| Antibiotics are widely used to protect the health of human and animals or to increase growth rate of animals as food additive. The majority of antibiotics are excreted unchanged into the environment, then caused the chemical pollution by antibiotics themselves. The use of antibiotics may also aacelerate the development of antibiotic resistance genes (ARGs) and bacteria, which shade health risks to humans and animals. Animal manures handled with simple compost and oven dry methods are often used as green organic fertilizers to improve the soil quality, increase crop yield and quality. Due to the current standard about organic fertilizers does not include the forced antibiotic residues examination, the concerns of antibiotic residues in organic fertilizers are still unclear. When antibiotics and antibiotic resistance genes contained in organic fertilizers released to the soil environment, the new environmental pollution may be produced. In addition, some recent literatures reported that plant endophytic bacteria had multiple antibiotic resistances (MAR); however the source of MAR and its formation mechanism are still unclear. In this paper, the commercial organic fertilizers purchased from Nanjing city, China were examined its antibiotics residues by UPLC-MS/MS method and its antibiotic resistance genes by polymerase chain reaction (PCR) method. Furthermore, antibiotics enrofloxacin was added into soils, then the residues of enrofloxacin and in soil and Lactuca sativa as well as the antibiotic resistance genes qnrA and qnrB in soil and the endophytic bacteria in Lactuca sativa were detected. Meanwhile the abundances of qnrA and qnrB in soil and the endophytic bacteria from Lactuca sativa were examined and the correlations between the abundances of soil and endophytic bacteria from Lactuca sativa were analyzed. Our present works will help to explore the migration and variation of antibiotics and its antibiotic resistance genes in the environment, especially in the food chain.Eighteen veterinary antibiotic residues and related antibiotic resistance genes in eight kinds of commercial organic fertilizers purchase from Nanjing city. Except the sulfonamides, chlortetracycline and tyloosin, other nine antibiotics have been detected in the samples. Enrofloxacin, tetracycline and roxithromycin were detected in all eight organic fertilizers, the detection concentrations were from 24.3 to 225.5 μg·kg-1,13.9 to 92.4 μg·kg-1 and 13.6 to 32.6 μg·kg-1, respectively. The detection rate of ciprofloxacin and ofloxacin were 75%, the detection concentrations were varied from 33.6 to 141.0 μg·kg-1,12.9 to 360.6 μg·kg-1, respectively. The detection rate of norfloxacin, oxytetracycline, doxycycline and erythromycin were 62.5%,50%,37.5%, 25%, the detection concentrations were from 12.2 to 111.9 μg·kg-1,24.2 to 231.6 μg·kg-1,21.4 to 403.2 μg·kg-1 and 8.9 to 33.4 μg·kg-1, respectively. In the antibiotic resistance genes detection, nine antibiotic resistance genes were detected except tetT. Aac (6’)-Ib and tetW were detected in all kinds of organic fertilizers, qnrA, qnrB and letO also have a high detection rate. The above results indicated that the measured organic fertilizers contained a large number of veterinary antibiotic residues and the fluoroquinobnes and tetracyclines antibiotic resistance genes are also abundant. ARGs are considered to be a class of environmental contaminants at home and abroad today. With the application of organic fertilizers in the agriculture, secondary pollution of antibiotics may be produced, then affecting the food chain system.Different concentration of enrofloxacin were applied into soil, then the enrofloxacin residues in soil and its planting Lactuca sativa were examined, meanwhile, the abundances of qnrA and qnrB, two antibiotic resistance genes of fluoroquinolones, were examined in soil and the endophytic bacteria from Lactuca sativa were further compared. The results showed that enrofloxacin and its metabolite ciprofloxacin were detected in the leaf of Lactuca sativa and the amount was about 0.6% of the initial amount applied in soil. The qnr Aand qnrB were also detected in the endophytic bacteria from the leaves of Lactuca sativa and soil, the abundances of gnrAand qnrB were 1.54 to 3.25 times higher in the soil and leaves of Lactuca sativa with applied enrofloxacin in soils than that without enrofloxacin application respectively. The present studies demonstrated that the applied antibiotics in soil could induce the abundance of antibiotic resistance genes in plant via the endophytic bacteria.The author also isolated and identified the endophytic bacteria in leaves of Lactuca saliva. A total of 31 strains were isolated. Among them,22 strains (71% of total bacteria) were gram positive, which belong to 11 genera such as Bacillus, Paenibacillus Microbacterium and Arthrobacter. The number of isolated Bacillus was 10 (32.1% of total strains). The antibiotic susceptibility test showed that six bacteria strains belonging to Pseudomonas, Arthrobacter and Microbacterium respectively exhibited resistance to fluoroquinolone drugs and the congeneric strains showed the similar level of resistance. |
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