Research On Distribution Of Antibiotic Resistance Genes In Vegetable Soils In Beijing

At present, antibiotics have been extensively used in medical industry and animal husbandry,resulting in the emerging of the diversity of resistant bacteria, the ARGs and even the multiple antibiotic resistant superbugs, which poses a gigantic threat to human health and environment.Therefore, the research of ARGs has attracted more and more attention in the field of environmental science. Farmland soil is an important repository and a medium for the spread of resistant bacteria and ARGs. This paper selected the vegetable base for a long term application of organic fertilizer in Beijing, to analyze resistant bacteria and ARGs in soil, revealing the effect of organic fertilizer on resistant bacteria and ARGs and the correlation between ARGs and residues of antibiotics and heavy metal in soil. This paper is of great significance for the control of pollution status and distribution characteristics of resistant bacteria and ARGs in farmland soil in Beijing, as well as the evaluation of the safety of the organic fertilizer application, and the reduction of the spread of resistant bacteria and ARGs.Greenhouse soil and field soil in 11 long-term organic vegetable bases in Beijing were collected for test. The soil was detected of 13 kinds of antibiotics, and the detection rate of SAs and TCs is 100% both in the field soil and the greenhouse soil. The detection rate of TCs was the highest among all the antibiotics, which was 73.65 μg/kg and 103.58 μg/kg in the field soil and the greenhouse soil, respectively. In addition, the six main heavy matals in the soil were detected in this paper, finding that the concentration of heavy metals in soil and organic manure were all Zn>Cr>Cu>Pb>As>Cd. The concentration of Zn, Cr and Cu in fecal samples were the highest,which were 246.44 mg/kg, 57.91 mg/kg and 38.85 mg/kg, respectively.The antibiotic resistant bacteria and 18 kinds of resistance genes in the soil were detected and analyzed. According to the testing results of ARGs with high detection rate, Class I integron intI1, sulfa resistance gene sul2, tetracycline resistance genes tetL and tetX were selected for fluorescence quantitative detection. The results showed that the tetracycline resistant bacteria accounted for the total number of bacteria in field soil was 1.91%, which was significantly lower than that in greenhouse soil(6.64%, P< 0.05). However, the ampicillin, sulfamethoxazole and ciprofloxacin resistant bacteria accounted for the total number of bacteria in the field and greenhouse soil were of no significant difference(P> 0.05). In the field and greenhouse soil, the detection rate of sulfa resistance genes sul I and sul2 were 100%. For other ARGs, the detection rate in greenhouse soil was higher than that in the field soil. According to the relative abundance of ARGs, the relative concentration of tetX and class I integron intI1 in greenhouse soil were significantly higher than that in field soil(P< 0.05), moreover, the relative concentration of tetLin greenhouse soil was extremely higher than that in field soil(P< 0.01). Thus, the pollution of ARGs in greenhouse soil was more serious than that in field soil, which may be related to the use of organic fertilizer in greenhouse soil with a larger amount.The correlation among antibiotics, heavy metal, ARGs and class I integron to anlysis. We found that the relative concentration of sul2 and tetX were significantly correlated with the concentration of some families of antibiotics and non cognate antibiotic concentration. There were significant correlations between heavy metals Zn and Cu with ARGs, but weak correlations for other heavy metals. Because the antibiotics and heavy metals in the environment have co-selection for the total abundance of ARGs. Visible, antibiotic and heavy metals are important factors of the increase of ARGs abundance in soil.In order to further study the effect of organic manure application on antibiotic resistant bacteria and ARGs in vegetable soil, four greenhouse soil with four different fertilization modes(no fertilization, conventional fertilization, single application of fertilizer and single application of organic fertilizer) were repeatedly sampled to research, founding that the antibiotic resistant bacteria and antibiotic resistant bacteria accounted for the total number of bacteria in the organic fertilizer soil(conventional fertilization soil and single application of organic fertilizer soil) were overall higher than that in the no fertilization soil and single application of chemical fertilizer soil 1 ~ 2 orders of magnitude, similarly, the absolute abundance and relative abundance of ARGs. It is further proved that organic manure could increase soil antibiotic resistance.