Penicillin is an antibiotic, which is extracted from Penicillium culture solution. The calcium salt, potassium salt or sodium salt of penicillin is usually used in medicine. Penicillin can inhibit staphylococcus, streptococcus, Neisseria gonorrhoeae and pneumococcus. The discovery of penicillin triggered the medical research on new antibiotics.

1928, when alexander fleming, a British bacteriologist, experimented with staphylococci, he found that some spores of Penicillium had contaminated his cultured staphylococci, and there was a staphylococci-free zone around the mold. After his research, he found that there is a substance in mold that can inhibit the growth of staphylococcus even if it is diluted 800 times. Through identification, Fleming knew that this mold belonged to Penicillium. Therefore, he called the filtered liquid containing this mold secretion "penicillin". Then Fleming inoculated the mold into Petri dishes of various bacteria and found that staphylococcus, streptococcus and diphtheria could be inhibited by it. After a series of experiments and studies, Fleming thinks that penicillin may become an antibacterial drug that can be applied to the whole body. 1929, Fleming published a paper and reported his findings. Until today, penicillin is still the most popular and widely used antibiotic.

There are many kinds of penicillin, which can be roughly divided into two categories. One is extracted from Penicillium culture solution, and the other is semi-synthetic penicillin synthesized by chemical methods, such as neopenicillin Ⅱ, ampicillin and cephalosporin. Commonly used are penicillin potassium salt and sodium salt powder, which have stable properties and can generally be preserved for several years. This powder is easily soluble in water, but after 24 hours of dissolution, it will not only cause the loss of antibacterial ability, but also decompose to produce various allergens. Therefore, it is very important to prepare penicillin now.

Penicillin is a widely used antibacterial drug with little toxicity, but the common adverse reaction is drug-induced allergy, and severe allergic reaction can even lead to death. The antibacterial effects of penicillin are: low concentration bacteriostasis and high concentration sterilization. It has a good killing effect on streptococcus, pneumococcus and gram-positive cocci, and also has an effect on sensitive staphylococcus and other bacteria. Clinically, penicillin is effective in treating pneumonia, tonsillitis, otitis media, cellulitis, bacterial endocarditis, osteomyelitis, epidemic meningitis, pneumococcal meningitis, syphilis, relapsing fever, gonorrhea, anthrax, tetanus and other diseases.