| In this dissertation, we studied antibiotic resistence strains and resistence genes in different soils. Information provided in this work may contribute to a better understanding antibiotic resistance in soil environment, which will be useful reference for reasonable antibiotic application. Main results obtained in the study are presented as follows:1. Tea garden soils were spiked with a range of tetracycline or penicillin concentrations to study antibiotic effects on soil microbial community structure. The results showed that exogenous penicillin had certain inhibitory effect on bacteria, actinomyces and fungi. Compared with the control treatment (CK), the number of bacteria, fungi and actinomycetes decreased by80%,50%and50%, respectively, when the content of antibiotic was100mg/kg after incubation3weeks. Low content of tetracycline treatment could significantly inhibit the growth of bacteria and actinomycetes in tea garden soil, but no obvious inhibitory to fungi. The results of phospholipid fatty acid method (PLFA) showed that soil microbial community structure in tea garden was obviously changed under different penicillin and tetracycline treatment, eg. G-/G+increased. Moreover, PLFA20:0was abundant after incubation with tetracycline treatments, indicating that microbes characterized by PLFA20:0may be the main groups of anti-tetracycline bacteria.2. The effect of antibiotics (eight kinds of four categories) on soil microbial biomass (MB) and soil available nitrogen were investigated with different fertilization treatment. The results showed that antibiotics except azithromycin promoted the soil microbial biomass carbon (MBC), and also aminoglycoside and β-lactam antibiotics treatments increased soil microbial biomass nitrogen (MBN). However, macrolides and tetracycline reduced MBN. Soil microbial biomass nitrogen gradually restored during the incubation, indicating that carbon and nitrogen of antibiotics may be used by soil microorganism under1mg/kg treatment. Nitrate nitrogen contents increased under tetracycline class treatments with50mg/kg, N increased by50%and45.4%compared with CK in chlortetracycline and terramycin at7d of incubation, respectively. However, six of eight antibiotics reduced soil NO3--N, and the reductions of NO3--N increased with increase of antibiotic content. Two (erythromycin and terramycin) of eight reduced the content of soil NH4+-N, while6of8antibiotics increased soil NH4+-N significantly. The results suggested that all the antibiotic pollutions in our study affected transition between NO3--N and NH4+-N in soil, and the effects were different with different antibiotics. In this study, we found most of the antibiotics inhibited the conversion of NH4+-N to NO3--N, indicating that ammonia oxidation bacteria (AOB) and ammonia oxidation archaea (AOA) may be affected by antibiotic pollutions which need be further researched.3. We isolated5soil bacterial isolates (p4, p5, t1, t5, t9) from soil with the capacity to grow on antibiotic as sole carbon source. The bacterial isolates were identified based on analysis of the16S rRNA gene sequences. The bacteria were placed into a phylogenetic tree and were found to be surprisingly diverse. They were classified into five different genera, Lysobacter genus, Variovorax genus, Pseudomonas genus, Chitinophaga genus and Bradyrhizobium genus, respectively.4. We determined the multiple antibiotic resistance (MAR) of each of the five isolates against eight antibiotics covering four classes. All the resistant isolates from four soil samples showed MAR patterns for4or more antibiotics. The68%of the resistance to antibiotics changed after plasmid eliminated, indicating that most of the resistance genes were located in plasmid. The qualitative occurrence for tetracycline genes, β-lactams resistance genes and integrons genes in bacterial isolates using specific primer sets were analyzed by PCR method. The results showed tet(C) which codes for a tetracycline efflux pump were harbored in four bacterial isolates and blaTEM which codes for β-lactamase were harbored in all five isolates. Neither of the two integron genes were found in the isolates, suggesting a low risk of transmisson of the resistance genes. |
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