The effect of tetracyclines used for swine food-production (tetracycline and oxytetracycline) on enriched nitrifying bacteria cultures over time was investigated in this study. Short-term exposure assays were performed in different concentrations of each antibiotic, using ammonia oxidizing bacteria (AOB) culture and nitrifying bacteria. The results pointed out a higher inhibitory effect of tetracycline on both bacterial communities. The AOB was more sensitive to antibiotic exposure when compared to the nitrifying culture. Although high antibiotic concentrations were applied, the half maximal inhibitory concentration (IC₅₀) was achieved only for the AOB culture exposed to tetracycline at a concentration of 273 mg L⁻¹. Nonetheless, the long-term exposure assay demonstrated a reduction of the tetracycline inhibition effect against AOB. The exposure to 100 mg L⁻¹ of tetracycline (TC) did not show relevant influence over ammonium conversion efficiency; however, at 128 mg L⁻¹ of TC, the efficiency decreased from 94% to 72%. Further investigation revealed that TC reduced the final effluent quality due to the development of a resistance mechanism by AOB culture against this antibiotic. This mechanism involves increasing the excretion of extracellular polymeric substances (EPS) and soluble microbial products (SMP), which probably increases BOD, and reduces ammonia consumption by the bacterial culture.

本研究研究了用于猪食品生产的四环素（四环素和土霉素）对硝化细菌富集培养的影响。使用氨氧化细菌（AOB）培养物和硝化细菌，以不同浓度的每种抗生素进行短期暴露试验。结果表明四环素对两个细菌群落具有更高的抑制作用。与硝化培养相比，AOB对抗生素的暴露更为敏感。尽管使用了高浓度的抗生素，但仅当暴露于四环素浓度为273 mg L ^-1的AOB培养物中，抑制最大浓度（IC ₅₀）达到一半。但是，长期暴露试验表明四环素对AOB的抑制作用降低。暴露于100 mg L ^-1的四环素（TC）中并没有显示出对铵转化效率的相关影响。然而，在TC为128 mg L ^-1时，效率从94％降低至72％。进一步的调查表明，由于AOB培养物对这种抗生素产生了耐药机制，TC降低了最终出水质量。该机制涉及增加细胞外聚合物（EPS）和可溶性微生物产物（SMP）的排泄，这可能会增加BOD并减少细菌培养产生的氨消耗。