M. Sc. Presentation

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WHAT ARE ANTIBIOTICS FOR?
1.An antibiotic is given for the treatment of an infection caused by
bacteria.
2. Antibiotics target microorganisms such as fungi and protozoa .
However, they are not effective against viruses.
3.A broad-spectrum antibiotic can be used to treat a wide range of
infections.
4.A narrow-spectrum antibiotic is only effective against a few
types of bacteria.

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10. 1. Proteins vital for growth and repair
2. Act either at:
A. Site of protein synthesis (ribosome)
B. Within the nucleus by inhibiting synthesis of
nucleic acids
C. DNA replication / RNA synthesis = TRANSCRIPTION
Eg. Tetracyclines, aminoglycosides and
macrolides (erythromycin)
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11. 3.INHIBITION OF MEMBRANE FUNCTION:-
1. Essentially, affect cell membrane
transportation in and out
2. Increases permeability of membrane
-External influences have greater effect
-Microbe death
Eg. Polymyxin, Colistin
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12. 1.Interference with Nucleotide Synthesis
2. Inhibition of DNA-Directed RNA Polymerase
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5.ANTIMETABOLITES:-
They are closely resembles with the normal substrate
for the enzyme.
Eg- Sulfanilamide= paraaminbenzoic acid(PABA)
synthesis of folic acid

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17. 1. Nature:-Bactericidal
2. Mode of action :-
bind to the 30s ribosomal subunit and
interfere with protein synthesis
by directly inhibiting the
synthesis process .
induce misreading of the mRNA.
3. Spectrum of Activity
these are active against many gram-negative and some gram-
positive bacteria. They are not useful for anaerobic bacteria, since
oxygen is required for uptake of the antibiotic, or for intracellular
bacteria.
eg:Streptomycin, kanamycin, gentamicin
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18. 1. Nature:-Bacteriostatic
2. Mode of action
The macrolides inhibit translocation of the peptidyl tRNA from the A
to the P site on the ribosome by binding to the 50S ribosomal 23S
RNA.
3. Spectrum of activity
Gram-positive bacteria, Mycoplasma, Legionella
Eg:-Erythromycin ,Azithromycin
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19. 1. Nature:- Bacteriostatic
2. Mode of action
These antibiotics are similar to the aminoglycosides .
It is combine with the 30S subunit of the ribosome.
This inhibits the binding of aminoacyl-t RNA molecules to the A
site of the Ribosome.
3. Spectrum of activity -
These are broad spectrum antibiotics and are useful against
intracellular bacteria
Eg:-Tetracycline, minocycline and doxycycline
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20. 3.Spectrum of activity :-
These are broad spectrum antibiotics and are useful against
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22. 1.Fusidic acid:-
1. Nature:-Bacteriostatic
2. Mode of action
Fusidic acid binds to elongation factor G (EF-G) and inhibits release of EF-G from
the EF-G complex.
3. Spectrum of activity
Fusidic acid is only effective against gram-positive bacteria such as Streptococcus,
Staphylococcus aureus and Corynebacterium minutissimum.
2.Chloramphenicol:-
1.Nature:- Bacteriostatic
2.Mode of action
These antimicrobials bind to the 50S ribosome and inhibit peptidyl transferase
activity.
3.Spectrum of activity
Broad spectrum and
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WHAT ARE THE SIDE-EFFECTS OF ANTIBIOTICS?
1.The most common side-effects of antibiotics:
1. Diarrhea
2. Feeling and being sick
3. Allergic reactions
2.Below is a list of rare side-effects of antibiotics:
1. Formation of kidney stones (when taking sulphonamides)
2. Abnormal blood clotting (when taking some
cephalosporins)
3. Sensitivity to sun (when taking tetracyclines)
4. Deafness (when taking erythromycin and the
aminoglycosides)

27. 1. Antibiotics are clearly one of the greatest triumphs of
medical sciences, but they have a limited range of
targets.
2. Unfortunately, the problem of antibiotic resistant has
now reached a crisis point.
3. Microbes are now developing resistance to these
modes of action.
4. A first step will be to modify existing drugs to extend
their spectrum and prevent their destruction by
bacterial enzymes of resistance.
5. Research is underway to prevent the resistant
strategy of rapid antibiotic efflux.
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CONCLUSION:-
1. Most of our present antibiotics are the products of
other microorganisms.
2. Interest is now also focusing on antibiotics produced
by plants and animals that often exhibit
extraordinary resistance to microbial infections.
3. The sale of antimicrobial drugs is big business.
4. Because of the massive quanities of antibiotics being
prepared and used,an increasing number of diseases
are resisting treatment due to the spread of drugs.

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Any
Question???

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1.Joanne M.Willey,Linda M.Sherwood,Christopher J .Woolverton
Prescott,Harley,and Kelin’s Microbiology.
2.A Textbook of Microbiology
R.C.Dubey,D.K.Maheshwari.

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