Veterinary antibiotic oxytetracycline’s effect on the soil microbial community

Antibiotics are widely used to treat animals from infections. After fertilizing, antibacterials can remain in the soil while adversely affecting the soil microorganisms. The concentration of oxytetracycline (OTC) in the soil and its effect on the soil microbial community was assessed. To assess the impact of OTC on the soil microbial community, it was added to the soil at concentrations of 50, 150, and 300 mg kg–1 and incubated for 35 days. The concentration of OTC added to the soil decreased from 150 to 7.6 mg kg–1 during 30 days of incubation, as revealed by LC-MS. The deviations from the control values in the level of substrate-induced respiration on the 5th day of the experiment were, on average, 26, 68, and 90%, with OTC concentrations at 50, 150, and 300 mg kg–1, respectively. In samples with 150 and 300 mg kg–1 of OTC, the number of bacteria from the 3rd to 14th day was 2–3 orders of magnitude lower than in the control. The addition of OTC did not affect the fungal counts in samples except on the 7th and 14th days for the 150 and 300 mg kg–1 contaminated samples. Genes tet(M) and tet(X) were found in samples containing 50, 150, and 300 mg kg–1 OTC, with no significant differences in the number of copies of tet(M) and tet(X) genes from the OTC concentration. Our results showed that even after a decrease in antibiotic availability, its influence on the soil microbial community remains.