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• Firstly, bactericidal antibiotics (e.g. Penicillin and Cephalosporin) kill bacteria
by inhibiting cell wall synthesis and allowing cell contents to leak out. Even
though human and animal cells do not have cell walls, these antibiotics do not
damage cells.
• Secondly, bacteriostatic antibiotics (including tetracycline, erythromycin) stop
bacteria from reproducing by inhibiting nucleic acid formation (DNA and RNA)
or by inhibiting protein synthesis by cell structures called ribosomes.
Antibiotics that inhibit DNA and RNA affect bacterial cells more than human or
animal cells. Antibiotics that inhibit protein synthesis can cause side effects
because some human and other animal ribosomes are similar to those in
bacteria (Johnson, 2001).
Antibiotics can also be categorized by the type of bacteria they affect. The cell wall of
some species of bacterium is made of a thick layer of peptidoglycan. Gram-negative
bacteria have a thin layer of peptidoglycan combined with both an outer and inner
membrane. These differences in structure can be seen when bacteria are Gram-
stained. Bacteria with thick peptidoglycan can appear purple when stained and are
referred to as Gram-positive. Bacteria with thin peptidoglycan appear colourless or
red and are referred to as Gram-negative (Johnson, 2001).
As from 1999 the antibiotic manufacturing has increased 25 times from 907 198 164
kgs to over 22 679 954 096 kgs each year (Johnson, 2001). While these drugs are
still the best defense against bacterial infections, more and more of these
compounds are also being used against illnesses that cannot be cured by the other
current medications. When antibiotics first appeared about 50 years ago, they were
rightly hailed as a modern medical miracle. Until that time, bacterium-related
infections, such as meningitis and typhoid fever, often led to death. Antibiotics have
saved millions of lives and have had relatively had few side effects. Presently, the
term, antibiotic, is more commonly used to refer to synthetic or partly synthetic
compounds used medically against bacteria that cause illness in humans, animals
and plants. Penicillin and erythromycin are two of the most widely used antibiotic
drugs. The microorganisms have an amazing adaptability for mutation to adjust to
the environment. The misuse of antibiotics in our medical practice is certainly a
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