Search

Through our previous study, we found an up-regulation in the expression of nitrite reductase (nirS) in the isothiazolone-resistant strain of Pseudomonas aeruginosa. However, the definitive molecular role of nirS in ascribing the resistance remained elusive. In the present study, the nirS gene was deleted from the chromosome of P. aeruginosa ATCC 9027 and the resulting phenotypic changes of ΔnirS were studied alongside the wild-type (WT) strain under aerobic conditions. The results demonstrated a decline in the formations of biofilms but not planktonic growth by ΔnirS as compared to WT, especially in the presence of benzisothiazolinone (BIT). Meanwhile, the deletion of nirS impaired swimming motility of P. aeruginosa under the stress of BIT. To assess the influence of nirS on the transcriptome of P. aeruginosa, RNA-seq experiments comparing the ΔnirS with WT were also performed. A total of 694 genes were found to be differentially expressed in ΔnirS, of which 192 were up-regulated, while 502 were down-regulated. In addition, these differently expressed genes were noted to significantly enrich the carbon metabolism along with glyoxylate and dicarboxylate metabolisms. Meanwhile, results from RT-PCR suggested the contribution of mexEF-oprN to the development of BIT resistance by ΔnirS. Further, c-di-GMP was less in ΔnirS than in WT, as revealed by HPLC. Taken together, our results confirm that nirS of P. aeruginosa ATCC 9027 plays a role in BIT resistance along with biofilm formation and further affects several metabolic patterns under aerobic conditions.

This study investigated the effects of mold susceptibility, total soluble sugar contents and chemical components of wood fibers on mold resistance of wood-polypropylene composites (WPC) filled with white poplar, moso-bamboo, Chinese fir, Ramin, white pine, red gum, red cedar, and rubberwood. Susceptibilities and resistances to molds were studied by artificially accelerated tests. The total soluble sugar contents and chemical components of wood fibers were analyzed by anthrone colorimetry and gas chromatography-mass spectrometry (GC-MS), respectively. Experimental results showed that the mold resistance of WPC varied significantly with wood fiber species. Higher natural durability of wood fiber resulted in higher mold resistance of WPC, while higher sugar contents decreased the resistance of WPC against molds. Low initial moisture content did not have any influence on the susceptibility of WPC towards fungal attack, but higher final moisture content was the result of heavy mold growth on WPC. GC-MS analysis suggested that different chemical components of wood fiber species affected the mold resistance of WPC either positively or negatively. This study provides an alternative solution to improve the durability of WPC against fungal attack.

Inspired by antimicrobial peptides (AMP) which could alleviate drug resistance pressure, antimicrobial peptide mimics (AMPMs) were designed timely. Here, carboxymethyl cellulose (CMC) -based AMPMs were constructed by introducing different diamines on CMC effectively. Firstly, CMC was degraded to be oligomers with different molecular weights, followed by amination reactions with different diamines respectively. After protonation, a series of AMPMs with different structures were synthesized successfully. Their antibacterial effect has been evaluated by dynamic growth curves and microdilution method. The images snapped by the confocal laser scanning microscope and transmission electron microscope have fully proved its great lethality. And the antibacterial mechanism measured by flow cytometry analysis and zeta potential detection demonstrated that the destruction of membrane potential leads to bacteria death. The excellent blood compatibility and negligible drug resistance has also been confirmed. In addition, the synthesis method is simple and environmental-friendly.

Antibiotic pollution has been a serious global public health concern in recent years, photodynamic inactivation is one of the most promising and innovative methods for antibacterial applications that avoids antibiotic abuse and minimizes risks of antibiotic resistance. However, limited by the weak interaction between the photosensitizers and Gram-negative bacteria, the effect of photodynamic inactivation cannot be fully exerted. Herein, photosensitizer chlorin e6-loaded polyethyleneimine-based micelle was constructed. The synergy of electrostatic and hydrophobic interactions between the nanoparticles and the bacterial surface promoted the anchoring of nanoparticles onto the bacteria, resulting in enhanced photoinactivation activities on Gram-negative bacteria. As expected, an eminent antibacterial effect was also observed on the Gram-positive bacteria Staphylococcus aureus. The cellular uptake results showed that photosensitizer was firmly anchored to the bacterial cell surface of Escherichia coli or Staphylococcus aureus by the introduction of branched polyethylenimine-containing nanoparticles. The light-triggered generation of reactive oxygen species, mainly singlet oxygen, from the membrane-bound nanoparticles caused irreversible damage to the bacterial outer membrane, achieving enhanced bactericidal efficiency than free photosensitizer. The study would provide an efficient and promising antimicrobial alternative to prevent overuse of antibiotics and have enormous potential for human healthcare and the environment remediation.

