Mechanism Of Natural Products Affecting Bacterial Resistance Transfer And Its Synergistic With Chlorination

The emergence and spread of antibiotic resistance pose a serious threat to public health and the environment,undermining decades of human progress in fighting pathogenic bacterial infections.Lacking of novel and effective antimicrobial approaches and the rapid spread of antibiotic resistance genes in the ecosystem make the problem of resistance difficult to manage.As emerging contaminants,the widespread spread of antibiotic resistance bacteria and antibiotic resistance genes in water treatment systems makes drug resistance a threat to human life and public safety,and there is no specific treatment process in existing water treatment systems.Disinfection process is a vital step that has the potential to control bacterial resistance,however its removal and control of the more resistant microorganisms is limited,leaving the risk of residual resistance in water still.Interspecies transfer occurring with plasmids as carriers is often considered to be the main way in which antibiotic resistance genes are spread in the environment;therefore,research and development of strategies to inhibit plasmid conjugation transfer is an important step in controlling the spread of resistance.In this thesis,we investigated the effect of cinnamaldehyde on the conjugate transfer of antibiotic resistance genes and the quorum-sensing system of antibiotic resistance bacteria,and explored the effect and mechanism of its combination with chlorine disinfection on the control of antibiotic resistance bacteria,the main contents and conclusions are as follows.(1)Interspecies bacterial antibiotic resistance gene conjugation transfer.Cinnamaldehyde inhibited the interspecies transfer of antibiotic resistance genes in E.coli DH5a and PAOI conjugation transfer system in both LB nutrient environment and PBS nutrient-free environment.100 mg/L cinnamaldehyde reduced the conjugation transfer frequency from 1.5×10-5 to 2.0×10-7 in LB and from 1.9×10-4 to 1.4×10-6 in PBS buffer.Meanwhile EPS changed in the conjugation transfer in the presence of cinnamaldehyde.(2)Quorum-sensing and virulence of natural resistance bacteria.The expression of genes related to the quorum-sensing of P,aeruginosa was inhibited by the presence of cinnamaldehyde,indicating that cinnamaldehyde can act as a quorum-sensing inhibitor.Cinnamaldehyde can inhibit the formation of biofilm and the secretion of rhamnolipid of P.aeruginosa.(3)Study of the effect of combination on the control of antibiotic resistant bacteria.As an antimicrobial agent,cinnamaldehyde can enhance the inactivation of chlorine disinfection on P.aeruginosa and synergistically increase the level of ROS and cell membrane permeability,thus causing damage to the bacteria.In addition,the removal of mature biofilm was significantly enhanced by the combination of cinnamaldehyde and chlorination.Therefore,cinnamaldehyde was able to synergize with chlorine disinfection to present a further removal effects on antibiotic resistance bacteria.