Background: Brucellosis is a global zoonosis caused by Brucella. Histidine biosynthesis is essential for bacterial growth, but its role in Brucella melitensis virulence remains unclear. HisD catalyzes the final two steps of histidine synthesis and is absent in mammals, making it a potential drug target. Results: We constructed a hisD deletion mutant (ΔhisD) and complemented strain (ChisD) via homologous recombination. ΔhisD failed to grow in medium without histidine supplementation. It showed reduced survival under polymyxin B and SDS stress, and impaired outer membrane integrity under polymyxin B challenge, though no defect was observed under non-stressed conditions. Intracellularly, ΔhisD replicated poorly in HeLa and RAW264.7 cells, and this defect was rescued by exogenous histidine. In a mouse model, ΔhisD exhibited lower bacterial loads in liver and spleen, reduced splenomegaly, and attenuated hepatic granuloma formation. Conclusions: Histidine biosynthesis deficiency attenuates Brucella virulence by restricting nutritional acquisition and conditionally compromising outer membrane stability. HisD is a promising target for anti-brucellosis drug development, and ΔhisD holds potential as a live attenuated vaccine candidate.

Avian pathogenic Escherichia coli (APEC) can cause colibacillosis, which is economically devastating to poultry industries worldwide. The bacterial membrane is critical to its environment adaptability and virulence. The inner membrane protein TolA maintains membrane integrity, but its roles in the fitness and pathogenesis of APEC are not completely understood. Thus, a tolA gene mutant and complemented strains of APEC were constructed and characterized. Mutant strain ΔtolA showed damage in the inner and outer membranes, as well as altered morphology, impaired flagella production, reduced motility, increased outer membrane vesicle (OMV) production, and reduced resistance to antibiotics and environmental stress. Deletion of the tolA gene resulted in significant reductions in biofilm formation and interbacterial competition, due to the downregulated expression of biofilm-associated genes and type VI secretion system (T6SS) genes, respectively. In addition, the mutant strain exhibited reductions in serum bactericidal resistance, cell infection capacity, intracellular survival, consequently leading to attenuated bacterial survival and virulence in mice. Compared with the wild-type and complemented strains, the mutant strain induced less expression of inflammatory cytokine interleukin 1 beta (IL-1β) in HD-11 macrophages, consistent with the pathological damage in mice. In conclusion, inner membrane protein TolA contributes to the antibiotic resistance, environmental adaptability, biofilm formation and virulence of APEC.

The gut microbiota and its metabolites are important regulators of mucosal immunity against enteric pathogens. However, the host pathways that coordinate intestinal microbial ecology, bile acid metabolism, and antibacterial defense remain incompletely understood. STING is a key adaptor in nucleic acid sensing, but its role in shaping the intestinal microbial-metabolic environment during bacterial infection is unclear. Wild-type and STING-deficient mice were compared in an oral Salmonella enterica serovar Typhimurium infection model. Disease severity was assessed by survival, body weight change, histopathology, bacterial burden, serum cytokines, and flow cytometry. The microbiota and metabolite profiles of colonic luminal contents, together with host transcriptional responses in distal colon tissue, were analyzed using 16 S rRNA gene sequencing, untargeted LC-MS/MS metabolomics, RNA sequencing, and integrative multi-omics analyses. STING-deficient mice showed increased susceptibility to Salmonella infection, including reduced survival, greater body weight loss, higher bacterial burdens, more severe intestinal pathology, along with impaired intestinal barrier integrity, and increased inflammatory cytokine production. STING deficiency was associated with reduced microbial diversity and altered gut microbial composition, including enrichment of infection-associated taxa such as Parabacteroides and depletion of commensal genera such as Turicibacter and Lactobacillus. Metabolomic profiling revealed remodeling of the intestinal metabolic landscape, with prominent alterations in bile acid- and lipid-related metabolites. Host transcriptomic analysis showed reduced expression of genes and pathways related to MHC class II antigen presentation and T cell activation. Cross-omics correlation analyses linked altered microbial taxa and bile acid metabolites with impaired mucosal immune gene expression. These findings identify STING as a host factor associated with intestinal microbial and bile acid metabolic homeostasis during Salmonella infection. STING deficiency is associated with coordinated alterations in gut microbial composition, bile acid metabolism, mucosal immune transcriptional programs, and host susceptibility to enteric infection.

