Natural penicillin is obtained from penicillium culture medium. Among them, penicillin G is the first choice for clinical treatment of sensitive bacterial infections because of its stable nature and good efficacy.
Natural penicillin production can be divided into two steps: strain fermentation and extraction and purification. ① Strain fermentation: Penicillium chrysogenum Inoculate it on the solid medium and culture it at 25 ℃ for 7-10 days to obtain penicillium spore culture. Inoculate the spores into suspension with sterile water into the sterilized culture medium in the seed tank, inject sterile air, stir, culture at 27 ℃ for 24~28h, then inoculate the seed culture solution into the sterilized culture medium containing phenylacetic acid precursor in the fermentation tank, inject sterile air, stir, and culture at 27 ℃ for 7 days. In the fermentation process, phenylacetic acid precursor and appropriate medium should be added. ② Extraction and refining: cool the penicillin fermentation liquid and filter it. Under the condition of pH2~2.5, the filtrate is extracted by multistage countercurrent extraction with butyl acetate in the extractor to obtain butyl ester extraction solution, which is transferred to the buffer solution of pH7.0~7.2, and then transferred to butyl ester. The butyl ester extraction solution is decolorized by activated carbon, added with a salifying agent, and obtained penicillin G potassium salt through azeotropic distillation. Penicillin G sodium salt is used to pass penicillin G potassium salt through ion exchange resin (sodium type). 
