Aug 2026· Microorganisms· Vol 14, pp. 1803· 0 citations· 34 references
Medicine
TL;DR
It is indicated 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.
Abstract
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.
Avian pathogenic Escherichia coli (APEC) is a major cause of colibacillosis in poultry, yet the role of the ecpA gene, which encodes the major structural subunit of the Escherichia coli common pilus (ECP), remains incompletely defined in APEC pathogenesis. To investigate the role of ecpA in the biological characteristics and pathogenicity of Avian Pathogenic Escherichia coli (APEC) strain FJLY68, an ecpA deletion mutant (ΔecpA) and its corresponding complemented strain (CΔecpA) were constructed using the CRISPR/Cas9 system and verified by PCR and Sanger sequencing. Phenotypic analyses revealed that the ΔecpA mutation significantly impaired bacterial motility, biofilm formation, adherence to chicken embryonic fibroblast (DF-1) cells, and fimbriae assembly. Transcriptomic analysis identified 1720 differentially expressed genes in the ΔecpA mutant, significantly enriched in pathways associated with flagellar assembly, chemotaxis, and metabolism, consistent with the observed phenotypic changes. Although in vitro growth was unaffected, the ΔecpA mutant exhibited markedly attenuated virulence in a chick infection model, as indicated by an increased LD50, attenuated clinical signs and pathological lesions, and reduced bacterial colonisation in tissues. Full genetic complementation restored all observed defects to wild-type levels. This study identifies ecpA as a critical determinant of APEC pathogenesis, directly linking its function to bacterial motility, biofilm formation, adhesion, and in vivo virulence, and provides a theoretical basis for developing novel control strategies targeting this virulence factor.
YgeP plays a central role in APEC pathogenesis by balancing two infection strategies: motility-mediated dissemination and colonization, and biofilm-mediated attachment and tolerance, and negatively regulates key virulence traits during the early stages of infection.
Weiyang Su, Zhe Li, Siqi Feng et al.· Veterinary Microbiology· 0 citations
Klebsiella pneumoniae (K. pneumoniae) is a major opportunistic pathogen associated with a broad spectrum of hospital-and community-acquired infections. Biofilm formation contributes to bacterial persistence, stress tolerance, and host immune clearance. In this study, we constructed a transposon mutant library of the clinical K. pneumoniae strain KP20 using a mariner-based mutagenesis system and screened for mutants exhibiting defective biofilm formation. Targeted knockout of thrA significantly reduced biofilm formation and attenuated the adhesion and invasion of K. pneumoniae with respect to human airway epithelial Calu-3 cells and lung adenocarcinoma A549 cells. These phenotypic changes are associated with altered transcription of the gene clusters responsible for type I and type III fimbria biosynthesis. Moreover, deletion of thrA compromised bacterial tolerance to acidic and alkaline stresses and increased susceptibility to phagocytosis by dendritic cells. In a murine infection model, thrA deletion significantly attenuated the virulence of K. pneumoniae and decreased bacterial colonization in target organs. Collectively, these findings indicate that thrA substantially contributes to biofilm formation, pH stress tolerance, host–cell interaction, and virulence in K. pneumoniae.
Deletion of fabR reduced host cell adherence, increased serum sensitivity, enhanced IgG deposition, and decreased vitronectin binding compared with the wild-type strain, and ΔfabR mutants from multiple NTHi strains showed increased metabolic activity, indicating a conserved role for FabR in metabolic regulation.
Martina Janoušková, Yu-Ching Su, Sandra Jonsson et al.· Journal of Infectious Diseas...· 0 citations
Persistence – i.e., the ability to exist in a metabolically inactive form – allows bacteria to accumulate genetic advantages. The evolution of the pathogenic potential of Klebsiella pneumoniae has led to the emergence of strains simultaneously characterized by increased aggressiveness (virulence) and prolonged survival in the host organism. This combination of properties contributes to the emergence of “superbugs,” necessitating the search for specific markers that would make it possible to prevent the spread of highly adaptive clones. Hypervirulent K. pneumoniae (hvKp) strains represent a growing global health threat, since they combine high invasiveness and antibiotic resistance. An analysis of 92 K. pneumoniae clinical isolates was conducted to assess the prevalence of the key hypervirulence genes (iroB, peg-344, rmpA, rmpA2, and iucA) and investigate their association with the bacterial persister formation gene ptsH. It was found that 64.1% (59/92) of the isolates carried at least one hvKp gene, iucA being the most frequent one (62.0%). The full set of five hvKp genes was identified in only one case (1%). The strains of sequence types ST23, ST268, ST86, ST534, ST219, ST101, and ST395 accumulated virulence genes, whereas ST512 and ST14 rarely harbored hvKp genes. A key finding was the detection of a significant association between the presence of the ptsH gene (found in 50% of the strains) and the accumulation of hvKp genes: the ptsH-positive strains were statistically more likely to harbor the complete aerobactin operon (iucABCD), in combination with one or more additional hypervirulence genes, compared to the ptsH-negative strains (p < 0.05). Our findings indicate that the ptsH gene is crucial in the formation of polygenically determined hypervirulence, and that its role in controlling bacterial persistence creates evolutionary advantages under stress induced by antibiotics or immune factors, thus promoting evasion of their actions. The phosphotransferase system (PTS), to which the ptsH gene belongs, can potentially become a novel source of molecular targets for the therapy of infections caused by hypervirulent K. pneumoniae strains.
A. Tutelyan, N. V. Vlasenko, V. M. Pisarev et al.· Acta Naturae· 1 citation