Avian pathogenic Escherichia coli (APEC) is a major poultry pathogen that causes colibacillosis and imposes a substantial economic burden on global poultry production. Human extraintestinal pathogenic Escherichia coli (ExPEC) and APEC exhibit comparable serotypes, phylogenetic lineages, and virulence-associated gene profiles. Moreover, APEC acts as a source of virulence determinants and antimicrobial resistance genes that are also relevant to human ExPEC infections. We identified a pentatricopeptide repeat (PPR) protein EspX1 in APEC, but its function is unknown. The espX1 gene mutant and complemented strains of APEC were constructed and characterized. The results showed that EspX1 did not affect APEC growth or motility. The espX1 deletion mutant exhibited enhanced biofilm formation and cell adhesion but reduced serum resistance and intracellular survival. Furthermore, the mutant strain showed decreased colonization capacity in the liver and spleen during systemic infection and attenuated virulence in vivo. Additionally, EspX1 was found to inhibit the expression of inflammatory cytokines TNF-α, IL-1β, and IL-8 in host cells. These findings suggest that EspX1 plays a crucial role in the pathogenicity of APEC by modulating multiple virulence-related phenotypes and host immune responses. Moreover, EspX1 enhanced APEC resistance to ciprofloxacin. This study provides novel insights into PPR proteins functions in prokaryotes and lays a theoretical foundation for the development of new strategies to control APEC infections.

Conjugated linoleic acid (CLA) is a dietary lipid that modulates host-microbiota-immune interactions, yet its mechanistic impact on mucosal defense remains unclear. Here, we show that oral CLA supplementation enhances resistance to Salmonella Typhimurium infection and is associated with coordinated changes in gut microbial composition and mucosal immune responses. CLA-enriched commensals, including Dubosiella and Lactobacillus, were associated with increased production of CLA-derived oxylipins and activation of immune surveillance genes. Functionally, CLA pretreatment reduced Salmonella colonization, preserved epithelial integrity, and decreased neutrophilic inflammation without direct antibacterial effects. Single-cell RNA sequencing of ileal intraepithelial lymphocytes revealed that CLA predominantly reprogrammed intestinal CD8⁺ T cells toward an oxidative phenotype and enhanced effector activity. ATAC-seq revealed increased chromatin accessibility at loci associated with metabolic regulation, consistent with transcriptional reprogramming toward oxidative fitness. Mechanistically, CLA directly activated PPARγ signaling to promote mitochondrial biogenesis, oxidative phosphorylation, and the production of IFN-γ and granzyme B in CD8⁺ T cells; pharmacologic inhibition of PPARγ attenuated these effects both in vitro and in vivo. Notably, depletion of CD8⁺ T cells eliminated CLA-mediated protection and abolished early restriction of bacterial dissemination at Peyer's patches and mesenteric lymph nodes. Although CLA enhanced CD8⁺ T-cell effector programs, antibiotic depletion and fecal microbiota transplantation experiments demonstrated that an intact gut microbiota is necessary for effective protection in vivo. Together, these findings identify CLA as a dietary modulator that strengthens mucosal resistance to Salmonella by promoting PPARγ-mediated metabolic reprogramming and enhanced effector fitness in intestinal CD8⁺ T cells.

