: any of several antibiotics or a mixture of these produced by penicillia or in the laboratory and used especially against round disease-producing bacteria. from scientific Latin Penicillium a genus of molds producing antibiotics, from Latin penicillus, literally, little tail — related to pencil. Penicillins were among the first medications to be effective against many bacterial infections caused by staphylococci and streptococci. They are still widely used today for various bacterial infections, though many types of bacteria have developed resistance following extensive use. Penicillins are antibiotics used to treat bacterial infections that are derived from the antibiotic penicillin. Penicillin antibiotics stop bacteria from multiplying by preventing bacteria from forming the walls that surround them. Penicillin G benzathine injection is used to treat bacterial infections (eg, mild to moderate infections of the upper respiratory tract, syphilis, yaws, bejel, pinta). Penicillin, antibiotic derived from Penicillium mold, one of the first antibiotics to be discovered. Penicillins are a type of antibiotic derived from Penicillium fungi. An antibiotic is a type of medicine that inhibits the growth of, or kills, bacteria. Penicillin G (also called benzylpenicillin) was discovered by accident in 1928. Penicillin is a type of antibiotic that treats bacterial infections like pneumonia and strep throat. Some bacteria have become resistant to penicillin, making the drug less effective. Overview: Penicillin is an antibiotic that is used to treat bacterial infections. It kills certain types of bacteria by blocking their ability to create their cell wall. The most common side. Penicillin is a group of antibiotics (medications used to treat bacterial infections) that work in a specific way to destroy bacteria in your body. Types of penicillin and drugs closely related to them are called “penicillins.” Penicillin's discovery by Alexander Fleming in 1929 gets a lot of hype as the advent of antibiotics. But in reality, Fleming was just one part of the story..