Talking about antibiotics, it is familiar to modern people. Large-scale production of antibiotics began in the 1940’s. Nowadays, millions of tons of antibiotics are used annually in the world. Besides widely used to cure human diseases, antibiotics also play important roles in livestock production as growth promoters. However, people seldom notice that antibiotics are easily excreted by the drug receptors. And once excreted, especially for broad-spectrum antibiotics, they are suspected to influence non-target microorganisms in environment.

“Once antibiotics enter soil through land application of manure, sludge, and wastewater, it is suspected that they will cause pollution or other environmental risks.” said researcher LIU Feng in Institute of Subtropical agriculture, Chinese Academy of Sciences (ISA). The question that the relevance of antibiotics persistence in the soil and their effects on the soil microbial community function is brothering ISA researchers.

“We spike two common broad-spectrum antibiotics －sulfamethoxazole(SMX) and chlortetracycline(CTC) in a loam paddy soil and incubate for 21 days.” said LIU. Then researchers analyzed the dose-effect and time-dependent changes of antibiotic-associated disturbance on soil microbial community using Biolog EcoPlate.

They find that SMX decrease functional diversity of soil microbial community in the early incubation period, but change to improve soil microbial community function in the late. CTC has less effect on soil microbial community function during the whole experiment. As compared to the significant effects of low oxytetracycline concentration on the microbial community reported by Dr. KONG Weidong, the two tested antibiotics are directly spiked into soil, but less inhibitory effectiveness on soil microbial community function is found.

Analyzing the data, researchers come to the conclusion that SMX and CTC have different adsorption tendency to soil. The strong adsorption of CTC with soil results in low bioavailability for soil bacteria and mitigates the antibacterial effects. Meanwhile, the fast dissipation of SMX in the soil play certain roles in reducing effects on soil microbial community in the late incubation period. Their findings demonstrate that antibiotic addition may exert a selective pressure on the metabolic activity of subgroups of the overall soil microbial community, and the suppression could be easily compensated by other species. Therefore, soil microbial community function recovers or improves due to antibiotic dissipation in soil.

The main findings of this study have published on Applied Microbiology and Biotechnology(doi: 10.1007/s00253-011-3831-0),detail can be reached at http://www.springerlink.com/content/t1835up167540781/.