| Currently,antibiotic resistance has forced many countries to reduce or even ban the use of antibiotics in feed.Therefore,the development of new antibiotic alternatives to control infectious diseases in aquaculture is urgent.Cationic antibacterial polymers have attracted extensive attention due to their unique physical membrane-breaking sterilization mechanism.However,the membrane-breaking bactericidal mechanism of cationic antibacterial polymers enables them to have a very low drug resistance development rate,and at the same time,they can also destroy eukaryotic cell membranes.To address the problem of eukaryotic cytotoxicity,researchers have explored a variety of strategies to reduce toxicity,including but not limited to changing the secondary spatial structure of polymers,introducing degradable groups and dual action mechanisms.Although these strategies can reduce the toxicity to eukaryotic cells to a certain extent,this still limits their clinical application.In this paper,a series of degradable oligoguanidines were designed and synthesized based on the multivalent small groove binding ability of biguanide derivatives to DNA and the stimuli-responsive characteristics of ketals and ketals.By screening the antibacterial activity and biocompatibility of degradable oligoguanidine,P2 A and P4B with the highest therapeutic index were obtained.The degradation kinetics of P2 A and P4B were further studied,and a more stable P4B was obtained.Mechanistic experiments proved that P4B was indeed sterilized by the dual action of physical membrane rupture and intracellular DNA binding.The membrane-breaking bactericidal mechanism of P4B enables it to act synergistically with antibiotics as a sensitizer against three model bacteria(Escherichia coli,Bacillus subtilis,and Mycobacterium smegmatis).Based on the dual mechanism of P4B membrane breaking and DNA binding,it is difficult for bacteria to develop resistance to P4B through simple mutation or modification.Furthermore,the degradation products of P4B did not possess antibacterial activity and cytotoxicity,indicating that this degradable property enhances the biocompatibility and environmental friendliness of this material.The efficacy of P4B in vivo was demonstrated by establishing a zebrafish wound model of Edwardsiella lentus infection.The experimental results show that P4B can improve the survival rate of zebrafish and promote wound healing without causing significant toxicity to zebrafish at therapeutic concentrations.This model successfully demonstrated the potential of P4B as an aquaculture disinfectant.The potential application of P4B in aquaculture was demonstrated by further studies on the antibacterial activity of P4B in real water samples and simulated pond environments(water and soil).The experimental results showed that the bactericidal ability of the low-concentration P4B stock solution gradually weakened with time;the P4B stock solution in the pond environment lost its activity to Edwardsiella lentus after 3 days,which may be related to the organic matter and silicic acid in the P4B and soil.adsorption of salt colloids.In conclusion,this novel degradable oligomeric material or its further improved analogs can be used as disinfectants and therapeutics in aquaculture. |