Brucellosis caused by Brucella melitensis is a worldwide zoonotic disease, yet the role of the c-di-GMP phosphodiesterase BpdB in virulence remains incompletely understood. This study aimed to investigate the function of BpdB in B. melitensis pathogenicity and its involvement in host STING signaling. A bpdB deletion strain (ΔbpdB) and a complemented strain (CbpdB) were constructed in B. melitensis M5. Bacterial growth, stress tolerance, intracellular survival in macrophages, cytokine expression, and mouse virulence were evaluated. Deletion of bpdB did not affect in vitro growth but significantly attenuated virulence in BALB/c mice, reducing splenomegaly, splenic bacterial load, and hepatic granuloma formation. The ΔbpdB strain exhibited enhanced sensitivity to oxidative stress, whereas resistance to acid, polymyxin B, and SDS remained unchanged. Intracellular survival of ΔbpdB in RAW264.7 macrophages was reduced at 72 h post infection, a defect that was completely abrogated in STING-knockout RAW264.7 cells. ΔbpdB infection induced higher transcriptional levels of IFN-β and IL-1β, with IFN-β induction strictly dependent on STING. In C57BL/6J mice, the virulence attenuation of ΔbpdB was partially STING-dependent, as the reduction in splenic bacterial load was smaller in STING-knockout than in wild-type mice. These findings demonstrate that BpdB contributes to B. melitensis virulence by enhancing oxidative stress resistance and dampening STING-dependent host responses, providing new insights into c-di-GMP-mediated host-pathogen interactions.

Avian pathogenic Escherichia coli (APEC) severely impedes the development of the poultry industry and poses a serious threat to public health. The LuxS affects physiological processes such as bacterial virulence, biofilm formation, environmental adaptability, and motility. However, the effects of the LuxS on the environmental adaptability of APEC are not fully understood. Our study aims to investigate the effects of the LuxS on the environmental adaptability of APEC. Thus, the luxS gene mutant and complemented strains of APEC were constructed and characterized. We found that the mutant strain ΔluxS exhibited impaired adaptability to environmental stress, including oxidative, acid, base, heat, and hyperosmotic stress, with corresponding downregulation of stress-responsive genes. For oxidative stress tolerance, marA, fldA, and the rseC gene in the SoxR reduction system showed reduced expression. Genes regulating membrane and acid-base homeostasis, pH-inducible proteins, and the EvgS/EvgA two-component system were downregulated for acid-base stress. Genes related to osmoprotectant synthesis, uptake, potassium regulation, and heat stress adaptability, including extra cytoplasmic stress response (ESR), also exhibited lower transcriptional levels. Furthermore, we found that the ΔluxS mutant strain was impaired in competition capability due to downregulation of type VI secretion system (T6SS) genes. In addition, the mutant strain exhibited lower outer membrane permeability and lower proton motive force (PMF) compared with the wild-type strain. In conclusion, these findings indicate that the LuxS plays a critical role in regulating environmental adaptability, competition capability, outer membrane permeability, and PMF maintenance in APEC.

Cyclic di-GMP (c-di-GMP) is a universal bacterial second messenger that orchestrates the transition between motile and sessile lifestyles, thereby shaping microbial physiology, virulence, and persistence. In Escherichia coli (E. coli), c-di-GMP functions as a central integrator of environmental cues, dynamically regulating motility, biofilm formation, energy metabolism, and pathogenicity. Here, we provide a comprehensive synthesis of recent advances in c-di-GMP signaling in E. coli, spanning local signaling modules that control curli and cellulose biosynthesis to global regulatory circuits linking central metabolism, stress adaptation, and virulence gene expression. We further highlight the emerging view of c-di-GMP as a pathogen-associated molecular pattern that interfaces with host immune sensors such as STING and DDX41, extending its biological relevance beyond bacterial physiology. Finally, we discuss the translational potential of targeting c-di-GMP signaling for biofilm disruption, enhancement of bacteriophage-mediated clearance, and vaccine adjuvant design. Collectively, this review positions E. coli as a powerful model to decode the multifaceted biology of c-di-GMP and to inspire novel antimicrobial and immunomodulatory strategies.

