An antibiotic is a chemical substance produced by microorganisms that inhibits the growth of other microorganisms in small concentrations. Antibiotics can be classified based on their mechanism of action such as inhibiting cell wall synthesis, protein synthesis, or DNA synthesis. They can also be classified based on their spectrum of activity as narrow, broad, bacteriostatic, or bactericidal. Common classifications include antibiotics that inhibit cell wall synthesis like penicillins and cephalosporins, inhibit protein synthesis like tetracyclines and erythromycin, or inhibit DNA synthesis like fluoroquinolones.

2. •An antibiotic is a chemical substance produced by various species of
microorganisms that is capable in small concentrations of inhibiting the growth
of other microorganisms
Old:
•An antibiotic is a product produced by a microorganism or a similar substance
produced wholly or partially by chemical synthesis, which in low
concentrations, inhibits the growth of other microorganisms. They are the
agents which either kill or inhibit the growth of bacteria through various
mechanisms.
Updated:
Definitions of Antibiotics

3. Micro-organisms
They are the organisms which cannot be seen with
the naked eyes and need a microscope for
visualization
They can cause several infections and health
problems
They have all the characteristics of living organisms
including Reproduction, Growth, Nutrition and
Excretion
Several antibiotics have been discovered as cure for
various classes of microbes

4. Classification
Fungi :
• They belong to
the vegetable
kingdom and
are structurally
very complex
e.g. Ringworm
Protozoa :
• Unicellular
members of the
animal
kingdom. Their
size is
extremely
variable e.g..
E. histolytica,
G. Lamblia,
T.Vaginalis
Viruses :
• Smallest micro-
organisms,
requires
electronic
microscope for
visualization
Rickettsia :
• Intermediary
form between
bacteria and
viruses
Bacteria :
• Larger than
viruses and
rickettsia. They
are small
simple and
unicellular and
may vary in
size from 2 to 5
microns.
Reproduction is
by simple
binary fission.
One single
bacteria can
produce 17
million bacteria
in 24 hour

5. Bacteria
Single-celled organisms that multiply by cell division and can cause
numerous disease in humans.
Classification
Based on Atmospheric tolerance, they are classified as:-
1. Aerobic:
Able to live and grow in presence of atmospheric oxygen
2. Anaerobic:
Able to live and grow in the absence of atmospheric oxygen.
They require reduced or no oxygen for growth.
They exist as normal flora on the mucosal surface. The major sites are Mouth,
GI Tract, Skin and Female Genital Tract

6. Classification
Based upon
staining of
the
Bacterial
cell
membrane
Gram Positive: eg. Staph. Aureus, Streptococcus Pneumoniae,
Gram Negative: eg. Haemophilus Influenzae,
Atypical: Do not stain with gram stain. Chlamydia Pneumoniae,
Legionella Pneumoniae
Acid Fast: Type of atypical bacteria. Mycobacterium Tuberculosis
Based upon
shape of
cells, Most
bacteria are
of 3 shapes:
Cocci- round
Bacilli- rod
Spirilli- spiral shaped

7. •An antibiotic is a chemical substance produced by various species of
microorganisms that is capable in small concentrations of inhibiting the growth
of other microorganisms
Old:
•An antibiotic is a product produced by a microorganism or a similar substance
produced wholly or partially by chemical synthesis, which in low
concentrations, inhibits the growth of other microorganisms. They are the
agents which either kill or inhibit the growth of bacteria through various
mechanisms.
Updated:
Definitions of Antibiotics

8. Classification of Antibiotics
• Inhibit cell wall synthesis (Penicillin's/Cephalosporin's)
• Inhibit protein synthesis (Tetracycline's/ Erythromycin)
• Inhibit DNA synthesis (Fluor quinolones)
Based on MOA:
• Narrow: Penicillin, Streptomycin
• Broad: Tetracycline's, Chloramphenicol
Based on Spectrum of Activity:
• Bacteriostatic: Tetracycline's, Erythromycin
• Bactericidal: Penicillin, Ciprofloxacin
Based on Type of action:

9. Antibiotics Classification

10. Classification of Antibiotics
• Antibacterial agent which kills the bacteria usually when
they are in the process of multiplication e.g. Penicillin,
Cefadroxil, Cefuroxime,Ciprofloxacin.
Bactericidal
• Antibacterial agent which inhibits the growth of bacteria
e.g. Tetracycline.
Bacteriostatic

11. Antibiotics Classification