Variations in dissipation rate, microbial function and antibiotic resistance due to repeated introductions of manure containing sulfadiazine and chlortetracycline to soil.

Antibiotic persistence following five successive treatments of sulfadiazine (SDZ) and chlortetracycline (CTC), alone and in combination, in manure-amended soil was studied under laboratory conditions. The resulting effects on soil respiration and enzyme activities as well as pollution-induced community tolerance, were also examined. A trend of initial suppression followed by recovery was observed in the dissipation rates of SDZ or CTC during the antibiotic treatments, and combined treatment with both antibiotics did not alter the respective dissipation rates significantly. Soil respiration activity with SDZ and/or CTC treatments was inhibited during the initial two treatments; however, the activity thereafter recovered to or exceeded the level of the individual manure treatment. Initially, soil urease and dehydrogenase activities were not affected; however, after the fifth treatment, these activities were significantly stimulated in the CTC individual and combined treatments compared with their activities in the individual manure treatment. Bacterial community tolerance to SDZ and CTC in manure-amended soil increased significantly (p⩽0.05) with antibiotic treatment frequency.