Brucella melitensis, a facultative intracellular pathogen, relies on membrane integrity and homeostasis to resist host defenses and establish infection. The plsC gene encodes 1-acyl-sn-glycerol-3-phosphate acyltransferase, a key enzyme in the glycerophospholipid pathway that catalyzes the synthesis of phosphatidic acid, an essential precursor for membrane lipid formation. However, its role in B. melitensis virulence remains poorly understood. Here, we constructed a plsC deletion mutant (ΔplsC) and a complemented strain (ΔplsC-Com) in B. melitensis strain M5 and characterized their phenotypes. Deletion of plsC impaired bacterial growth in nutrient-limited media, reduced tolerance to hydrogen peroxide and polymyxin B, and decreased lipid synthesis while increasing outer membrane permeability. Ultrastructural analysis revealed surface roughness, cytoplasmic voids, and nucleoid condensation in the mutant. Although ΔplsC retained normal adhesion and invasion capabilities in RAW264.7 macrophages and HeLa cells, its intracellular survival was specifically attenuated in macrophages at 48 h post-infection. In a mouse model, ΔplsC showed significantly reduced colonization of the spleen and liver and induced fewer and smaller liver granulomas as compared with the parental and complemented strains. These results demonstrate that PlsC is essential for maintaining membrane homeostasis and stress resistance in Brucella, which in turn supports its survival within professional phagocytes and full virulence in vivo. Our study suggests a critical link between phospholipid metabolism and Brucella pathogenicity.

Avian pathogenic Escherichia coli (APEC) induces avian colibacillosis and brings huge economic losses to global poultry production. The small alarmone (p)ppGpp mediates the bacterial stringent response, a vital pathway modulating microbial stress adaptation and pathogenic capacity. The functions of the (p)ppGpp synthase gene relA in APEC pathogenesis remain poorly characterized. In this study, we constructed a relA deletion mutant (ΔrelA) and its complemented strain (CΔrelA). The phenotypic and pathogenic characteristics of these strains were investigated. The results showed that deletion of relA did not significantly affect bacterial growth or motility. However, the ΔrelA strain showed increased susceptibility to aminoglycoside antibiotics. Furthermore, the enhanced interbacterial competition of the mutant was associated with the upregulation of core genes in the type VI secretion system (T6SS). Importantly, relA was essential for APEC adhesion to and invasion of avian DF-1 cells, as well as for colonization and virulence in ducklings, where ΔrelA exhibited significantly attenuated infectivity and reduced bacterial loads in the liver and spleen. Furthermore, transcriptomic analysis revealed that RelA deletion downregulated genes involved in integral components of the membrane, and further assays confirmed compromised membrane integrity in the mutant strain. These findings suggest that RelA maintains membrane integrity, which underpins its contributions to antibiotic resistance and virulence. These findings indicate that relA plays a key role in APEC virulence, antibiotic resistance, and membrane homeostasis, and could provide a theoretical basis for targeting the stringent response as a potential strategy to control avian colibacillosis.

Non-typhoidal salmonellosis, caused by Salmonella enterica, threatens poultry production and food safety in East Africa, where poultry is vital for livelihoods. This systematic review and meta-analysis assessed the pooled prevalence, serotype distribution, and antimicrobial resistance patterns of non-typhoidal Salmonella in East African poultry. Following PRISMA guidelines, we searched on PubMed, Web of Science, Scopus, African Journals Online, and Google Scholar for studies published up to December, 2025. A random-effects model was used to calculate pooled prevalence with 95% confidence intervals in R (Version 4.6.0). Subgroup analyses and I2 statistics were used to explore the source of heterogeneity, and a heatmap visualized the antibiotic resistance patterns. Thirteen studies comprising 422 positive isolates were included. The pooled prevalence of non-typhoidal Salmonella in East Africa was 6% (95% CI: 4-8%), with high heterogeneity (I2 = 95.3%). The subgroup analysis showed prevalence was highest in Uganda (11%, 95% CI: 7-16%) and lowest in Tanzania (1%, 95% CI: 0-6%). By diagnostic method, slide agglutination was higher (7%, 95% CI: 5-10%) than PCR (4%, 95% CI: 1-8%). By sample type, internal organs had the highest prevalence (17%, 95% CI: 12-21%) and environmental samples had the lowest (1%, 95% CI: 0-3%). By source, slaughterhouses recorded the highest rate (12%, 95% CI: 7-18%) and extensive farms the lowest rate (3%, 95% CI: 0-8%). The pooled antibiotic resistance was 65% (95% CI: 55-79%). Oxytetracycline is the most resistant antibiotic (84%, 95% CI: 70-98%). S. Typhimurium exhibited the highest pooled prevalence (18%, 95% CI: 15-22%), and S. Kentucky was the most multidrug-resistant serotype and had the highest number of resistance genes. In conclusion, non-typhoidal Salmonella is prevalent in East African poultry, with multidrug-resistant serotypes distributed across the region. Therefore, collaborative interventions are urgently needed to address this zoonotic threat.

