Antibiotics, Biotechnology, Microbiology, Immunology

1. Antibiotics
By
Assist.Prof
Berciyal Golda. P
VICAS

2. INTRODUCTION
Antibiotics, also known as anti-bacterials, are
medications that destroy or slow down the growth of bacteria.
They include a range of powerful drugs and are used to treat
diseases caused by bacteria.
Antibiotics cannot treat viral infections, such as cold,
flu, and most coughs.
Antibiotics cannot treat viral infections, such as cold,
flu, and most coughs.
Various families of antibiotics are used for various types
of microorganisms to achieve control and assist body defenses
during times of infection.

3. Antibiotics are products of microorganisms that react
with and inhibit the growth of other microorganisms.
An antibiotic should be selectively toxic to pathogenic
microorganisms, should not incite an allergic response in the body,
should not upset the normal microbial population of various body
sites, and should not foster the development of drug resistance.
Antibiotics are Substances derived from a
microorganism or produced synthetically (Sulfonamides &
Quinolones) to kill or suppress the growth of
other microorganisms.

4. Definition
The word “antibiotics” comes from the Greek ,
Anti- “against”& bios “life”.
“Antibiotic” is from antibiosis, meaning against life
Antimicrobial agents are chemical substances
that can either kill or inhibit the growth of
micro-organism that may be natural products or
synthetic chemicals”.It may be
Anti-bacterial
Anti-viral
Anti-fungal
Anti-parasitic

5. HISTORY
 In 1928, Sir Alexander Fleming, a Scottish biologist, observed that
Penicillium notatum, a common mold, had destroyed staphylococcus
bacteria in culture, that was left uncovered accidentally.
 Penicillin was isolated in 1939,and in 1944 Selman and Albert
American Microbiologist , isolated Streptomycin & a number of other
antibiotics.
Sir Alexander Fleming
Fleming’s Petri Dish

6. Classification of Antibiotics
Antibiotics are classified by several
ways:
• On the basis of mechanism of action
• On the basis of spectrum of activity
• On the basis of mode of action

7. Mechanism of action of antimicrobial agents
1. Inhibition of cell wall synthesis:
• Penicillins, Cephalosporins, Bacitracin & Vancomycin
2. Inhibition of functions of cellular membrane:
• Polymyxins
3. Inhibition of protein synthesis:
• Chloramphenicol, Macrolides & Clindamycin
• Tetracyclines & Aminoglycosides
4. Inhibition of nucleic acid synthesis:
• Quinolones
• Rifampin
5. Inhibition of folic acid synthesis:
• Sulfonamides & trimethoprim

8. 1.On the basis of mechanism of action

9. 2. On the basis of spectrum of activity

10. Antimicrobial Spectrum
Antimicrobial spectrum: the scope that a drug
kills or suppresses the growth of
microorganisms.
Narrow-spectrum: The drugs that only act on one
kind or one strain of bacteria.(Isoniazide)
Broad-spectrum: The drugs that have a
wide antimicrobial scope.(Tetracycline
& Chloramphenicol)

11. 3.On the basis of mode of action
• Tetracycline
• Chloramphenicol
• Erythromycin
• Lincomycin
Bacteriostatic
antibiotics:
• Cephalosporin
• Penicillin
• Erythromycin
• Aminoglycosides
• Cotrimoxazole
Bacteriocidal
antibiotics:

12. Misuse of Antibiotics
Antibiotic misuse, sometimes called antibiotic
abuse or antibiotic overuse
The misuse or overuse of antibiotics, may
produce serious effects on health.
It is a contributing factor to the creation of
multidrug- resistant bacteria, informally called
“super bugs”.

13. Antibiotic Resistances and Cross
Resistances
Antibiotic resistance is the phenomenon that
susceptibility of pathogenic microorganisms to
antibiotic becomes lower or even loses after the
microorganisms contact with antibiotic many times.
When the bacteria show resistance to one
antibiotic, they are also resistant to some other
antibiotics. This phenomenon is called cross antibiotic
resistance.

14. Mechanisms of Antibiotic Resistance
1. Alteration of the target site of the antibiotic
• One of the most problematic antibiotic resistances
worldwide, methicillin resistance among Staphylococcus
aureus
2. Enzyme inactivation of the antibiotic
• β-lactam antibiotics (Penicillins & Cephalosporins) can be
inactivated by β-lactamases.

