Distribution Characteristics Of Antibiotic Resistance Genes In Feces Of Beef Cattle Farms

Antibiotic Resistance Genes(ARGs)are the source of bacterial resistance and can be transmitted horizontally and vertically,which is more harmful to the environment and human health than antibiotics themselves.The feces of livestock and poultry farms are repositories of ARGS,while there are few studies on its distribution characteristics and influencing factors of transfer and transmission.Therefore,in this study we investigated the breeding situation of beef cattle farms in Haiyuan County from Ningxia.The abundance of ARGs in beef cattle feces was detected by fluorescence quantitative PCR technology.Combined the correlation analysis of heavy metal content,nutrient concentration and microbial composition with ARGs abundance in feces,the key factors affecting the abundance and transmission of ARGs in beef cattle farms were explored.All these results will provide a scientific basis for controlling the pollution of ARGs in livestock and poultry farms,promoting the healthy breeding for beef cattle and reducing their public health risks.The findings are as follows:(1)The beef cattle farms surveyed raised Simmental cattle mostly by self-breeding and self-raising.It was different in the feeding and management methods among beef cattle farms,and it was higher in the mechanization level for many kinds of cattle farms with high stocks.Beef cattle farms with a stock of more than 100 head used many kinds of antibiotics,and of which β-lactam antibiotics was the most,followed by aminoglycosides.Feces of beef cattle farms with more than 100 head would be collected together for composting.Beef cattle farms with less than 100 head generally did not use antibiotics,and feces of these farms would be directly applied to farmland.Most cattle farms have a low frequency of cleaning feces and disinfection frequency was various.(2)Six categories including eleven ARGs(aadA,strA,strB,bla TEM,cml A1,flo R,erm B,sul2,tet O,tet W,tet X)and two mobile genetic elements(MGEs)(Int1,Tp614)were widely present in cattle farm feces,and the quinolone gene was not detected.The relative abundance of most ARGs and MGEs in feces of cattle farms with more than 300 heads,breeding cattles more than 1 year,using antibiotics in the breeding process or having a low frequency of cleaning feces was relatively higher.The relative abundance of some ARGs and MGEs(aadD,fex A,erm B,erm X,tet S,Tp614)in feces of cattle farms with a low frequency of disinfection was also relatively higher.ARGs and MGEs with high abundance have a potential risk of transmission.(3)There was a widespread co-occurrence in ARGs of cattle farm feces.Mobile genetic elements(Int1,Int2),Pb,and K are significantly positively correlated with multiple ARGs,and changes in Int1,Int2,Pb,K,and actinomycete phylum also caused changes in the resistant genome.The bifidobacterium genus,ornithine microbacterium,and corynebacterium genus may be important potential hosts for resistance genes.In summary,the breeding scale and feeding management mode of beef cattle farms would affect the enrichment and transmission of ARGs from beef cattle feces.About 78% of ARGs with high detection rate was co-occured.Genetic elements Int1 and Int2 mediated the transfer and spread of ARGs between microorganisms.Bifidobacterium species,ornithate microbacterium,and Corynebacterium are important potential host bacteria of ARGs.The coselection of Pb and K to ARGs makes them likely to become the driving factors of ARGs transmission,however,the specific driving mechanism needs to be further studied.It is suggested that using antibiotics decreasedly or not use antibiotics in the beef cattle breeding process,appropriately increasing the frequency of cleaning feces and improving the standardization and effectiveness of disinfection will be helpful to control the enrichment and spread of ARGs.