Penicillin << `pehn` uh SIHL ihn >> is a powerful drug used to treat infections caused by bacteria. It was the first antibiotic (drug produced by microbes) used successfully to treat serious diseases in human beings. Sir Alexander Fleming, a British scientist, discovered penicillin in 1928. Various forms of the drug, called penicillins, have become widely available for medical use since the mid-1940’s. Penicillins have played a major role in treating pneumonia, rheumatic fever, scarlet fever, and other diseases. The development of penicillins had a tremendous impact on medicine and encouraged research that led to the discovery of many other antibiotics.
Forms of penicillin.
There are many kinds of penicillin. They all come from molds of the genus (scientific group) named Penicillium << pehn uh SIHL ee uhm >>. Chemists isolate some natural penicillin substances by processing Penicillium molds in various ways. They produce other forms, called semisynthetic penicillins, by changing natural penicillin substances through chemical processes. Penicillin G is the most widely used natural penicillin. Commonly used semisynthetic penicillins are ampicillin << am puh SIHL ihn >>, amoxicillin << uh MOK suh sihl ihn >>, penicillin V, and nafcillin << NAF sihl ihn >>. Semisynthetic penicillins called extended spectrum and broad spectrum penicillins are effective against many types of bacteria. Two examples of such penicillins are ticarcillin << tihk uhr SIHL ihn >> and piperacillin << pihp uhr uh SIHL ihn >>.
How penicillins work.
Penicillins kill bacteria by preventing the formation of the stiff cell walls bacteria need to survive. Human cells do not form stiff cell walls, and so they remain undamaged by penicillins.
Some penicillins can be taken orally (by mouth). But stomach acids destroy other penicillins taken orally before they reach the bloodstream. Doctors usually give such penicillins as injections.
Most people who take penicillins experience no side effects, though some people suffer allergic reactions. These reactions are usually minor, causing fever or rashes. However, life-threatening reactions involving shock and breathing difficulties occur in some patients. Patients allergic to one form of penicillin will likely react to all forms. As a result, doctors treat some patients allergic to penicillin with antibiotics called cephalosporins << sehf uh luh SPAWR ihnz >>. These antibiotics are similar to penicillin and have been in use since the 1960’s.
Early history.
Fleming discovered penicillin in 1928 when he noticed mold growing in a lab dish containing common bacteria. He saw that the bacteria around the mold had died. In the 1930’s, British researchers led by Howard Florey and Ernst Chain found a way to extract (pull out) and purify small amounts of penicillin. In 1941, a British policeman with septicemia (blood poisoning) became one of the first people treated with the drug. He began to recover but died because the hospital lacked an adequate supply of penicillin.
During the next several years, researchers found ways to produce large quantities of some penicillins. One of these, penicillin G, proved the most effective. But penicillin G was not effective when given orally, and it did not kill certain bacteria. In the late 1950’s, chemists began making semisynthetic penicillins to overcome these problems. Most semisynthetic penicillins have one or more properties not found in penicillin G. For example, penicillin V kills the same bacteria as penicillin G, but blood absorbs it better. Ampicillin and amoxicillin are effective against some kinds of bacteria that penicillin G cannot kill. Doctors use these drugs to treat urinary tract infections, and throat and ear infections in children.
Resistance.
Since the 1950’s, many bacteria have become resistant to penicillin. Resistant bacteria are unaffected by certain penicillins or other antibiotics. Resistance can occur when the genes of a bacterium change in a way that makes it unaffected by a certain antibiotic. The bacterium’s offspring will also be unaffected by that drug. Bacteria can also become resistant by exchanging genetic material with other bacteria. One example of a kind of bacteria that often resists penicillin is Streptococcus pneumoniae << strehp tuh KOK uhs noo MOH nee eye >>, a cause of pneumonia. Most Staphylococcus aureus << staf uh luh KOK uhs AW ree uhs >> bacteria, which cause skin and bloodstream infections, are penicillin resistant. Penicillins are now ineffective in treating a commonly sexually transmitted disease called gonorrhea << gon uh REE uh >>.
The widespread use of antibiotics to treat infections in human beings and livestock increases the number of resistant bacteria. Resistance to antibiotics is a growing threat to public health.