15. 3.Active transport of the antibiotic out of the
bacterial cell
• Active transport of the antibiotic out of the bacterial cell
(efflux pumps) as removal of some antibiotics e.g.
Tetracyclines, Macrolides & Quinolones
4.Decreased permeability of the bacterial cell wall
to the antibiotic
• Alteration in the porin proteins that form channels in the cell
membrane e.g. Resistance of Pseudomonas aeruginosa to a
variety of Penicillins & Cephalosporins

17. Uses of Antibiotics
Today, the name antibiotic is synonymous for drugs that kill
bacteria. And because of this, mortality rates have reduced and lifespan has
increased.
These microbial infections can wipe out an entire population of
organisms and that can adversely affect the ecosystem. For instance,
anthrax is a disease that infects livestock and can spread to humans, which
is often fatal unless it is treated.
Antimicrobial therapy is used to destroy or to prevent the
microorganism’s growth. However, it might not stop the damage that is
already done.
For example, the anthrax-causing bacterium Bacillus anthracis
does not actually kill the host, instead, it is the toxins which are produced
that does the deed.
Antibiotics might kill the bacteria, but the toxins remain in the
body and continue to cause damage.

18. General Principles of Antimicrobial
Therapy
• Identification of the infecting organism should precede
antimicrobial therapy when possible.
 The pathogenic microorganism susceptibility to antimicrobial
agents should be determined, if a suitable test exists.
 Factors that influence the choice of an antimicrobial agent or its
dosage for a patient include the age, renal & hepatic function,
pregnancy status and the site of infection, etc.
Two types of antimicrobial therapies are available:
•Microbicidal therapy – It is used to kill the microorganisms.
•Microbiostatic therapy – It is used to prevent microorganism
growth.

19. 1. Microbicidal therapy –
It is used to kill the microorganisms Submerged electrical
discharges between copper-containing electrodes rendered the
treated liquid microbicidal. Part of this activity was unstable
and decreased rapidly during the first few minutes. ... The
stable microbicidal activity was due to copper released from
the electrodes.
2. Microbiostatic therapy –
It is used to prevent microorganism growth.
It reversibly inhibits growth.
Bacteriostats are often used in plastics to prevent growth of
bacteria on surfaces. Bacteriostats commonly used in
laboratory work include sodium azide (which is acutely toxic)
and thiomersal.

20. Bacteriostatic antibiotics limit the growth of bacteria by
interfering with
bacterial protein production, DNA replication, or other
aspects of bacterial cellular metabolism
They must work together with the immune system to remove the
microorganisms from the body.
However, there is not always a precise distinction between them
and bactericidal antibiotics; high concentrations of some
bacteriostatic agents are also bactericidal, whereas low
concentrations of some bactericidal agents are bacteriostatic.

21. Modeof Action
Different antibiotics have different modes of action, owing to the
nature of their structure and degree of affinity to certain target
sites within bacterial cells.
1.Inhibitors of cell wall synthesis.
While the cells of humans and animals do not have cell
walls, this structure is critical for the life and survival of bacterial
species.
A drug that targets cell walls can therefore selectively kill
or inhibit bacterial organisms.
Examples: penicllins, cephalosporins, bacitracin and vancomycin.

22. 2. Inhibitors of cell membrane function.
Cell membranes are important barriers that segregate
and regulate the intra- and extracellular flow of substances.
A disruption or damage to this structure could result in
leakage of important solutes essential for the cell’s survival.
Because this structure is found in both eukaryotic and
prokaryotic cells, the action of this class of antibiotic are often
poorly selective and can often be toxic for systemic use in the
mammalian host.
Most clinical usage is therefore limited to topical
applications.
Examples: polymixin B and colistin.

23. 3.Inhibitors of protein synthesis.
Enzymes and cellular structures are primarily made of
proteins. Protein synthesis is an essential process necessary for
the multiplication and survival of all bacterial cells.
Several types of antibacterial agents target bacterial
protein synthesis by binding to either the 30S or 50S subunits of
the intracellular ribosomes.
This activity then results in the disruption of the normal
cellular metabolism of the bacteria, and consequently leads to the
death of the organism or the inhibition of its growth and
multiplication.
Examples: Aminoglycosides, macrolides, lincosamides,
streptogramins, chloramphenicol, tetracyclines.

24. 4. Inhibitors of nucleic acid synthesis.
DNA and RNA are keys to the replication of all living
forms, including bacteria.
Some antibiotics work by binding to components involved
in the process of DNA or RNA synthesis, which causes
interference of the normal cellular processes which will ultimately
compromise bacterial multiplication and survival.
Examples: quinolones, metronidazole, and rifampin.

25. 5. Inhibitors of other metabolic processes.
Other antibiotics act on selected cellular processes essential
for the survival of the bacterial pathogens.
For example, both sulfonamides and trimethoprim disrupt
the folic acid pathway, which is a necessary step for bacteria to
produce precursors important for DNA synthesis.
Sulfonamides target and bind to dihydropteroate synthase,
trimethophrim inhibit dihydrofolate reductase; both of these
enzymes are essential for the production of folic acid, a vitamin
synthesized by bacteria, but not humans.

27. Complications of Antibiotic Therapy
• Resistance due to inappropriate use of antibiotics
• Hypersensitivity (Penicillin)
• Direct toxicity (Aminoglycosides = ototoxicity)
• Super infections (broad spectrum antimicrobials cause
alteration of the normal flora; often difficult to treat)