👉 In microbiology, a penicillin is an antibiotic that was discovered in 1928 by the German chemist Alexander Fleming. Penicillium species are bacteria that produce penicillin, which is a type of antibiotic. Penicillium is one of the most common types of gram-positive bacteria and is commonly found in soil, water, and certain environments. The specific strain of penicillin used for treatment depends on the patient's condition and the severity of their infection.