Multidrug-resistant (MDR) bacteria have reduced the effectiveness of antimicrobial agents and limited available treatment options in both human and animal settings. Antimicrobial resistance (AMR) in animal-derived Escherichia coli (E. coli) has become increasingly common, with many isolates showing resistance to multiple classes of antimicrobials. However, compared with other animal sources, resistance characteristics of E. coli from mink remain less well understood, particularly in terms of genomic features. In this study, we identified a MDR E. coli strain, EC0D1, isolated from the lung tissue of a farmed mink that succumbed to hemorrhagic pneumonia (HP) in China. Antimicrobial susceptibility testing indicated that EC0D1 exhibited resistance to β-lactams, fluoroquinolones, aminoglycosides, tetracyclines, and polymyxins but was sensitive to carbapenems and tigecycline. Whole genome sequencing showed that EC0D1 contains a single chromosome and eight plasmids. Among these, plasmid pEC0D1-3 coharbored blaCTX-M-55 and mcr-1.1, while pEC0D1-2 carried tet(A) and floR, together explaining the observed MDR phenotype. Phylogenetic analysis classified EC0D1 as sequence type ST457 and demonstrated a close genetic relationship with several human clinical isolates. Comparative genomic analysis further revealed that plasmids pEC0D1-2 and pEC0D1-3 shared high sequence similarity with plasmids previously identified in avian-derived E. coli and human-derived Klebsiella pneumoniae isolates. Conjugation assays confirmed that plasmids carrying blaCTX-M-55, mcr-1.1, tet(A), and floR were transferable to different bacterial recipients. The emergence of transferable resistance determinants in mink-associated E. coli suggests a potential role in the transmission of resistance genes between human and animal hosts.

The Mycoplasmataceae are a family of bacteria that typically cause respiratory, arthritic, and genitourinary disease in humans. Mycoplasma spp. of animal origin are also the causative agents of porcine wheezing disease, chronic respiratory disease and arthritis in chickens and other conditions. These diseases have a significant impact on public health and the economic development of livestock breeding. Clinical prevention and treatment of mycoplasma infections is primarily dependent on the use of antibiotics. However, inappropriate and excessive use of antimicrobials has enabled resistance development that has become a significant clinical concern. Mycoplasma are also robust biofilm producers, and this process is a major factor for the persistence of these infections, especially in conjunction with common antibiotic resistance mechanisms, including target gene mutations and the action of efflux pumps. A mycoplasma biofilm refers to a structured and stable microbial community formed by Mycoplasma spp. adhering to biological or non-biological surfaces under suitable conditions and secreting extracellular polymers (EPS) such as polysaccharides. This process allows the microorganisms to adapt to their surrounding environment and survive during the growth process. These biofilms render bacteria more resistant to antimicrobials than planktonic bacteria, resulting in biofilm-associated infections that are more challenging to eradicate and more likely to recur. The current study reviews progress from the fields of biofilm formation, structure and identification, correlations between biofilms and drug resistance and virulence as well as methods of biofilm prevention and control. Our aim was to provide a reference basis for the subsequent in-depth understanding of the research of mycoplasma biofilms.

Mycoplasma synoviae (MS) is considered to be one of the main mycoplasma pathogens of poultry, causing arthritis, airsacculitis, eggshell apex abnormalities and production drops in chickens and turkeys. Infection by MS usually results in considerable economic losses to the poultry industry worldwide. Therefore, it is essential to develop a highly sensitive and accurate diagnostic method in the livestock production. The MSLP53 was predicted as a highly conserved and specific membrane associated lipoprotein of MS by bioinformatics analysis. The His-tagged MSLP53 (rMSLP53) protein was expressed and purified using E. coli expression system, and was confirmed by Western blotting to react with each MS-positive serum, but not react with positive sera against other avian pathogens, suggesting that the rMSLP53 had strong immunoreactivity and specificity. An rMSLP53-based indirect ELISA was developed, compared to IDEXX kit with a pool of 277 chicken sera samples, and showed high sensitivity (85.54

