complemented strain, ΔbvtR-Com. Subsequently, we performed cell infection experiments, which indicated that the ΔbvtR strain exhibited similar adhesion, invasion and survival within HeLa cells or RAW264.7 macrophages to those of the wild-type strain. In stress resistance tests, the ΔbvtR strain showed enhanced sensitivity to sodium nitroprusside and sodium dodecyl sulfate, but not to hydrogen peroxide, cumene hydroperoxide, polymyxin B and natural serum. Mouse infection experiments indicated that the virulence of the ΔbvtR strain significantly decreased at 4 weeks post-infection. Finally, we analyzed differentially expressed genes regulated by BvtR with RNA-seq, COG classification and KEGG pathway analysis. Nitrogen metabolism, siderophore biosynthesis and oligopeptide transport were found to be the predominantly altered functions, and key metabolic and regulatory networks were delineated in the ΔbvtR mutant. Thus, we identified a novel Brucella virulence-related regulator, BvtR, and demonstrated that BvtR regulation affects Brucella resistance to killing by sodium nitroprusside and sodium dodecyl sulfate. The differentially expressed genes responding to BvtR are involved in diverse functions or pathways in Brucella, thus, suggesting the breadth of BvtR's regulatory functions. This study provides novel clues regarding Brucella pathogenesis.

Vibrio cholerae TolC is required for expression of the ToxR regulon

Vibrio cholerae is a Gram-negative bacterium that causes the enteric disease cholera. V. cholerae colonization of the human intestine is dependent on the expression of both virulence genes and environmental adaptation genes involved in antimicrobial resistance. The expression of virulence genes, including the genes encoding for the main virulence factors cholera toxin (CT) and the toxin coregulated pilus (TCP), are coordinately regulated by the ToxR regulon. Tripartite transport systems belonging to the ATP binding cassette, major facilitator, and Resistance-Nodulation-Division families are critical for V. cholerae pathogenesis. Transport systems belonging to these families contribute to myriad phenotypes including protein secretion, antimicrobial resistance and virulence. TolC plays a central role in bacterial physiology by functioning as the outer membrane pore protein for tripartite transport systems. Consistent with this, V. cholerae tolC was previously found to be required for MARTX toxin secretion and antimicrobial resistance. Herein we investigated the contribution of TolC to V. cholerae virulence. We documented that tolC was required for CT and TCP production in O1 El Tor V. cholerae. This phenotype was linked to repression of the critical ToxR regulon transcription factor aphA. Decreased aphA transcription correlated with increased expression of the LysR-family transcription factor leuO. Deletion of leuO restored aphA expression, and CT and TCP production, in a tolC mutant. The collective results document that tolC is required for ToxR regulon expression and further suggest that tolC may participate in a efflux-dependent feedback circuit to regulate virulence gene expression.

Role of the multiple efflux pump protein TolC on growth, morphology, and biofilm formation under nitric oxide stress in Cronobacter malonaticus

Nitric oxide (NO) is a biological signal molecule that can control and prevent the growth of most pathogens. Cronobacter species are a group of gram-negative foodborne pathogens that cause severe diseases, including neonatal meningitis, septicemia, and necrotizing enterocolitis, especially among newborns and infants consuming contaminated powdered infant formula. Cronobacter species might be tolerant to NO, resulting in severe infections. However, the specific mechanism of tolerance to NO in Cronobacter species is unclear. Here, we explore the effects of a key component, the protein TolC, of a multiple efflux pump on the growth, morphological changes, and biofilm formation of Cronobacter malonaticus under NO stress. We found that deletion of tolC resulted in a decreased growth rate under 100 mM sodium nitroprusside (NO donor) and led to more disruptive morphological injury to the bacterial cells. Furthermore, C. malonaticus lacking the TolC protein (ΔtolC mutant) showed weaker biofilm formation than the wild-type strain under normal or NO stress conditions. We have proved that TolC plays an important role in cell growth and biofilm formation of C. malonaticus. Therefore, our results may provide valuable theoretical basis for formulating clinical guidelines for treatment of disease caused by C. malonaticus and ensuring food safety.

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.

Genomic insights into evolution of pathogenicity and resistance of multidrug-resistant Raoultella ornithinolytica WM1

Raoultella ornithinolytica is a poorly understood opportunistic pathogen, and the underlying mechanisms of its multidrug resistance and pathogenicity have not yet been comprehensively investigated. The multidrug-resistant (MDR) strain WM1 was isolated from the blood of a male patient in Tianjin, China, in 2018. Here, we describe the complete genome and provide a genomic analysis of R. ornithinolytica WM1. The isolate was resistant to all tested antimicrobials except amikacin, tobramycin, and tigecycline. Two plasmids, pWM1-1 (IncHI5) and pWM1-2 (IncR), carried multidrug-resistance regions. A large antimicrobial resistance island region resided on pWM1-1 and exhibited mosaic structures resulting from the acquisition of complex integrations of variable regions, including genes conferring resistance to multiple classes of antimicrobials. Moreover, WM1 possessed virulence-related elements that encode several virulence factors, including type I fimbriae, Escherichia coli common pilus, type II and VI secretion systems, yersiniabactin, enterobactin, and surface polysaccharide, indicating pathogenic potential. Furthermore, the core genome phylogeny and pan-genome analyses revealed extensive genetic diversity. Our analysis indicates the need for stringent infection control, antimicrobial stewardship, periodic resistance monitoring, and rational medication to address potential threats posed by MDR R. ornithinolytica strains.

A Comparative Study of Fluoroquinolone-Resistant Escherichia coli Lineages Portrays Indistinguishable Pathogenicity- and Survivability-Associated Phenotypic Characteristics Between ST1193 and ST131

Background

Sequence type 1193 is a new such lineage among fluoroquinolone-resistant Escherichia coli, which has risen dramatically within the last several years. However, reasons for rapid emergence and successful spread of E. coli ST1193 remain unclear. The aim of this study was to compare the pathogenicity and survivability features of E. coli ST1193 with global epidemic lineage, ST131.

Methods

A total of 30 E. coli were used in this study. Isolates were divided into two groups, ST1193 (n=15) and ST131 (n=15). Adhesion and invasion to T24 cells and resistance to serum were quantified and compared among two groups. Biofilm formation capacity was assessed by crystal violet assay. Macrocolony formation was assessed on macrocolony formation plates. Resistance to hydrogen peroxide was performed by broth microdilution. RAW264.7 cells were used to assess the anti-phagocytic function of different isolates.

Results

Adhesion and invasion assays revealed that E. coli ST1193 could adhere and invade T24 cells (p <0.05). 93.3% of E. coli ST1193 could form biofilms. The majority of E. coli ST1193 (66.7%) possessed no curli/no cellulose on macrocolony formation plates. E. coli ST1193 showed significant growth in serum and hydrogen peroxide and illustrated higher anti-phagocytic function to RAW264.7 cells (p <0.05). Group analysis showed that E. coli ST1193 was similar to ST131 in pathogenicity- and survivability-associated phenotypic characteristics (p >0.05).

Conclusion

Our study provided more insights into pathogenicity and survivability features of E. coli ST1193, which was similar to ST131. Our study could be of great importance in understanding the emergence of global spread E. coli ST1193. Strategic and continued surveillance should be carried out to prevent the infections caused by E. coli ST1193.