Antibiotics residues have been accumulating in the environment day by day due to overuse of antibiotics.  Recalcitrant antibiotic residues, such as tylosin (TYL), can cause serious environmental problems, which makes it important to eliminate TYL from the environment.  It is important to eliminate TYL from the environment.  In this study, a strain was isolated and purified from fermentation by-product that came from a TYL production factory.  The TYL degrading strain was identified by its morphology, physiological and biochemical reactions and sequencing the PCR-amplified fragments of its 16S rDNA-coding genes.  The temperature, shaking speed, initial TYL concentration, pH and inoculum sizes were investigated under simulated conditions by using single factor tests.  The results showed that TYL2, a high efficient strain was isolated and was identified as Brevibacillus borstelensis.  The degradation rate of TYL by this strain could reach to 75% with an initial concentration of 25 mg L^–1 within 7 days under conditions of 7% B. borstelensis (v/v, 2×10⁸ CFU mL^–1) at pH 7.0 and at 35°C.  It is interesting that this strain has a very strong ability to degrade the TYL in natural sewage with the degradation rate of 65% within 7 days.  This result could be helpful for the degradation of TYL and provide guidance for the degradation of other antibiotics.

Over the past few decades, the usage of oxytetracycline (OTC), a kind of antibiotic, has increased with the development of aquaculture and livestock breeding.  However, about 30–90% of the applied antibiotics are excreted as the parent compounds into the environment, especially with the application of animal manure to agricultural fields.  This large influx of antibiotics may lead to the destruction of the natural microbial ecological community and pose great threats to human beings through the food chain.  Therefore, the fate and toxicity of OTC in the environment are issues of great concern.  Degradation of OTC, including the non-biodegradation and biodegradation, and the biological toxicity of its degradation products or metabolites, are reviewed in this paper.  The non-biodegradation pathways include hydroxylation, quinonization, demethylation, decarbonylation, dehydration and secondary alcohol oxidation.  Light (particularly UV light), pH and oxidizing substances play important roles in non-biodegradation.  Biodegradation products include 4-epi-OTC (EOTC), 2-acetyl-2-decarboxy-amido-OTC (ADOTC), α-apo-OTC and β-apo-OTC.  EOTC is an epimer and identied except for the configuration of the C4 dimethylamino group of OTC.  Temperature and pH are the main factors affecting biodegradation pathways of OTC.  In addition, this review discusses concerns over the biological toxicity of OTC degradation products.