Antimicrobial agents and chemotherapy

1. Abdulqani Ahmed Muhumed ID: 2032
Individual assignment
Pro: Aidarous Mohamed
Course; Microbiology

3. Objectives
1. Introduction & Historical background
2. Antimicrobial agents
3. Chemotherapy
4. Classification of antimicrobial agents
5. Mechanisms of Action of Antimicrobial agents
6. General characteristics of antimicrobial drugs
7. Difference b/w Antimicrobial agents & Chemotherapy
8. Conclusion

4. Introduction & Historical background
• Drugs have been used for the treatment of infectious diseases since
the 17th century (e.g quinine for malaria, emetine for amebiasis);
however, chemotherapy as a science began in the first decade of the
20th century with understanding of the principles of selective
toxicity, the specific chemical relationships between microbial
pathogens and drugs, the development of drug resistance, and the
role of combined therapy.
• The first planned chemotherapy was arsphenamines for syphilis.

5. Antimicrobial agents
• An antimicrobial is an agent that kills microorganisms or stops
their growth.
• The use of antimicrobial medicines to treat infection is known
as antimicrobial chemotherapy .
• while the use of antimicrobial medicines to prevent infection is
known as antimicrobial prophylaxis.

6. Chemotherapy
• Chemotherapy (chemo) is a type of treatment that includes a
medication or combination of medications to treat cancer.
• The goal of chemo is to stop or slow the growth of cancer cells.
Chemo is considered a systemic therapy ( this means it may affect
your entire body ) .
• Chemo medications attack rapidly growing cancer cells, but they can
also affect healthy cells that grow rapidly. The effect of these
medications on normal cells often causes chemo side effects.

7. Classification of antimicrobial agents
• Antimicrobial medicines can be grouped according to the
microorganisms they act primarily against. For example
antibiotics are used against bacteria and antifungals are used
against fungi.
• They can also be classified according to their function. Agents
that kill microbes are called microbicidal, while those that
merely inhibit their growth are called biostatic.

8. Classification of antimicrobial agents
1. Anti-bacterial
2. Anti-fungal
3. Anti-viral
4. Anti-parasitic

9. Classification of antimicrobial agents
1. Antibacterial:- is a type of antimicrobial substance active
against bacteria ; Prolonged use of certain antibacterials can decrease the
number of gut flora, which may have a negative impact on health.
Also called antibiotics and have two types Bactericidal & Bacteriostatic .

10. Classification of antimicrobial agents
 Bactericidal: antibiotics kill bacteria directly .
The antibiotic polymyxin B injures the plasma membrane of bacteria,
allowing their contents to leak out. Under normal circumstances, bacteria
and other cells have to keep a perfect balance of ions on both sides of the
plasma membrane because of osmosis. Polymyxin B disrupts this balance,
and also lets other important molecules, like DNA and RNA, leak out, so the
bacterium is a goner.

11. Classification of antimicrobial agents
 Bacteriostatic: bacteriostatic antibiotics stop bacteria from growing.
how do bacteriostatic antibiotics help clear up an infection, if they don't
actually kill bacteria? Well, bacteria normally divide really quickly in our
bodies, and their numbers can get totally out of control. But if an antibiotic
stops them from growing and dividing, the host's immune system will be
able to get rid of the bacteria. E.g Tetracycline

12. Classification of antimicrobial agents
2. Anti-fungal : are used to kill or prevent further growth of fungi. In
medicine, they are used as a treatment for infections such as athlete's
foot, ringworm and thrush and work by exploiting differences between
mammalian and fungal cells. They kill off the fungal organism without
dangerous effects on the host. Unlike bacteria, both fungi and humans
are eukaryotes. Thus, fungal and human cells are similar at the molecular
level, making it more difficult to find a target for an antifungal drug to attack
that does not also exist in the infected organism. Consequently, there are
often side effects to some of these drugs.

13. Classification of antimicrobial agents
3. Antivirals :Antiviral drugs are a class of medication used specifically for
treating viral infections. Like antibiotics, specific antivirals are used for
specific viruses. They are relatively harmless to the host and therefore can be
used to treat infections. They should be distinguished from viricides, which
actively deactivate virus particles outside the body.
Many antiviral drugs are designed to treat infections by retroviruses,
mostly HIV.

14. Classification of antimicrobial agents
• 4. Antiparasitics : Antiparasitics are a class of medications indicated for
the treatment of infection by parasites, such
as nematodes, cestodes, trematodes, infectious protozoa, and amoebae.
Like all antimicrobials against intracellular microbes, they must kill the
infecting pest without serious damage to the host. Have two types
Antiprotozoal agent & Anti-helminthic agents/ Anthelmintics.

15. Mechanisms of Action of Antimicrobial agents
• They are classified as follows:
I. Inhibition of cell wall synthesis.
II. Inhibition of cell membrane function, e.g., alteration of cell membrane
permeability or inhibition of active transcription.
III. Inhibition of protein synthesis, i.e., inhibit translation and
transcription.
IV. Inhibition of nucleic acid synthesis.

