Antibiotics played an important role in controlling the development of enteric infection. However, the emergence of antibiotic resistance and gut dysbiosis led to a growing interest in the use of natural antimicrobial agents as alternatives for therapy and disinfection. Chitosan is a nontoxic natural antimicrobial polymer and is approved by GRAS (Generally Recognized as Safe by the United States Food and Drug Administration). Chitosan and chitosan derivatives can kill microbes by neutralizing negative charges on the microbial surface. Besides, chemical modifications give chitosan derivatives better water solubility and antimicrobial property. This review gives an overview of the preparation of chitosan, its derivatives, and the conjugates with other polymers and nanoparticles with better antimicrobial properties, explains the direct and indirect mechanisms of action of chitosan, and summarizes current treatment for enteric infections as well as the role of chitosan and chitosan derivatives in the antimicrobial agents in enteric infections. Finally, we suggested future directions for further research to improve the treatment of enteric infections and to develop more useful chitosan derivatives and conjugates.

Background: Uracil DNA glycosylases are DNA repair enzymes involved in the removal of base damage. Results: Family 5 UDGb is a uracil, hypoxanthine, and xanthine DNA glycosylase. Conclusion: Family 5 UDGb adapts multiple catalytic amino acids for the excision of pyrimidine and purine deaminated DNA bases. Significance: Family 5 UDGb exemplifies functional diversity in enzyme superfamilies.

A series of sulfonated poly(aryl ether ether ketone ketone)s statistical copolymers with high molecular weights were synthesized via an aromatic nucleophilic substitution polymerization. The sulfonation content (SC), defined as the number of sulfonic acid groups contained in an average repeat unit, could be controlled by the feed ratios of monomers. Flexible and strong membranes in sodium sulfonate form could be prepared by the solution casting method, and readily transformed to their proton forms by treating them in 2 N sulfuric acid. The polymers showed high T g s, which increased with an increase in SC. Membranes prepared from the present sulfonated poly(ether ether ketone ketone) copolymers containing the hexafluoroisopropylidene moiety (SPEEKK-6F) and copolymers containing the pendant 3,5-ditrifluoromethylphenyl moiety (SPEEKK-6FP) had lower water uptakes and lower swelling ratios in comparison with previously prepared copolymers containing 6F units. All of the polymers possessed proton conductivities higher than 1 Â 10 À2 S/cm at room temperature, and proton conductivity values of several polymers were comparable to that of Nafion at high relative humidity. Their thermal stability, oxidative stability, and mechanical properties were also evaluated.

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Operational support is a key issue for aircraft maintenance, which aims to improve operational efficiency and reduce operating costs under the premise of ensuring flight safety. Although many works have emerged to achieve this aim, they mostly address the concept of maintenance systems, the relationship between stakeholders and the loop of maintenance information separately. Hence, the cooperation between stakeholders could be impeded especially when urgent decisions should be made, relying on historical data and real-time data. In this