Update on molecular diversity and multipathogenicity of staphylococcal superantigen toxins

Staphylococcal superantigen(SAg)toxins are the most notable virulence factors associated with Staphylococcus aureus,which is a pathogen associated with serious community and hospital acquired infections in humans and various diseases in animals.Recently,SAg toxins have become a superfamily with 29 types,including staphylococcal enterotoxins(SEs)with emetic activity,SE-like toxins(SEIs)that do not induce emesis in primate models or have yet not been tested,and toxic shock syndrome toxin-1(TSST-1).SEs and SEIs can be subdivided into classical types(SEA to SEE)and novel types(SEG to SEIY,SE01,SE02,SEI26 and SEI27).The genes of SAg toxins are located in diverse accessory genetic elements and share certain structural and biological properties.SAg toxins are heat-stable proteins that exhibit pyrogenicity,superantigenicity and capacity to induce lethal hypersensitivity to endotoxin in humans and animals.They have multiple pathogenicities that can interfere with normal immune function of host,increase the chances of survival and transmission of pathogenic baaeria in host,consequently contribute to the occurrence and development of various infeaions,persistent infeaions or food poisoning.This review focuses on the following aspeas of SAg toxins:(1)superfamily members of classic and novelty discovered staphylococcal SAgs;⑵diversity of gene locations and molecular structural characteristics;(3)biological characteristics and activities;(4)multi-pathogenicity of SAgs in animal and human diseases,including bovine mastitis,swine sepsis,abscesses and skin edema in pig,arthritis and septicemia in poultry,and nosocomial infections and food-borne diseases in humans.

Using thermodynamic parameters to study self-healing and interface properties of crumb rubber modified asphalt based on molecular dynamics simulation

The thermodynamic property of asphalt binder is changed by the addition of crumb rubber,which in turn influences the self-healing property as well as the cohesion and adhesion within the asphalt-aggregate system.This study investigated the self-healing and interface properties of crumb rubber modified asphalt(CRMA)using thermodynamic parameters based on the molecular simulation approach.The molecular models of CRMA were built with representative structures of the virgin asphalt and the crumb rubber.The aggregate was represented by SiO2 and Al2O3 crystals.The selfhealing capability was evaluated with the thermodynamic parameter wetting time,work of cohesion and diffusivity.The interface properties were evaluated by characterizing the adhesion capability,the debonding potential and the moisture susceptibility of the asphalt-aggregate interface.The self-healing capability of CRMA is found to decrease as the rubber content increases.The asphalt-Al2O3 interface with higher rubber content has stronger adhesion and moisture stability.But the influence of crumb rubber on the interfacial properties of asphalt-SiO2 interface has no statistical significance.Comparing with the interfacial properties of the asphalt-SiO2 interface,the asphalt-Al2O3 interface is found to have a stronger adhesion but a worse moisture susceptibility for its enormous thermodynamic potential for water to displace the asphalt binder.

Effect of styrene-butadiene-styrene copolymer on the aging resistance of asphalt:An atomistic understanding from reactive molecular dynamics simulations

To reveal the potential influence of styrene-butadiene-styrene(SBS)polymer modification on the anti-aging performance of asphalt,and its mechanism,we explored the aging characteristics of base asphalt and SBS-modified asphalt by reaction force field(ReaxFF)and classical molecular dynamics simulations.The results illustrate that the SBS asphalt is more susceptible to oxidative aging than the base asphalt under oxygen-deficient conditions due to the presence of unsaturated C=C bonds in the SBS polymer.In the case of sufficient oxygen,the SBS polymer inhibits the oxidation of asphalt by restraining the diffusion of asphalt molecules.Compared with the base asphalt,the SBS asphalt exhibits a higher degree of oxidation at the early stage of pavement service and a lower degree of oxidation in the long run.In addition,SBS polymer degrades into small blocks during aging,thus counteracting the hardening of aged asphalt and partially restoring its low-temperature cracking resistance.