Screening of soil bacteria for plasmids carrying antibiotic resistance

Summary To evaluate the role of plasmids in soil communities antibiotic-resistant bacteria have been isolated from soil. Among them, 419 l-aminopeptidase positive strains (Gram-negative) and 28 l-aminopeptidase negative strains (Gram-positive) were screened for the presence of plasmids. None of the Gram-negative organisms contained plasmids. Among the Gram-positive bacteria plasmid-harboring strains were detected.     

Combined effects of compost containing Sulfamethazine and zinc on pakchoi (Brassica chinensis L.) growth,soil sulfonamide resistance genes,and microbial communities

To understand the ecotoxicity of antibiotics and heavy metals in soil, 5% (w/w) composts containing different concentrations of sulfamethazine (SMZ) and/or zinc (Zn) were applied to soil to investigate their effects on pakchoi (Brassica chinensis L.) growth, soil sulfonamide resistance genes (SRGs: sul1, sul2, and dfrA7), and soil microbial communities. Composts containing less than 1.0 mg SMZ kg^–1 or less than 2.8 g Zn kg^–1 promoted pakchoi growth and the metabolic activity of soil microbial communities. Compared with the control, the absolute abundances (AAs) of soil SRGs significantly increased by 0.85–4.54 times with 50.6 μg kg^–1 SMZ treatment (P < 0.05), the AA of sul2 increased by 166% with 248.8 mg Zn kg^–1 treatment. The combination treatments with 19.8 μg SMZ kg^–1 and 179.9 mg Zn kg^–1 in soil had synergistic stimulatory effects on pakchoi growth, soil SRGs and microbial metabolism, whereas 53.5 μg SMZ kg^–1 and 262.1 mg Zn kg^–1 had an opposite effect. Pearson’s correlation analysis showed that carbon metabolism by soil microorganisms had significant positive correlations with shoot height of pakchoi (r = 0.84, P < 0.05) and AAs of SRGs (r > 0.80, P < 0.05).