Penicillin, discovered by Sir Alexander Fleming in 1928, was known as the "wonder drug" because of its ability to treat so many illnesses while not causing toxic side effects, according to information published by the University of Hawaii. Penicillin kills bacteria by binding to a bacterial enzyme required for the formation of the cell walls. By inhibiting the enzyme, the cell walls cannot form and the bacteria die. Penicillin is a general term used to describe a group of antibiotics. There are several types of penicillin that fall into three major groups, the natural penicillins, aminopenicillins and penicillinase-resistant penicillins.
Natural Penicillins
The natural penicillins include penicillin G and penicillin V. Penicillin G, also known as benzylpenicillin, is not stable in an acidic environment, such as in the stomach. Therefore, this penicillin is usually administered by injection although it does come in pill form. Penicillin V is more acid-resistant and is normally taken orally. These natural penicillins are highly effective against gram-positive bacteria (type of bacteria with a thick layer of peptidologlycan in the cell wall for the penicillin to attack) such as streptococci and staphylococci according to information published on The Microbial World. Natural penicillins in general are ineffective against gram-negative bacteria, except they do show some effectiveness against the meningococci that cause bacterial meningitis. They are also not effective against mycobacterium, such as mycobacterium tuberculosis that causes tuberculosis.
Aminopenicillins
Because the natural penicillins were limited in use against all types of bacteria, scientists started experimenting to find new modifications. The natural penicillins were chemically changed and with the addition of an amino group (a functional group that contains nitrogen) the aminopenicillins were founded. These semi-synthetic medications, meaning they are derived from a natural product by chemically changing the structure, are considered "broad-range" antibiotics because they are effective against the gram-positive bacteria as well as many of the gram-negative bacteria, including E. coli, Klebsiella and Haemophilus. The addition of the amino group enables the medication to penetrate the outer membranes of the gram-negative bacteria. The group of aminopenicillins includes amoxicillin, ampicillin and bacampicillin. Although aminopenicillins are not as active as the natural penicillins, their expanded spectrum of effectiveness makes them medically useful. The aminopenicillins are also tolerant of acid and can therefore be taken orally.
Pencillinase-Resistant Pencillins
There are some strains of bacteria, specifically those in the staphylococcal species, are resistant to the effects of penicillin. The resistance is due to their production of penicillinase, an enzyme produced by the bacteria that inhibits the actions of penicillin. New penicillins, known as penicillinase-resistant penicillins, were needed that had the ability to fight the bacteria and resist destruction by penicillinase. These medications, including cloxacillin, dicloxacillin, nafcillin, methicillin and oxacillin, are very effective in treating these gram-positive cocci bacteria in the Staphylococcal group but are not the best pills to choose for other bacteria due to their lower level of activity compared to other penicillins.
