Effect of Terminalia chebula Retz. extraction with water on Staphylococcus epidermidis activity and its biofilm formation

Background:Based on modern pharmacological studies,Terminalia chebula Retz.exhibits antimicrobial activity against a variety of bacteria.Previously,we found Terminalia chebula Retz.exhibited excellent antibacterial activity against Malassezia restricta.Methods:We determined the minimal inhibitory concentration(MIC)and minimum bactericidal concentration of Terminalia chebula Retz.extraction with water(TRW)against Staphylococcus epidermidis(including Staphylococcus epidermidis 1-15)using the microdilution method.Staphylococcus epidermidis 1(SE11),which was the most sensitive to TRW,was selected as the test bacterium for subsequent experiments.The time-kill curve of TRW on SE11 was generated using the viable count method.Further,an in vitro biofilm model of SE11 was constructed using the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-((phenylamino)carbonyl)-2H-tetrazolium hydroxide test,semi-quantitative crystal violet experiment,and scanning electron microscopy.The effects of TRW on the total amount of biofilm formation,the number of viable biofilm bacteria,and biofilm microstructure of SE11 were also determined using a semi-quantitative crystal violet experiment,viable count method,and scanning electron microscopy.Finally,the electrical conductivity and soluble protein content of the SE11 suspensions were determined.Results:The average MIC of TRW against SE11 was 0.75±1.09 mg/mL.TRW(1/2MIC and 2MIC)and zinc pyrithione(1/2MIC and 2MIC)had no significant effect on total biofilm inhibition in the adhesion stage(P>0.05)and the aggregation stage(P>0.05).Further,TRW(1/2MIC and MIC)and zinc pyrithione(1/2MIC and MIC)had no significant effect on viable biofilm bacteria in the adhesion stage(P>0.05)and aggregation stage(P>0.05).TRW destroyed the integrity of the SE11 cell membrane,resulting in leakage of intracellular substances.Conclusion:TRW inhibits SE11 biofilm formation and is similar to zinc pyrithione in the adhesion and aggregation stages,which provides a theoretical basis for its application in the field of antimicrobial additives.

Nonlocal Galerkin Strip Transfer Function Method for Vibration of Double-Layered Graphene Mass Sensor

Double-layered graphene sheets （DLGSs） can be applied to the development of a new generation of nanomechanical sensors due to their unique physical properties. A rectangular DLGS with a nanoparticle randomly located in the upper sheet is modeled as two nonlocal Kirchhoff plates connected by van der Waals forces. The Galerkin strip transfer function method which is a semi-analytical method is developed to compute the natural frequencies of the mass- plate vibrating system. It can give exact closed-form solutions along the longitudinal direction of the strip. The results obtained from the semi-analytical method are compared with the previous ones, and the differences between the single-layered graphene sheet （SLGS） and the DLGS mass sensors are also investigated. The results demonstrate the similarity of the in-phase mode between the SLGS and DLGS mass sensors. The sensitivity of the DLGS mass sensor can be increased by decreasing the nonlocal parameter, moving the attached nanoparticle closer to the DLGS center and making the DLGS smaller. These conclusions are helpful for the design and application of graphene-sheet-based resonators as nano-mass sensors.

Antifungal Activity of Aspidin BB from Dryopteris fragrans against Trichophyton rubrum Involved Inhibition of Ergosterol Biosynthesis

Objectives Aspidin BB, a typical phloroglucinol derivative from Dryopteris fragrans, possesses significant antifungal property. This study aimed to investigate potential mechanism of antifungal activity of Aspidin BB against Trichophyton rubrum which is the most common pathogens responsible for chronic dermatophytosis. Methods The minimum inhibitory concentration （MIC） ofAspidin BB against strains was determined by broth microdilution. The effects of Aspidin BB on ergosterol biosynthesis were investigated by content determination based on UPLC method. Besides, the effects of drugs on squalene epoxidase （SE） in T. rubrum cell membrane were analyzed. Results MIC value of Aspidin BB against T. rubrum was 25.0 IJg/mL. Aspidin BB reduced ergosterol content significantly, but no notable effect on squalene epoxidase activity. Conclusion The results suggested that Aspidin BB inhibited ergosterol biosynthesis. However, it was not squalene epoxidase but other components may sever as possible targets in ergosterol biosynthesis pathway.