Role of cpxA Mutations in the Resistance to Aminoglycosides and ß-Lactams in Salmonella enterica serovar Typhimurium.

Although it has been reported that deletion of the response regulator, CpxR, in the CpxRA system confers sensitivity to aminoglycosides (AGAs) and ß-lactams in Salmonella enterica serovar Typhimurium, the regulatory effects of CpxA on multidrug resistance (MDR) are yet to be fully investigated in this organism. Here, to explore the role of CpxA in MDR, various cpxA mutants including a null mutant (JSΔcpxA), a site-directed mutant (JSΔcpxA 38) and an internal in-frame deletion mutant (JSΔcpxA92 - 104 ) of the S. enterica serovar Typhimurium strain JS, were constructed. It was revealed that cpxA and cpxR deletion mutants have opposing roles in the regulation of resistance to AGAs and ß-lactams. Amikacin and cefuroxime can activate the CpxRA system, which results in increased resistance of the wild-type compared with the cpxR deletion mutant. All the cpxA mutations significantly increased resistance to AGAs and ß-lactams due to CpxRA system activation via the phosphorylation of CpxR. Moreover, AckA-Pta-dependent activation of CpxR increased the antibiotic resistance of cpxA deletion mutants. Further research revealed that the AcrAB-TolC conferred resistance to some AGAs and ß-lactams but does not influence the regulation of resistance by CpxRA against these antibiotics. The detection of candidate MDR-related CpxR regulons revealed that the mRNA expression levels of spy, ycca, ppia, htpX, stm3031, and acrD were upregulated and that of ompW was downregulated in various cpxA mutants. Furthermore, the expression levels of nuoA and sdhC mRNAs were downregulated only in JSΔcpxA92 - 104 . These results suggested that cpxA mutations contribute to AGAs and ß-lactams resistance, which is dependent on CpxR.

The Infection of the Japanese Encephalitis Virus SA14-14-2 Strain Induces Lethal Peripheral Inflammatory Responses in IFNAR Deficiency Mice.

The Japanese encephalitis virus (JEV) is a leading cause of mosquito-borne viral encephalitis worldwide. Clinical symptoms other than encephalitis, on the other hand, are substantially more prevalent with JEV infection, demonstrating the relevance of peripheral pathophysiology. We studied the peripheral immunopathogenesis of JEV using IFNAR deficient (IFNAR-/-) mice infected with the SA14-14-2 strain under the BSL-2. The body weight and survival rate of infected-IFNAR-/-mice decreased significantly. Infected-IFNAR-/-mice's liver and spleen demonstrated obvious tissue damage and inflammatory cell infiltration. There was also extensive viral replication in the organs. IFN-α/ß protein expression was dramatically elevated in peripheral tissues and serum, although the related interferon-stimulated genes (ISGs) remained low in the spleen and liver of infected-IFNAR-/-animals. Consistently, the differentially expressed genes (DEGs) analysis using RNA-sequencing of spleens showed inflammatory cytokines upregulation, such as IL-6, TNF-α, and MCP-1, and IFN-γ associated cytokine storm. The infiltration of macrophages and neutrophils in the spleen and liver of SA14-14-2-infected IFNAR-/- mice was dramatically elevated. However, there was no significant difference in tissue damage, viral multiplication, or the production of IFNα/ß and inflammatory cytokines in the brain. Infection with the JEV SA14-14-2 strain resulted in a lethal peripheral inflammatory response and organ damage without encephalitis in IFNAR-/- mice. Our findings may help shed light on the peripheral immunopathogenesis associated with clinical JEV infection and aid in developing treatment options.

Development of a Method for Simultaneous Generation of Multiple Genetic Modification in Salmonella enterica Serovar Typhimurium.

To comprehensively analyze bacterial gene function, it is important to simultaneously generate multiple genetic modifications within the target gene. However, current genetic engineering approaches, which mainly use suicide vector- or λ red homologous recombination-based systems, are tedious and technically difficult to perform. Here, we developed a flexible and easy method to simultaneously construct multiple modifications at the same locus on the Salmonella enterica serovar Typhimurium chromosome. The method combines an efficient seamless assembly system in vitro, red homologous recombination in vivo, and counterselection marker sacB. To test this method, with the seamless assembly system, various modification fragments for target genes cpxR, cpxA, and acrB were rapidly and efficiently constructed in vitro. sacBKan cassettes generated via polymerase chain reaction were inserted into the target loci in the genome of Salmonella Typhimurium strain CVCC541. The resulting pKD46-containing kanamycin-resistant recombinants were selected and used as intermediate strains. Multiple target gene modifications were then carried out simultaneously via allelic exchange using various homologous recombinogenic DNA fragments to replace the sacBKan cassettes in the chromosomes of the intermediate strains. Using this method, we successfully carried out site-directed mutagenesis, seamless deletion, and 3 × FLAG tagging of the target genes. This method can be used in any bacterial species that supports sacB gene activity and λ red-mediated recombination, allowing in-depth functional analysis of bacterial genes.

Genetic diversity, antimicrobial resistance and extended-spectrum ß-lactamase type of Escherichia coli isolates from chicken, dog, pig and yak in Gansu and Qinghai Provinces, China.

OBJECTIVES: In this study, the genetic diversity, phylogenetic grouping, antimicrobial resistance and extended-spectrum ß-lactamase (ESBL) types of Escherichia coli isolates from chickens, dogs, pigs and yaks in six prefectures of Gansu and Qinghai Provinces, China, were investigated. METHODS: E. coli was isolated from diarrhoeic and healthy faecal samples. Multilocus sequence typing (MLST), phylogenetic grouping, antimicrobial resistance and ESBL profiles were investigated. RESULTS: A total of 142 MLST sequence types (STs) were identified from 400 E. coli isolates. eBURST clustering analysis resolved the 142 STs into 19 clonal complexes (CCs) and 67 singletons. PCR phylogenetic typing determined the isolation rate of potentially pathogenic B2/D group isolates among all E. coli to be 12.5% from healthy animal samples and 17.5% from diarrhoeic samples. Antimicrobial susceptibility testing revealed 78 antimicrobial resistance patterns. E. coli resistance rates were highest to doxycycline, ampicillin and tetracycline, whereas polymyxin B and meropenem had the lowest resistance rates. All polymyxin B-resistant E. coli isolates were positive for the mcr-1 gene. A total of 62 ESBL-producing isolates were identified. The ESBL prevalence was 55.0% in diarrhoeic samplings and 5.6% in healthy animals. TEM (82.3%) was the predominant ESBL type, followed by CTM (43.5%) and SHV (19.4%). CONCLUSION: E. coli isolates in the study area have a high diversity of genetic and antimicrobial resistance patterns but a relatively low isolation rate of potentially pathogenic phylogroups. However, the somewhat high isolation rate of multidrug-resistant E. coli, particularly ESBL-producing isolates, requires continual surveillance of E. coli from animals in these areas.