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Antibiotics
By
Dr. Humodi A. Saeed
Associate Prof. of Medical Microbiology
College of Medical Lab. Science
Sudan University of Science and Technology
E mail address: [email protected]
Definition of Antibiotic
A substance of biological, semisyntheticor
synthetic origin of low molecular weight
(on-protein) produced by a fungus or
bacterium as secondary metabolites that
inhibits or stop growth of other
microorganisms in vitro and in vivo
selectively, when it used
in low
concentration
Characteristics of Antibiotics
It must be able to 
reach the part of the
human body where
the infection is
occurring.
Characteristics of Antibiotics
It should not cause 
the development of
resistant forms of
parasites.
Characteristics of Antibiotics
It should not 
produce undesirable
side effects in the
host such as
allergic reaction,
nerve damage or
irritation of the
kidneys and
gastrointestinal
tract.
Characteristics of Antibiotics
It should be given 
orally without
inactivation by
stomach acid, or by
injection
(parenterally)
without binding to
the blood proteins.
Characteristics of Antibiotics
Finally, it should 
have a high level of
solubility in the
body fluids and be
possible to achieve
concentrations in
the tissue or blood,
which are
sufficiently high to
inhibit or kill the
infectious agent.
Major groups of Antibiotics
1. Beta-lactam
antibiotics
1. Penicillins
2. Cephalosporins
3. Carbapenems
4. Monobactams
1. Beta-lactam antibiotics
Toxicity Problem
The main toxicity 
problem with these
antibiotics is an allergic
reaction that occurs
because of formation of
beta-lactam/serum
protein conjugate that
elicits an inflammatory
immune response.
1. Beta-lactam antibiotics
Mode of Action
The beta-lactam 
antibiotics inhibit
the last step in
peptidoglycan
synthesis
1. Beta-lactam antibiotics
Spectrum
Some are effective 
against both Grampositive and Gramnegative bacteria
whereas others are
more effective
against Grampositive than Gramnegative bacteria or
vice versa.
1. Beta-lactam antibiotics Example
1. ( Natural penicillins and
cephalosporins )
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Penicillin G, Cephalothin
Biological source
Penicillium notatum
Cephalosporium species
Spectrum (effective against)
Gram-positive bacteria
Mode of action
Inhibits steps in cell wall (peptidoglycan)
synthesis.
1. Beta-lactam antibiotics
Example 2. ( Semisynthetic penicillin)
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Ampicillin, Amoxycillin
Spectrum (effective against)
Gram-positive and Gram-negative bacteria
Mode of action
Inhibits steps in cell wall (peptidoglycan)
synthesis.
1. Beta-lactam antibiotics
Example 3. (Clavulanic Acid )
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Clavamox is clavulanic acid plus
amoxycillin
Biological source
Streptomyces clavuligerus
Spectrum (effective against)
Gram-positive and Gram-negative bacteria
Mode of action
Suicide inhibitor of beta-lactamases
Example 4. (Monobactams )
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Aztreonam
Biological source
Chromobacter violaceum
Spectrum (effective against)
Gram-positive and Gram-negative bacteria
Mode of action
Inhibits steps in cell wall (peptidoglycan)
synthesis and murein assembly
1. Beta-lactam antibiotics
Example 5. ( Carboxypenems )
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Imipenem
Biological source
Streptomyces cattleya
Spectrum (effective against)
Gram-positive and Gram-negative bacteria
Mode of action
Inhibits steps in cell wall (peptidoglycan)
synthesis.
2. Glycopeptides
Another group of peptidoglycan
synthesis inhibitors is the
glycopeptides, exemplified by
vancomycin and teichoplanin.
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2. Glycopeptides
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Vancomycin
Biological source
Streptomyces orientales
Spectrum (effective against)
Gram-positive bacteria, esp. Staphylococcus
aureus
Mode of action
Inhibits steps in murein (peptidoglycan)
biosynthesis
3. Aminoglycosides
Members of this group contain sugars and consists
of streptomycin, dihydrostreptomycin, neomycin,
framycetin, gentamicin, kanamycin, paromycin,
tobramycin and amikacin.
