tet(X4) is the critical resistance gene for tigecycline degradation that has been continually reported in recent years. In particular, pathogenic bacteria carrying tet(X4) are a severe threat to human health. However, information describing Escherichia coli coharboring tet(X4) with virulence genes is limited. Here, we isolated an E. coli strain coharboring tet(X4) and the heat-stable toxin gene astA from a dead piglet. The strain named 812A1-131 belongs to ST10. The genome was sequenced using the Nanopore and Illumina platforms. The virulence genes astA and tet(X4) are located on the chromosome and in the IncHI1-type plasmid p812A1-tetX4-193K, respectively. The plasmid could be conjugatively transferred to recipient E. coli J53 with high frequency. In vivo experiments showed that strain 812A1-131 is pathogenic to Galleria mellonella and could colonize the intestines of mice. In summary, pathogenic E. coli could receive a plasmid harboring the tet(X4) gene, which can increase the difficulty of treatment. The prevalence and transmission mechanisms of pathogenic bacteria coharboring the tet(X4) gene need more attention.

This study aimed to identify tigecycline-resistant tet(X4)-bearing Escherichia fergusonii isolated from pigs in China with a complete genome sequence. E. fergusonii was isolated by selective medium and screened from tigecycline-supplemented agar plates. The microbroth dilution method was used for antimicrobial susceptibility testing, and the minimal inhibitory concentration (MIC) results refer to the interpretation standard in the Clinical and Laboratory Standards Institute of America (CLSI). Whole-genome sequencing was performed on the Illumina HiSeq and Nanopore GridION platforms. The antimicrobial resistance (AMR) genes virulence genes and replicon types of plasmids were predicted by the CGE server. E. fergusonii EF21QZZ116 was identified from 760 faecal and caecal content samples and was resistant to tigecycline, tetracycline, ampicillin, sulfisoxazole, trimethoprim-sulfamethoxazole, spectinomycin, and florfenicol. The AMR genes tet(X4), bla_TEM-1B, and floR are located on the hybrid IncFIA-IncHI1A-IncHI1B plasmid pQZZ166-tetX-190K and are 190 391 bp in length. This hybrid plasmid has high homology with the plasmids of Escherichia coli, Enterobacter cloacae, Klebsiella, Citrobacter, and Salmonella based on comparison and analysis with the NCBI database. Notably, conjugative transfer and S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) assays show that the plasmid can transfer horizontally. To the best of our knowledge, this is the first report of E. fergusonii carrying the tet(X4) gene isolated from a pig; this report provides insight into the AMR characteristics of E. fergusonii and offers insight into public health.

Japanese encephalitis virus (JEV) is a zoonotic pathogen transmitted primarily by Culex mosquitoes and causes severe neurological diseases in humans and animals. The main endemic areas are the Western Pacific and Southeast Asia, and its geographical distribution has expanded in recent years. The development of a diagnosis for orthoflavivirus infections is hampered by two main problems: the short duration of viremia, resulting in a narrow detection window, and severe cross-reactivity. NS1, a secreted nonstructural protein of orthoflavivirus, holds promise as a new target for overcoming these limitations. In this study, we established a highly specific and sensitive capture ELISA for the JEV NS1 protein. First, the JEV NS1 protein was successfully expressed in mammalian cells and purified using affinity chromatography. Seven mAbs recognizing JEV NS1 were generated, and the mAb 20B6 exhibited the strongest binding affinity. Based on 20B6, a capture ELISA was developed with an optimal coating concentration of 3 μg/mL and an optimal detection antibody working concentration of 0.432 μg/mL. No cross-reactivity was observed with other orthoflaviviruses (including WNV, KUNV, USUV, MVEV, SLEV, and ZIKV) or common porcine viruses. The method could effectively detect NS1 protein in cell culture medium, cell lysates, mouse tissues, and porcine serum samples from JEV-infected subjects. This study provides a solid foundation that may be further developed into an efficient and specific tool for epidemiological surveillance of Japanese encephalitis.