Overview on Penicillin and Antibiotics
                     Overview on 
Penicillin and 
Antibiotics
Introduction
Antibiotic, chemical substance produced by a living organism, generally 
a microorganism, that is detrimental to other microorganisms. 
Antibiotics commonly are produced by soil microorganisms and probably 
represent a means by which organisms in a complex environment, such 
as soil, control the growth of competing microorganisms
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Introduction of Penicillin
Antibiotics came into worldwide prominence with the introduction of 
penicillin in 1941. Since then they have revolutionized the treatment of 
bacterial infections in humans and other animals. They are, however, 
ineffective against viruses.
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The first antibiotics
In 1928 Scottish bacteriologist Alexander Fleming noticed that colonies 
of bacteria growing on a culture plate had been unfavourably affected by 
a mold, Penicillium notatum, which had contaminated the culture. 
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Development of antibiotics
A decade later British biochemist Ernst Chain, Australian pathologist 
Howard Florey, and others isolated the ingredient responsible, penicillin, 
and showed that it was highly effective against many serious bacterial 
infections. 
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Semisynthetic versions
Toward the end of the 1950s scientists experimented with the addition of 
various chemical groups to the core of the penicillin molecule to 
generate semisynthetic versions.
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Administration of 
antibiotics
The principle governing the use of antibiotics is to ensure that the 
patient receives one to which the target bacterium is sensitive, at a high 
enough concentration to be effective but not cause side effects, and for 
a sufficient length of time to ensure that the infection is totally 
eradicated.
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Use of antibiotics
Antibiotics vary in their range of action. Some are highly specific. Others, 
such as the tetracyclines, act against a broad spectrum of different 
bacteria. These are particularly useful in combating mixed infections and 
in treating infections when there is no time to conduct sensitivity tests
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Categories of antibiotics
Antibiotics can be categorized by their spectrum of activity—namely, 
whether they are narrow-, broad-, or extended-spectrum agents. 
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Mechanisms of action
Antibiotics produce their effects through a variety of mechanisms of 
action. A large number work by inhibiting bacterial cell wall synthesis; 
these agents are referred to generally as β-lactam antibiotics.
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Antibiotic resistance
A problem that has plagued antibiotic therapy from the earliest days is 
the resistance that bacteria can develop to the drugs. 
An antibiotic may kill virtually all the bacteria causing a disease in a 
patient, but a few bacteria that are genetically less vulnerable to the 
effects of the drug may survive. 
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