As a new type of environmental pollutants, microplastics are widely distributed in the global ecosystem, and ingestion of microplastics may produce a number of toxic effects. Based on currently available publications, this paper describes the main pathways of exposure to microplastics, and summarizes the toxic mechanisms of microplastics in mammals, including oxidative stress, inflammatory response, immune damage, imbalance of gut microbiota, energy metabolism disorder and DNA damage, so as to provide insights into elucidation of the toxic mechanism mechanisms and health risk assessment of microplastics.

Objective To explore the effects of polystyrene microplastics(PS-MPs)on the growth,activity,oxida-tive stress levels,biofilm formation and virulence of Klebsiella pneumoniae.Methods Klebsiella pneumoniae was exposed to PS-MPs at different concentrations(10,50 and 100 μg/ml)and particle sizes(0.1,1.0 and 5.0 μm),and the growth curves were measured.The bacterial activity was determined by CCK-8(cell counting kit-8).The level of intracellular reactive oxygen species(ROS)was determined by fluorescence probe.The biofilm forming ability was determined by crystal violet staining.Real-time quantitative fluorescent PCR(qRT-PCR)was used to detect the relative expression levels of biofilm-forming genes(luxS,mrkA,wbbM,pgaA,wzm)and viru-lence genes(ureA,uge,wabG,fimH).Results A high concentration(100 μg/ml)of 0.1 μm PS-MPs had a stronger inhibitory effect on the growth and activity of Klebsiella pneumoniae,and the intracellular ROS level signifi-cantly increased,indicating that smaller particle size and higher concentration of PS-MPs were more toxic to bacte-ria.PS-MPs of 100 μg/ml particle size groups(0.1,1.0 and 5.0 μm)significantly promoted the biofilm forma-tion of Klebsiella pneumoniae.The relative expression levels of biofilm formation related genes(luxS,mrkA,wbbM,pgaA,wzm)and virulence genes(ureA,uge,wabG,fimH)increased.Conclusion By inducing Kleb-siella pneumoniae to produce a high level of ROS,PS-MPs can cause oxidative stress,inhibit the growth and activi-ty of bacteria,and enhance the biofilm formation ability and virulence,thus affecting the biological characteristics of Klebsiae pneumoniae.