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3. Aminoglycosides
 Example
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1.
Gentamicin
 Biological source
 Micromonospora species
 Spectrum (effective against)
 Gram-positive and Gram-negative bacteria esp.
Pseudomonas
 Mode of action
 Inhibit translation (protein synthesis)
3. Aminoglycosides
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Example 2
Streptomycin
Biological source
Streptomyces griseus
Spectrum (effective against)
Gram-positive and Gram-negative bacteria
Mode of action
Inhibit translation (protein synthesis)
4. Tetracyclines
Tetracyclines consist of eight members, and 
may be considered as a group of antibiotics,
obtained as byproducts from the metabolism
of various species of Streptomyces .
4. Tetracyclines
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Example 1.( Natural )
Tetracycline
Biological source
Streptomyces species
Spectrum (effective against)
Gram-positive and Gram-negative bacteria,
Rickettsias
Mode of action
Inhibit translation (protein synthesis)
4. Tetracyclines
 Example
2. (Semisynthetic tetracycline)
Doxycycline
 Spectrum (effective against)
 Gram-positive and Gram-negative
bacteria, Rickettsias Ehrlichia, Borellia
 Mode of action
 Inhibit translation (protein synthesis)
5. Macrolides
Macrolides are an ill-defined group 
representing those antibiotics that have large
ring structures containing oxygen.
5. Macrolides
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Example
Erythromycin
Biological source
Streptomyces erythreus
Spectrum (effective against)
Gram-positive bacteria, Gram-negative
bacteria not enterics, Neisseria,Legionella,
Mycoplasma
Mode of action
Inhibits translation (protein synthesis)
6. Lincosamides
Lincosamides are a family of antibiotics that 
bind to bacterial 50S ribosomal subunit. They
differ considerably from macrolides in
structure.
6. Lincosamides
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Example
Clindamycin
Biological source
Streptomyces lincolnensis
Spectrum (effective against)
Gram-positive and Gram-negative bacteria
esp. anaerobic Bacteroides
Mode of action
Inhibits translation (protein synthesis)
7. Quinolones
Quinolones are a family of antibiotics that 
interferes with DNA replication. Quinolones
are bactericidal antibiotics.
Nalidixic acid
Ciprofloxacin
Norfloxacin
Ofloxacin
8. Rifampin
Rifampin (or Rifampicin) is an antibiotic that 
inhibits bacterial RNA polymerase by binding
to its ß-subunit. Rifampin is a bactericidal
antibiotic.
9. Polypeptides
 Example
1
 Polymyxin
 Biological source
 Bacillus polymyxa
 Spectrum (effective against)
 Gram-negative bacteria
 Mode of action
 Damages cytoplasmic membranes
9. Polypeptides
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Example 2
Bacitracin
Biological source
Bacillus subtilis
Spectrum (effective against)
Gram-positive bacteria
Mode of action
Inhibits steps in murein (peptidoglycan)
biosynthesis.
10. Polyenes
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Example 1.
Amphotericin
Biological source
Streptomyces nodosus
Spectrum (effective against)
Fungi
Mode of action
Inactivate membranes containing sterols
10. Polyenes
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Example 2.
Nystatin
Biological source
Streptomyces noursei
Spectrum (effective against)
Fungi (Candida)
Mode of action
Inactivate membranes containing sterols
11. Rifamycins
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Examples
Rifampicin
Biological source
Streptomyces mediterranei
Spectrum (effective against)
Gram-positive and Gram-negative bacteria,
Mycobacterium tuberculosis
 Mode of action
 Inhibits transcription (eubacterial RNA
polymerase)
12. Phenols
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Example
Chloramphenicol
Biological source
Streptomyces venezuelae
Spectrum (effective against)
Gram-positive and Gram-negative bacteria
Mode of action
Inhibits translation (protein synthesis)
Resistance to Antibiotics
Resistance to Antibiotics
Resistance to Antibiotics
Resistance to Antibiotics
Resistance to Antibiotics
Antibiotics Susceptibility Tests