Tigecycline-resistance mechanisms and biological characteristics of drug-resistant Salmonella Typhimurium strains in vitro.

Increased drug resistance of Gram-negative bacteria to tetracycline caused by the unreasonable overuse of tigecycline has attracted extensive attention to reveal potential mechanisms. Here, we identified a tigecycline-resistant strain called TR16, derived from Salmonella Typhimurium ATCC13311 (AT), and examined its biological characteristics. Compared with AT, the TR16 strain showed significantly higher resistance to amoxicillin but lower resistance to gentamicin. Although the growth curves of TR16 and AT were similar, TR16 showed a significantly increased capacity for biofilm formation and a notably decreased motility compared to AT. Furthermore, transcriptome sequencing and reverse transcription-quantitative PCR (RT-qPCR) were implemented to evaluate the genetic difference between AT and TR16. Whole genome sequencing (WGS) analysis was also conducted to identify single nucleotide polymorphism (SNPs) and screened out two genetic mutations (lptD and rpsJ). The acrB gene of TR16 was knocked out through CRISPR/Cas9 system to further elucidate underlying mechanisms of tigecycline resistance in Salmonella Typhimurium. The up-regulation of acrB in TR16 was verified by RNA-seq and RT-qPCR, and the lack of acrB resulted in a 16-fold reduction in tigecycline resistance in TR16. Collectively, these results implied that AcrB efflux pump plays a key role in the tigecycline resistance of Salmonella, shedding light on the potential of AcrB efflux pump as a novel target for the discovery and development of new antibiotics.

Tetracyclic indole alkaloids with antinematode activity from Uncaria rhynchophylla.

A new tetracyclic indole alkaloid, 17-O-methyl-3,4,5,6-tetradehydrogeissoschizine, together with seven known ones, were isolated from the aerial part of Uncaria rhynchophylla. Their structures were unambiguously elucidated by spectroscopic methods and comparing with the literature data. Among them, compounds 1, 3, 4 and 6-8 showed potent to moderate antinematode activities against Panagrellus redivevus at a concentration of 250 µg/mL.

Terpenoids and their anti-feedant activity from Cipadessa cinerascens.

Eight tetranortriterpenoids (1-8) and two sesquiterpenoids (9 and 10) including two new compounds, cineracipadesin G (1) and 1ß-hydroperoxy-6α-hydroxy-eudesm-4(15)-ene (9), were isolated from the EtOAc extract of branches of Cipadessa cinerascens. The structures of two new compounds were elucidated by 1D and 2D NMR and MS spectroscopic analyses. The anti-feedant activity of two tetranortriterpenoids (1 and 7) was tested and obvious anti-feedant effects were detected.

Effect of post-harvest heat treatment on proteome change of peach fruit during ripening.

The extracted proteins from the heat-treated peach fruit (dipped in hot water at 48°C for 10min and then stored at room temperature (20°C-25°C) for up to 6 days) were used for proteomic analysis in order to understand the response of post-harvest peach fruit to heat treatment during ripening stage at proteomic level. After two dimensional gels electrophoresis (2-DE) was conducted, more than 600 protein spots were detected. Among them, 35 differently expressed spots (P<0.05) were selected to be excised and analyzed using MALDI-TOF/TOF, and finally 30 protein spots were confidently identified according to NCBI database. The results demonstrated that among the thirty protein spots expressed particularly induced by heat treatment, 43% were related to stress response, 17% to cell structure, 13% to protein fate, 7% to glycolytic pathway, 3% to ripening and senescence and 17% to unclassified. All of them are involved in the regulation of peach fruit development and ripening. All these indicated that the self-defense capability of peach fruit was improved by heat treatment. The study will enable future detailed investigation of gene expression and function linked with peach fruit ripening.