Zwitterionic monomer methyacryloxyethyl sulfobetaine (MAES) copolymerized with hydroxyethyl methacrylate (HEMA) forming random copolymer with some block characteristics in a controlled manner. The polyzwitterionic copolymer P(MAESx-ran-HEMAy) (PMxHy, where x and y were the degrees of polymerization of MAES and HEMA, respectively), which bearing hydroxyl groups that served as both reducing and capping reagent for in situ AgNPs synthesis without exogenous additions. The in situ formed uniform AgNPs composites adopted a typical “core-shell” structure where AgNPs served as cores, and PMH were shells. The stability of the AgNPs composites was promoted by chelation of AgNPs core and the generated aldehyde on PMH during silver ions (Ag+ ions) reduction. Size of the AgNPs composites directly correlated with [MAES] to [HEMA] ratio in PMH and the highest yield of AgNPs composites was achieved when PM20H27 to AgNO3 weight ratio equaled 30%. The AgNPs composites originating from PM50H26 showed the most potent bactericidal activity through the membrane perturbation mechanism. Besides, the AgNPs composites confirmed safe for mammalian cells by hemolysis and cytotoxicity tests.

The effect of plating temperatures between 60 and 90°C on structure and corrosion resistance for electroless NiWP coatings on AZ91D magnesium alloy substrate was investigated. Results show that temperature has a significant influence on the surface morphology and corrosion resistance of the NiWP alloy coating. An increase in temperature will lead to an increase in coating thickness and form a more uniform and dense NiWP coatings. Moreover, cracks were observed by SEM in coating surface and interface at the plating temperature of 90°C. Coating corrosion resistance is highly dependent on temperature according to polarization curves. The optimum temperature is found to be 80 ∘ C and the possible reasons of corrosion resistance for NiWP coating have been discussed.

Farnesol, a 15-carbon, naturally occurring sesquiterpene alcohol, exists widely in plants and Candida albicans. It inhibits the production of the Pseudomonas Quinolone Signal (PQS) and pyocyanin of the opportunistic pathogen Pseudomonas aeruginosa, but the underlying mechanisms remained unknown. In this study, the actions of farnesol on the growth, production of virulence factors (including PQS signals, elastase, pyocyanin, biofilm, and swarming motility), and the transcription of some essential key genes of three Quorum Sensing (QS) systems and other related virulence genes in the P. aeruginosa PAO1 strain were investigated. Moreover, the qRT-PCR and high throughput transcriptome/proteome sequencing techniques were used to differentiate the transcriptomic/proteomic expressions of the PAO1 strain following farnesol exposure. The experimental results showed that farnesol did not inhibit PAO1 growth or affect its elastase production. However, farnesol did suppress the transcription and protein expression of the pqsABCDE and pqsH genes in the strain's pqs QS system and then inhibit the PQS production, while leaving the transcription and protein expression of pqsR in the pqs system, of lasI and lasR in the las QS system, and of rhlI and rhlR in the rhl QS system unaffected. Farnesol also inhibited the expression of some related virulence genes and the production of the related virulence factors. For example, it inhibited the protein expression of key genes in the phenazine biosynthesis pathway, including key genes related to pyocyanin synthesis (phzM, phzS), inhibiting the strain's capacity for biofilm formation. In addition, farnesol enhanced the transcription and protein expression of key genes in the geraniol degradation pathway. Farnesol also stimulated the PAO1 strain with regard to swarming motility. As a result, we concluded that farnesol can suppress the virulence by inactivating the pqs QS system in pathogen P. aeruginosa, which would be significant to develop a kind of effective drug control the virulence and pathogenesis of this bacteria.