Pathogenic Bacteria In Atmospheric Particles In Xi’an City Distribution Characteristics And Health Risk Studies

Microorganisms in atmospheric particulate matter are closely related to material circulation,biological transmission and public health.Especially in the context of 2019-nCoV outbreak,the distribution characteristics,pathogenic mechanism and health risks of rich pathogenic biological components in atmospheric particulate matter have once again become a research hotspot.In this study,Xi’an,a typical city with serious particulate pollution in Northwest China,as the research area,we explored the spatial distribution and community characteristics of pathogenic microorganisms in atmospheric particulate matter(urban dust precipitation and road dust),analyzed the mechanism of action of virulence factors,and evaluated and predicted the health risks to human beings by using metagenomics and traditional plate separation techniques.The following conclusions were obtained:(1)Crowd gathering behavior affects the composition of microorganisms in the air and human health risks.The crowd gathering behavior will change the level of air microbial pollution from clean to medium pollution,and the types,colors,morphology,wetness and biochemical properties of the cultured microorganisms will have new changes.The number of airborne pathogenic microorganisms increased from 2 to 9,and 5 of them were zoonotic microorganisms with BSL-Ⅱ.high biological risk.Based on the HQ model,it was found that the health risk exposure coefficient faced by people during crowd gathering increased by 1.284.96 times compared with before crowd gathering,and the risk of infection in men was significantly higher than that in women.(2)The types of microorganisms in road dust are diverse,and the spatial distribution is not obvious.Gene annotation found that there were 15280923 microbial non-redundant genes,183 phylums and 3394 genera in road dust in Xi’an,with bacteria accounting for 85.6%,fungi accounting for 0.9%,viruses accounting for 0.1%,and other microorganisms accounting for 13.4%.The spatial distribution characteristics of microorganisms in road dust show the characteristics of "low center and high perimeter",which is speculated to be due to the strict cleaning and disinfection measures in the city center,so that microorganisms accumulate less on road dust.In addition,there was no statistically spatial difference in the alpha diversity of microorganisms in urban road dust(p=0.061),mainly because the external force(carrying and transfer of people and vehicles)and the type of urban land application were highly similar,resulting in microbial attachment and accumulation on road dust.(3)Road dust contains highly infectious and seriously disease-causing pathogenic microorganisms.There were 171 pathogenic microorganisms(52 BSL-Ⅱ and 10 BSL-Ⅲ),such as high-risk infectious pathogenic microorganisms such as Yersinia pestis,Brucella melitensis and Mycobacterium tuberculosis,and there was no significant spatial difference in the structure of pathogenic microbial communities between different urban functional areas,showing the ubiquitous presence and high circulation of pathogenic microorganisms in urban road dust.Combined with the combing of the abundance of virulence factors and the general pathogenic mechanism of pathogenic microorganisms,it is found that pathogenic microorganisms in road dust can complete the chain of events that invade the human body under the synergy of different virulence factors:Adherence-Biofilm formation-Toxin-Iron Acquisition-Immune evasion.Compared with other events,the potential probability of Toxin events caused by pathogenic microorganisms in road dust after invading the human body is low,while the probability of Immune evasion events is higher,which suggests that the pathogenic microorganisms in road dust have a strong ability to escape immune interference in the human body.Traceability analysis of urban facilities,soil contaminated by traffic and the human body itself may be the main sources of pathogenic microorganisms in road dust.(4)Based on the improved Wells-Riley health risk model and preconditions,the daily probability of lung disease caused by inhalation of pathogenic microorganisms in road dust in children,middle-aged and elderly groups was 3.5(?),6.2(?) and 4.8(?),respectively;the probability of intestinal disease was 1.5(?),2.7(?) and 2.0(?),respectively;the rate of skin diseases 0.03(?),0.06(?)and 0.05(?),respectively.Among them,the probability of lung disease caused by road dust in middle-aged people is similar to the actual respiratory system prevalence in urban areas,in addition,regular dust suppression work of road environment sprinkling can effectively reduce the risk of citizens being infected by pathogenic microorganisms.