Distribution And Spread Of Airborne Antibiotic Resistance Genes In The Environment Of Livestock Feedlots

Antibiotic resistance genes(ARGs)have been detected in various atmospheric environments.Airborne ARG transmission presents apublic health threat.However,it is very difficult to quantify airborne ARGs because of the limited availability of collectable airborne particulate matter and the low biological content of samples.Although livestock farms are hotspots of antibiotic resistance due to the intensive use of antibiotics,little is known about the abundance,diversity and transmission of airborne ARGs.There has been a knowledge gap about the profiles of airborne mobile genetic elements(MGEs),ARGs,and bacterial communities in no and in-feed antibiotics drugs.No systematic study investigated how different factors(such as temperature and the addition of antibiotics in feed)influence the horizontal gene transfer(HGT)of ARGs air and feces.More efforts are needed to prevent and control the potential health risks induced by airborne ARGs.An optimized protocol for collecting and detecting airborne ARGs is presented in this thesis.Experimental results showed that recovery efficiency tended to increase initially and then declined over time,and a range of 550–780 copies/mm~2 of capture loading was recommended to ensure that the recovery efficiency is greater than 75%.The highest concentrations of airborne ARGs were detected with 1.4μL/mm~2 buffer wash.Furthermore,the majority of the cells were disrupted by an ultrasonication pretreatment(5 min),allowing the efficiency ARGs detection of airborne samples.Extending the ultrasonication can disrupt cell structures and gene sequence was broken down into fragments.Therefore,this study provides a theoretical basis for the efficient filter collection of airborne ARGs in different environments.An optimized sampling method was proposed that the buffer wash was 1.4μL/mm~2 and the ultrasonication duration was 5 min.The bioaerosol is an important spread route of ARGs in pig farms.ARGs,MGEs,and bacterial communities were investigated in both air and feces samples during winter and summer.The average concentration of airborne ARGs and MGEs during winter is higher than that during summer when using the ventilation system in pig farm.The tet M is identified as the predominant airborne ARG with abundance of6.3±1.2 log copies/m~3.Clostridium and Streptococcus are two dominant bacteria and several opportunistic pathogens are detected in air samples of the pig farm.High temperature is favorable for more diverse bacterial communities,but relative humidity has negative effects.The wind speed promotes the spread of airborne ARGs.The network analysis results show the average fecal contribution to airborne bacteria is19.9%and 59.4%during summer and winter,respectively.In the pig farm,HGT plays an important role in the dissemination of airborne ARGs during winter(77.8%possibility),while a lower possibility of 12.0%in summer.In the chicken farm,ARGs/MGEs and bacterial communities in feces and air samples were quantified in summer and winter.The concentration of almost airborne ARG/MGE subtypes in winter is three or four orders of magnitude higher than those during summer in the chicken farm.The tet M is identified as the predominant airborne ARG with abundance of 7.9±1.3 log copies/m~3.The indoor air of chicken farms is a reservoir of ARGs in the environment.The antibiotic target protection was the dominant resistance mechanism of ARGs in all samples of this chicken farm.In feces samples,bacteria during winter might be easily distributed to the air in the intensive chicken farms.HGT would have become a major transmission route in the atmosphere of the chicken farm during winter.These results may contribute to a better understanding of the airborne ARGs transmission and distribution characteristics and provide a reference for assessing the risks arising from the chicken farm.The dynamics of various antibiotics were compared between feces samples from chicken fed a diet containing these antibiotics and no these drugs.The ecological risks of antibiotics in chicken feces with in-feed antibiotic drugs were higher than that with no drugs using the hazard quotient(HQ).Meanwhile,the concentration of almost all airborne ARG/MGE subtypes with in-feed antibiotic drugs is about two orders of magnitude higher than those with no drugs.Indoor air of chicken farms with in-feed antibiotics is a reservoir of ARGs in the environment.The continuous feeding of antibiotics drugs can increase the gut microbial community structure of the chicken.The possibility of horizontal gene transfer of ARGs in air and feces samples might be increased by in-feed antibiotic drugs.It is possible to reduce enrichment of ARGs in the surrounding environment of the chicken farm through minimizing antibiotic drugs use.The impaction of environmental factors(such as temperature)and different recipient bacteria on horizontal gene transfer of ARGs was investigated.When the recipient was Acinetobacter oryzae(Gram-negative bacteria),the concentration of survival resistant bacteria showed an obvious upward trend with the temperature increases.The highest concentrations of survival resistant bacteria were indicated when the recipient was Acinetobacter oryzae,which means the possibility of horizontal gene transfer was higher.This dissertation also found that Acinetobacter was the possible host of ARGs in the livestock farms.The difference in cell wall determines the different sensitivity of the two types of bacteria to different antibiotics.