Rosemary and Tea Tree Essential Oils Exert Antibiofilm Activities In Vitro against Staphylococcus aureus and Escherichia coli.

ABSTRACT: The purpose of the present study was to determine the bioactive compounds in rosemary essential oil (REO) and tea tree essential oil (TEO) and to investigate their antibacterial and antibiofilm activities against Staphylococcus aureus and Escherichia coli in vitro. The MIC and MBC assays were performed to assess the antibacterial activity of these two EOs against S. aureus and E. coli with the broth microdilution method. A crystal violet assay was used to ascertain the effects of EOs on the biofilm formation of the test strains, and a tetrazolium bromide (MTT) assay was used to measure the level of inactivation of mature biofilms by EOs. Gas chromatography-mass spectrometry revealed 15 compounds in REO and 27 compounds in TEO, representing 97.78 and 98.13% of the total EO, respectively. Eucalyptol and α-pinene were found in high concentrations in REO, and the two major compounds in TEO were 4-terpineol and terpinolene. The MICs of REO for the two S. aureus and E. coli test strains were both 0.5 mg/mL, and the MICs of TEO for the two strains were both 0.25 mg/mL. Therefore, these EOs can significantly inhibit the formation of biofilms and induced morphological biofilm changes, as verified by scanning electron microscopy. Both EOs had destructive effects on the mature biofilm of the two test strains. TEO was more inhibitory than REO for biofilm formation by the two test strains.

Design and Synthesis of Cobalt-Based Electrocatalysts for Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) is the crucial step of various renewable energy conversion and storage technologies such as fuel cells and air-batteries. Cobalt-based electrocatalysts including oxides/chalcogenides and Co-Nx /C, one kind of non-precious metal electrocatalysts with competitive activity, enhanced durability, and acceptable cost, have been proposed as the potentially interesting alternatives to Pt-based electrocatalysts. In this account, we summarized the synthesis methods and the corresponding main impact factors including ligand effect, particle size effect, crystal structure, nanostructure, defects and active centers related to the ORR performance on both of oxides/chalcogenides and Co-Nx /C. Some special points have been discussed on design and synthesis of low-cost and high-performance cobalt-based electrocatalysts with enhanced electrocatalytic activity. Also, the current challenges and future trends are proposed for improving the performance of Co-involving electrocatalysts.