Mycoplasma synoviae (MS) is a globally prevalent avian pathogen responsible for airsacculitis and synovitis. The temperature-sensitive (ts)+ vaccine strain MS-H, a live attenuated variant, is the most effective and widely used vaccine for controlling infections in the poultry industry. Consequently, accurate detection is essential for a strategy known as differentiating infected from vaccinated animals (DIVA). In this study, we developed a duplex real-time TaqMan minor groove binder (MGB) probe PCR (The DRTM-probe PCR) method to differentiate the MS-H live vaccine strain from wild-type strains by targeting a single nucleotide polymorphism (SNP) in the ktrB gene. This gene overcomes the restoration of the genotype of wild-type 86079/7NS in specific regions. With a detection limit of 6.25 copies/μL, the DRTM-probes PCR method demonstrates a good specificity in distinguishing in one hour. For simulated clinical samples, the method achieved over 95 % sequence identity with reference fragments, confirming its accuracy. The established DRTM-probe PCR method offers a specific, rapid, and reliable approach for SNP detection with significant application potential.

Brucellosis, a globally significant zoonotic disease caused by Brucella infection, relies on the pathogen’s ability to invade and replicate within host cells. This intracellular replication is tightly regulated by transcriptional networks, including the LysR-family regulator VtlR, which is critical for B. abortus virulence but whose role in B. melitensis remains unclear. Here, we constructed vtlR mutant and complemented strains in B. melitensis M5 and demonstrated that VtlR is essential for virulence. Phenotypic assays revealed that vtlR deletion impaired bacterial growth on L-fucose, D-glucose, and meso-erythritol, increased sensitivity to hydrogen peroxide and sodium nitroprusside, and reduced intracellular survival in RAW264.7 macrophages while triggering reactive oxygen species (ROS) production. RNA-seq and RT-qPCR analysis indicated that VtlR positively regulates small RNA AbcR2 and three DUF1127-domain proteins (RS13565, RS04310, RS13280), mirroring its regulatory role in B. abortus. However, overexpression of these targets failed to restore virulence in the vtlR mutant. Notably, the mutant strain elicited protective immunity in mice, suggesting its potential as a live-attenuated vaccine candidate. Collectively, this study elucidates the VtlR regulon in B. melitensis, advancing our understanding of Brucella pathogenesis and vaccine development.

The widespread chronic enteritis known as Paratuberculosis (PTB) or Johne's disease (JD) is caused by Mycobacterium avium subspecies paratuberculosis (MAP), posing a significant threat to global public health. Given the challenges associated with PTB or JD, the development and application of vaccines are potentially important for disease control. The aim of this study was to design a multi-epitope vaccine against MAP. A total of 198 MAP genomes were analyzed using pan-genome and reverse vaccinology approaches. B-cell and T-cell epitope analysis was performed on the selected promising cross-protective antigens followed by selection of epitopes with high antigenicity, no allergenicity, and no toxicity for the design of the vaccine. The designed vaccine was evaluated through molecular dynamics simulations, molecular docking, and immunological simulations. The results revealed the identification of five promising cross-protective antigens. In total, 10 B-cell epitopes, 10 HTL epitopes, and 9 CTL epitopes were selected for the design of the vaccine. Both the vaccine candidate and the vaccine-TLR4 complex demonstrated considerable stability in molecular dynamics simulations. Molecular docking studies confirmed that the vaccine candidate successfully interacted with TLR4. Immunological simulations showed an increase in both B-cell and T-cell populations after vaccination. Additionally, the vaccine candidate exhibited a codon adaptability index of 1.0 and a GC content of 53.64%, indicating strong potential for successful expression in Escherichia coli. This research developed a multi-epitope vaccine targeting MAP through pan-genomes and reverse vaccinology methods, offering innovative strategies for creating effective vaccines against MAP.

