Mechanism Of Antimicrobial Activity Of Fluoroquinolones Sensitized By Mannuronic Acid Oligosaccharide

The abuse of antimicrobial drugs has increased the drug resistance rate of pathogenic bacteria year by year,and the infection of drug-resistant bacteria is a serious threat to human health.But the pace of research and development of new antimicrobial drugs lags far behind the evolution and spread of drug-resistant bacteria.With the development of antibacterial research,it has been found that constructing a combination drug strategy and restoring the sensitivity of drug-resistant bacteria to existing antibacterial drugs is an effective way to treat drug-resistant bacteria infections.Alginate oligosaccharide（AOS）is a mixed oligosaccharide obtained by controlling the degradation of alginate,including mannuronic acid oligosaccharide（MOS）,guluronic acid oligosaccharide（GOS）and hybrid oligosaccharides of the two.Previous studies have shown that the combination of MOS and antibacterial agents has a clear sensitizing antibacterial effect in inhibiting E.coli,but so far,the antibacterial mechanism of MOS sensitizing antibacterial agents is not clear.This study intends to explore the mechanism of MOS sensitizing antibacterial agents.This can not only lay the foundation for the development of related preparations and the formulation of medication plans,but also prolong the effective service life of existing antibacterial drugs and slow down the urgency of new drug development.Chapter 1:Introduction.The preparation,purification and biological activity of MOS were reviewed,and the research progress of MOS in antibacterial application was summarized.Chapter 2:Preparation and purification of MOS.The MOS was prepared by acid degradation.The MOS was purified by dextran gel chromatography and characterized by capillary zone electrophoresis（CZE）.It was determined that the composition of MOS had no change before and after purification,and the degree of polymerization of the sample was within the range of oligosaccharides.At the same time,in order to clarify the pharmacological effect of MOS,glucooligosaccharides with similar polymerization degree composition as MOS were prepared as the control,which were used in the subsequent experiments of E.coli inhibition by MOS sensitizing antibacterial agent.Chapter 3:MOS combined with fluoroquinolone antibacterial agents to inhibit the activity of E.coli.The activity experiment of MOS,oligoglucose combined with fluoroquinolone antibacterial agents ciprofloxacin（CPFX）and levofloxacin（LVFX）to inhibit common E.coli was carried out by the multiple dilution method.The results showed that when MOS is used in combination with CPFX and LVFX,high concentrations had antagonistic effects,and low concentrations produced sensitizing antibacterial effects,while oligoglucose did not have such pharmacological effects.Chapter 4:Determination of the concentration of fluoroquinolone antibacterial agents in E.coli.High performance liquid chromatography（HPLC）was used to investigate the concentration of CPFX and LVFX in E.coli when different concentrations of MOS were combined with CPFX and LVFX,and to explore the mechanism of MOS sensitizing CPFX and LVFX to inhibit the activity of E.coli.The results showed that the concentrations of CPFX and LVFX in E.coli were lower than those in the group without MOS when MOS was combined with two kinds of antibacterial agents.When low concentration MOS was combined with antimicrobial agents,the contents of CPFX and LVFX in E.coli were higher than those in the group without MOS.The results were verified by observing the fluorescence intensity of the antibacterial agent by confocal laser scanning microscopy（CLSM）,and the results were consistent with the trend of determination of CPFX and LVFX in E.coli by HPLC.Chapter 5:The effect of Ca²⁺on the increase of the content of fluoroquinolone antibacterial agents in E.coli by MOS.This chapter used the multiple dilution method to explore the effect of adding Ca²⁺to the culture medium on the inhibition of E.coli activity by MOS sensitizing CPFX and LVFX.The results showed that the addition of Ca²⁺ion reversed the antagonistic effect of high concentration MOS to some extent,and increased the concentrations of CPFX and LVFX in the bacteria.It was speculated that after MOS chelated with more Ca²⁺ions,positively charged Mo S-Ca²⁺acted with negatively charged cell membrane,which improved the permeability of cell membrane and made CPFX and LVFX easier to enter into the bacteria.Chapter 6:Conclusion and Prospect.