Prevalence And Dissemination Of Antibiotic Resistance Genes In Chinese Dairy Farms And Fecal Bacteria In Yaks (Bos Grunniens) On The Qinghai-Tibet Plateau

Around the world,the prevalence of antibiotic resistance genes(ARGs)pose a significant risk to human and animal health.The accumulation and evolution of ARGs were promoted by the strong selection pressure caused by over use of antibiotics in animal industry.There are few comprehensive information about the prevalence of ARGs in dairy feces and the adjacent environment in China.Firstly,we investigated the use of antibiotics and collected fecal and soil samples in dairy farms in Shanxi Province.Abundance and diversity of ARGs in the feces and soil samples obtained from the dairy farms were evaluated using high-throughput metagenomic sequencing approach.A variety of ARGs have been detected conferring resistance to most classes of antibiotics,such as ?-lactam,tetracycline,macrolide,aminoglycoside,sulfonamides,chloramphenicol,streptogramin,and polypeptide antibiotics.The number of ARGs observed between the feces and soil samples were significantly correlated(R2 = 0.66,p<0.01).In addition,heavy metals(copper and zinc)have been detected in the fecal and soil samples.In the fecal samples,the concentrations of copper and zinc were 9.80-52.93 mg/kg and 30.75-179.7 mg/kg,respectively.In the soil samples,the concentrations of copper and zinc were 18.77-58.88 mg/kg and 55.06-146.8 mg/kg,respectively.There is significant correlation between the concentrations of heavy metal and the abundance of metal resistance genes(MRGs;R2 = 0.48,p<0.01).In the fecal samples,the number of ARGs was positively related with heavy metals(R2 = 0.63,p<0.01)and MRGs(R2 = 0.95,p<0.001).The number of ARGs detected was significantly correlated with MRGs in the soil(R2 = 0.81,p<0.001).The abundance of mobile genetics elements,such as transposase,were also examined to evaluate the potential risk of horizontal ARGs transfer.The positive correlation(R2= 0.77,p<0.001)between transposase genes and ARGs abundance.A positive correlation was shown between the ARGs abundance and the number of dairy cows(R2 = 0.41,p<0.01).After that,fecal samples of adult dairy cattle,manure samples,and fecal samples of calves were collected in Shandong,Henan,Hebei,Jiangsu,Inner Mongolia,Xinjiang,and Shanxi Province.In total,12 ARGs and 9 transposase genes were detected using qPCR.The results showed that high abundance of ARGs and transposase genes existed in all samples.Mean abundance of ARGs of manure samples was 2.6 times more than those in fecal samples of adult dairy cattle.Meanwhile,the abundance of ARGs of fecal samples of calves was 7.6 times more than those in fecal samples of adult dairy cattle.There was a positive correlation of abundance between ARGs and transposase genes(R2= 0.91,p<0.001).Gut microbial diversity and ARGs abundance of farm animal have been widely studied.The gut microbial diversity and ARGs abundance in yaks(Bos grunniens)on the Qinghai-Tibet Plateau is still unknown.Hence,we collected the fecal samples of yaks on the Qinghai-Tibet Plateau to evaluate gut microbial diversity and ARGs abundance.The data of 16S rRNA sequencing showed that Firmicutes(53.7%),Bacteroidetes(33.5%),and Proteobacteria(4.7%)were the predominant bacterial phyla.The ratio of Firmicutes to Bacteroidetes was as high as 1.60 among the yaks.The genera Clostridium,Bacteroides,Prevotella,and Akkermansia were found to be abundant in all the fecal samples and may play important roles such as provision of short chain fatty acids to the host,stimulation of probiotic bacteria,and maintenance of the microbial balance in the gut of yaks.In addition,a total of 10 ARGs were detected in all the samples with high levels of relative abundance;these ARGs confer resistance to tetracycline,sulfonamide,macrolide,streptomycin,and chloramphenicol.