BackgroundPathogens employ a variety of effectors to modulate key host signaling pathways, thereby facilitating bacterial survival and enhancing pathogenicity. Despite lacking a complete ubiquitin system of their own, bacterial effectors frequently function as ubiquitin ligases or deubiquitinases (DUBs) to disrupt the eukaryotic ubiquitin machinery. DUBs have been found in a variety of bacteria, including ElaD, which has recently been recognized as a DUB in Escherichia coli (E. coli). However, the distribution and evolutionary analyses of ElaD in different E. coli remains largely unknown.MethodsWe retrieved and analyzed the elaD gene sequences of 530 E. coli strains. Then, molecular characterization of each strain was determined. According to all the statistical information, the distribution of elaD gene in E. coli was comprehensively investigated, and the relationship between elaD and E. coli pathotypes, serotypes, phylogenetic groups and MLSTs was analyzed. Phylogenetic tree was also constructed to analyze the evolutionary relationships between different ElaD.ResultsOur findings demonstrate that the elaD gene was present in 66.60% (353/530) of both pathogenic and nonpathogenic E. coli strains. elaD gene is predominantly found in the O157, O26, O139 and O8 serotypes. The majority of elaD-positive strains belonged to phylogenetic groups B1, A, E and D, with the predominant sequence types being ST11, ST21, ST10, ST1 and ST69. ElaD from different strains clustered in the phylogenetic tree in a correlation with O serotypes and phylogenetic groups. In addition, ElaD of some branches showed premature translation termination.ConclusionThe widespread occurrence of the elaD gene among various E. coli strains suggests its potential significance in E. coli, although its precise functional role remains to be elucidated.

Avian pathogenic Escherichia coli (APEC) can infect poultry and cause colibacillosis, leading to significant economic losses in the poultry industry. APEC is similar to human Extraintestinal pathogenic Escherichia coli (ExPEC) in serotype, phylogenetic clustering and virulence genes, and is a repository of ExPEC virulence and drug resistance genes. We identified a pentatricopeptide repeat (PPR) protein EspX1 in APEC, but its function is unknown. The espX1 gene mutant and complemented strains of APEC were constructed and characterized. The results showed that EspX1 does not affect the growth or motility of APEC. The espX1 deletion mutant exhibited enhanced biofilm formation and cell adhesion but reduced serum resistance and intracellular survival. Furthermore, the mutant strain showed decreased colonization in the liver and spleen during systemic infection and attenuated virulence in vivo. Additionally, EspX1 was found to inhibit the expression of inflammatory cytokines TNF-α, IL-1β, and IL-8 in host cells. These findings suggest that EspX1 plays a crucial role in the pathogenicity of APEC by modulating multiple virulence-related phenotypes and host immune responses. In addition, EspX1 enhances APEC resistance to ciprofloxacin. This study provides novel insights into the functions of PPR proteins in prokaryotes and lays a theoretical foundation for developing new strategies to control APEC infections.

The inappropriate use of cephalosporins lead to the occurrence and global spread of bacteria resistant to these antimicrobials. In this study, we isolated four Escherichia albertii strains from broilers in eastern China. The antimicrobial susceptibility and genomic characterization of these E. albertii isolates were determined. Our results revealed that these four E. albertii isolates exhibited resistance to tetracyclines, chloramphenicol, beta-lactams, aminoglycosides, polymyxin B, sulfonamides, quinolones, and other antimicrobials. Among them, EA04 isolate was multidrug resistant and harbored extended-spectrum beta-lactamases (ESBL) genes blaCTX-M and blaTEM. Whole genome sequencing and core-genome multilocus sequence typing (cgMLST) based on all ST4638 E. albertii for EA04 inferred highly probable epidemiological links between selected human isolates. Additionally, the ESBL genes blaTEM-141 and blaCTX-M-55 were coexistent in an approximately 75 kb IncFII plasmid pEA04.2 in EA04. Comparative analysis indicated that genes blaTEM-141 and blaCTX-M-55 were located in IS15-blaCTX-M-55-wbuC-blaTEM-141-IS26 region, which similar structures were identified in various bacteria. Furthermore, the plasmid pEA04.2 could be transferable to E. coli EC600 and lead to the resistance to third-generation cephalosporins. These results suggested that chicken potentially serve as a reservoir for multidrug resistant E. albertii, which increases the risk of horizontal transfer of antimicrobial resistance between humans, animals and environment.