Research on the Degradation Performance of Avermectin by Two Microbial Strains Avermectin is a typical macrolide antibiotic commonly used as a veterinary drug and plays an important role in animal husbandry. With the vigorous development of animal husbandry, the demand for antibiotics by humans is also increasing day by day. At present, the annual production and use of antibiotics in China is about 189000 tons, of which a large part is applied in animal husbandry. The use of veterinary antibiotics accounts for more than half of the total amount of antibiotics used in animal husbandry. In 2010, China surpassed Japan and the United States in terms of animal drug raw materials and usage, becoming the world’s largest user of animal drug raw materials. However, the extensive use of antibiotics can lead to serious consequences. After entering the organism, some veterinary antibiotics are absorbed, while others exceed the tolerance range of the treated livestock and are excreted from the body. With the help of migration, antibiotics are transferred to different ecosystems, continuously accumulating in water and soil, which can affect the normal functioning of organisms in the environment. Therefore, efficient and simple treatment of residual antibiotics in the current environment to prevent further harm to organisms has become a hot research topic.

At present, the main methods for treating antibiotics include physical adsorption, advanced oxidation, and microbial degradation. Due to the increasing awareness of environmental protection among people, microbial degradation has become a favored technology among researchers. At present, the reported microorganisms that can degrade avermectin mainly include Bacillus subtilis, Acinetobacter lwofi, Shigella, white rot fungi, etc. They usually use macrolide degrading enzymes produced by metabolism to degrade avermectin. However, most studies only study the degradation characteristics of microorganisms on avermectin through single factor experiments without further analysis using orthogonal or response surface methodology, and cannot accurately determine the optimal degradation conditions. Therefore, in this experiment, avilamycin was used as a representative antibiotic. High performance liquid chromatography was used to measure the degradation characteristics of Bacillus subtilis and Shigella on avilamycin under different temperature, pH, sample volume, strain liquid volume, and cultivation time conditions. Response surface methodology was used to analyze the degradation characteristics and obtain the optimal conditions for the microbial strain to degrade avilamycin, in order to provide a basis for the practical application of microbial degradation of avilamycin and other veterinary antibiotics.

 

In recent years, with the gradual development of green industry, the use of microbial strains for degradation in the treatment of environmental pollutants has gradually become a favored topic for researchers. Due to the poor water solubility of avermectin, its degradation cycle in microbial degradation methods is longer than that of tetracycline and β – lactam antibiotics, and it usually takes more than 15 days to achieve a degradation effect of over 80%. Research has shown that only a small number of strains can degrade avermectin more efficiently. For example, Burkholderia can degrade about 80% of avermectin within 48 hours, and thermophilic Bacillus can achieve a degradation rate of 77.6% of avermectin standard within 72 hours. Therefore, studying and screening specific bacterial strains is beneficial for the further development of microbial degradation methods.

Bacteria generally degrade macrolide antibiotics by metabolizing them to produce inactivating transferases. These inactivating transferases can be mainly divided into macrolide esterases, 2 ‘- glycosylphosphorylate transferases MPH1, and glycosylphosphotransferases, which can promote the phosphorylation and glycosylation of antibiotic molecular structures, thereby causing antibiotics to lose their original properties. However, the degradation mechanism of strains commonly used for antibiotic treatment has not been fully explored, which is also a difficult problem that researchers need to solve today. Meanwhile, recent studies have also reported some strains capable of producing macrolide inactivating enzymes, but no subsequent degradation performance tests have been conducted, such as Mycoplasma pneumoniae, Streptococcus suis, Pseudomonas aeruginosa, etc.
Based on the current research status and existing problems, the development direction of bacterial degradation of avermectin can be divided into the following points: ① Further research on the mechanism of microbial strain degradation of avermectin, providing a basis for the screening of degradation strains. ② By screening and combining different microbial strains, better degradation effects can be achieved Reduce production costs, select affordable culture media, and cultivate strains with short production cycles Selecting strains that are environmentally friendly and free from secondary pollution can effectively prevent secondary pollution to the environment.
In the strain screening experiment, Bacillus subtilis showed a high degradation rate of 21.76% for avermectin; The degradation rate of Shigella is slightly lower than that of Bacillus subtilis, at 17.91%. This indicates that Bacillus subtilis and Shigella have strong degradation ability towards avermectin. Further exploration of the degradation performance of these two bacteria revealed that under optimized conditions, both Bacillus subtilis and Shigella have shown good performance in actual degradation. However, compared to Bacillus subtilis, Shigella has a lower optimal degradation temperature, which is beneficial for reducing energy consumption during actual degradation. However, Shigella is a common pathogenic bacterium that may cause secondary pollution when dealing with residual avermectin in the environment; Bacillus subtilis is a non pathogenic bacterium that does not have a significant impact on the environment and human health. Therefore, it can be directly used in treatment structures without the need for disinfection, making it safer, more environmentally friendly, and suitable for practical applications.