What Are Antibiotics?
The first effective antibacterial agents, the sulfonamides, were developed
in the 1930s and are still used today. These drugs only killed a limited
number of bacterial species and had no effect on many important diseasecausing
microbes. The use of penicillin and other antibiotics, beginning
in the 1940s, revolutionized the practice of medicine, because these drugs
were able to stop many otherwise deadly pathogens (organisms that cause
disease) in their tracks.
THE DISCOVERY OF PENICILLIN
Sir Alexander Fleming was a microbiologist at St.Mary’s Hospital in London
(Figure 1.1). During the late 1920s he was studying an important
human pathogen, Staphylococcus aureus. During the summer of 1928,
Fleming went on an extended vacation, and he left some cultures of S.
aureus in petri plates on his lab bench.When Fleming returned from his
vacation, he briefly checked the plates that had been sitting out. Initially,
he discarded the now-famous plate into a tray of disinfectant. Fortunately,
he had such a large pile of discarded plates that they didn’t all get submerged
in the antibacterial liquid. A colleague then appeared in the lab,
and to make a point, Fleming picked up the famous plate and happened
to notice something unusual. On that plate a mold (now called Penicillium
notatum) had grown. Surrounding this fungus was a clear zone,
where the S. aureus had been killed (Figure 1.2). Fleming had previously
done work with other substances that killed bacteria, and he quickly recognized
the significance of his observation.2
Following his discovery, Fleming made some crude extracts of the
material from the fungus and found that this material killed manydifferent types of important
pathogenic bacteria. He also
found he could inject this crude penicillin extract into rabbits,
and the rabbits weren’t harmed.However, Fleming wasn’t able
to extract and purify a significant amount of penicillin, so his
discovery languished for the next 10 years.
In 1938, three other English Scientists—Howard Florey,
Ernst Chain, and Norman Heatley—started working on producing
large amounts of penicillin. Despite the outbreak ofWorld War II they had made substantial
progress by 1941. By
then, however, German planes were regularly attacking England,
and there was concern that work on penicillin in Britain
would be difficult under wartime conditions. Consequently,
Florey and Heatley traveled to the United States to gain support
for the large-scale production of penicillin and to assist
with the process. A series of incremental improvements
involving new fungal strains, better growth media, and otherdevelopments finally led to the
production of enough penicillin
to treat soldiers wounded in the D-Day invasion in
1944. Antibiotics are truly wonder drugs, and today they cure
thousands of infected people each day. But what are they?
Antibiotics are small molecules usually produced by bacteria
or fungi that kill bacteria without harming the person or animal
being treated. Chemically synthesized compounds are
sometimes called antibacterial agents, but in this book, both
synthetic and naturally produced antibacterial compounds
will be called antibiotics. Antibiotics are distinguished fromantiseptics (antibacterial chemical
agents, such as detergents,
only suitable for application to the skin) and disinfectants
(strong antibacterial chemicals, such as bleach, only suitable for
treating inanimate objects). Antibiotics are also distinguished
from antifungal agents, which specifically kill molds and yeasts,
and antiviral agents, which prevent viruses from replicating.
Antibiotics are only effective on bacteria; they do not kill viruses
such as HIV or fungi, like those that cause athlete’s foot.