الفهرس 
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Abstract
1.1 Antibiotics,
An antibiotic is a chemical substance derived from or produced by various
species of microorganisms, which is capable in small concentrations of
inhibiting the growth of other microorganisms. Antibiotics are widely
distributed in nature, where they play an important role in regulating the
microbial population of soil, water and sewage. They differ markedly both
chemically and in their mechanism of action. The chemotherapeutic agents
interfere at a number of vulnerable sites in the cell.
They interfere with (1) cell wall synthesis, (2) membrane function, (3)
proteinsynthesis, (4) nucleic acid metabolism, and (5) intermediary metabolism.
Theremay be a number of stages between the initial or primary effect of the
drug and the eventual resultant death of the cell. Also, some agents may have
more than one primary site of attack or mechanism of action (Flynn, 1972;
Corcoran and Hahn, 1975; Tanaka, 1975).
1.1.1. Penicillin
1.1.1.1 IIistory,
In 1928, Alexander Fleming’s curiosity was aroused by
zonesof inhibition surrounding mold colonies contaminating a used petri dish.
On further investigation he concluded that the mold had secreted a compound.