| Although the current disinfection technologies can effectively control the microbial contamination of tap water,the stagnation of tap water in the distribution system will lead to microbial contamination,which is still a global problem threatening human health.In order to solve the problem of "the last mile" of water supply,we urgently need to develop new and effective antibacterial agents as an auxiliary of conventional disinfectants.In order to achieved this goal,this paper successfully prepared two cationic chitosan polymer antibacterial agents(QCC and PCC)through simple synthesis procedures,quantified the antibacterial activity with E.coli and S.aureus as pathogen models,systematically studied the effects of different environmental factors on the antibacterial effect of them,and clarified the antibacterial(?)anism through the changes of bacterial surface morphology and intracellular dissolution,and the antibacterial application of two antibacterial agents in stagnant tap water was systematically evaluated.In this paper,the antibacterial effects of QCC and PCC on E.coli and S.aureus were studied by plate colony counting method.The results showed the maximum removal efficiencies of E.coli and S.aureus by QCC and PCC could exceed 92%when the reaction time was 1 h.The removal efficienciy of S.aureus by PCC reached 99.9%.At the same time,QCC and PCC had no significant effect on the antibacterial activity of pathogenic bacteria in water within the fluctuation range of environmental conditions with pH of 6.5-8.5,temperature of 5-40℃ and organic matter concentration of 0-3.0 mg/L.More importantly,both antibacterial agents had excellent regeneration and antibacterial durability,which was of great significance for practical application.In addition,combined with contact angle and other characterizations and the adsorption experiments of bovine serum albumin,it was found that QCC and PCC had good antibiological contamination.This paper also applied QCC and PCC to stagnant tap water,and took the seriously polluted river water as the model.The results showed that QCC and PCC could deal with microorganisms in the actual water well,and PCC had better antibacterial effect.Finally,longan,a tropical fruit,was taken as an example to study the fresh-keeping effects of the two antibacterial agents,and the antibacterial properties of them were further investigated.The results showed that both antibacterial agents could effectively keep fresh,and PCC had more obvious effect.For the purpose of protecting human health,tap water has high requirements for the cytotoxicity of antibacterial agents,so it needs to have low cytotoxicity.In this paper,the effects of chitosan,QCC and PCC on the proliferation of mouse fibroblasts were compared by MTT method,and then the cytotoxicity of the three materials was investigated.The results showed that both QCC and PCC could meet the requirements of toxicity level 1,and had very low cytotoxicity at the lowest effective concentration,which verified the applicability of the prepared functional materials.In this paper,the morphological changes of bacterias were observed by scanning electron microscope,the absolute number of dead and living bacterias before and after treatment was observed by dead and living cell staining method,and the changes of cell membrane permeability were revealed by ICP detection of intracellular K+ and soluble protein overflow,so as to speculate the potential mechanism of QCC and PCC antibacterial behavior:antibacterial agents adsorbed bacteria through electrostatic action and then destroyed their cell membranes,causing them to die.In conclusion,QCC and PCC have efficient and long-term antibacterial properties against stagnant tap water without cytotoxicity.They are expected to become antibacterial agents to ensure the biosafety of tap water. |
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