16. Ι. Drugs that inhibit cell wall synthesis
“Peptidoglycan synthesis’’
1-Penicillins
2-Cephalosporins cell wall
synthesis ''Peptidoglycan
synthesis'':-
They act by damaging the
plasma membrane, i.e., inhibit
early steps in the biosynthesis of
peptidoglycan.
3-Bactracin
4-Vancomycin
5-Ristocetin
They act by blocking the peptidoglycan by
inhibition of transpeptidation, i.e., blocking the
cross linking of peptidoglycan.
6-Novobiocin
7-Cycloserine:- It act by inhibition of incorporation of D-alanine into
peptidoglycan of bacterial cell wall by blocking alanine racemase enzyme.

17. Ι. Drugs that inhibit cell wall synthesis
“Peptidoglycan synthesis’’
*Cycloserine act as analoge to D-alanine.
The difference is susceptibility of G+ve and G-ve bacteria to
penicillins or cephalosporins depends or structural difference in
their cell wall
a-amount of peptidoglycan
b-Presence of receptors
c-lipid nature of cross linking
d-activity of autolytic enzymes.

18. II. Drugs that inhibit cell membrane
function:-
1-Polymyxins:- It act by binding to membrane rich in phosotidyl
ethanolamine leading to disruption of cell membrane. (This action is
similar to that cationic detergents).
2-Polyene Antibiotics (A , Amphotericin B, Nystatin):- The act by binding to
membrane sterol.
3-Imidazoles:- They act by preventing the biosynthesis of the membrane
lipid.

19. III. Drugs that inhibit protein synthesis:-
1-Aminoglycoside antibiotics
2-Tetracyclines antibiotics.
3-Spectinomycin antibiotics.
They act by binding to the
30s subunit of bacterial
ribosome's.
* The aminglycosides include gentamicin, neomycin,
kanamycin, streptomycin, tobramycin, netilmycin, and amikacin.
4-Macrolides (erythromycin, oleandomycin)
5-Lincomycin and clindamycin.
They act by binding to
50s subunit of bacterial
ribosomes.

20. IV. Drugs that inhibit nucleic acid synthesis:-
A – drugs that inhibit DNA synthesis:-
1- Actinomycin:- it act by formation of complex with DNA.
2- Mitomycin:- it act by blocking DNA replication.
3- Sulfonamides:- they act by inhibition of the formation of folic acid
from P-amino benzoic acid(PABA) by competition with PABA, i.e.,
inhibition of folate metabolism.
4-Trimethoprim:- it act by inhibition of dihydrofolate reductase.
5- Isoniazid:- act by compete with pyridoxine.
*Isoniazid = Iso nicotinic acid hydrazid (INH).
* Actinomycin and Mitomycin are not used for treatment of
infection , but inhibit bacterial and animal cells.

21. IV. Drugs that inhibit nucleic acid synthesis:-
• 6-Quinolones (Nalidixic acid, oxolinic acid):-
They act by blocking DNA gyrase (Topoisomerase II )
Inhibition of DNA synthesis
B – Drugs inhibit RNA synthesis:-
*Rifampicin:- It inhibits RNA synthesis by blocking the RNA
polymerase.

22. General characteristics of antimicrobial drugs
A. Selective toxicity – agent must kill or inhibit microbe while damaging the
host as little as possible
1. balance between the
a) therapeutic dose – drug level required for therapeutic treatment of an
infection
b) toxic dose – drug level that is toxic to host

23. General characteristics of antimicrobial drugs
2. therapeutic index – ratio of toxic dose to therapeutic dose (larger the number =
better)
B. Range of effectiveness
1. Narrow-spectrum: active against specific G+ve and G-ve bacteria .
2. Broad-spectrum: are antibiotics that are active against many Gram-
positive and Gram-negative bacteria.
C. Classes based on target organisms that it effects
D. Cidal vs. static

24. Difference b/w Antimicrobial agents & Chemotherapy
• An antimicrobial agent is a substance that kills or inhibits the growth of microbes
such as bacteria, fungi, protozoals or viruses. Antimicrobial drugs either kill
microbes (microbicidal) or prevent the growth of microbes (microbistatic).
Disinfectants are anti-microbial substances used on non-living objects.
• A chemotherapeutic agent acts by killing cells that divide rapidly, one of the
main properties of cancer cells. This means that it also harms cells that divide
rapidly under normal circumstances: cells in the bone marrow, digestive tract and
hair follicles; this results in the most common side-effects of chemotherapy–
myelosuppression (decreased production of blood cells), mucositis (inflammation
of the lining of the digestive tract) and alopecia (hair loss).

25. Conclusion
• Adequate knowledge of various antimicrobial classification,mechanisms of
action are crucial in optimal patients care and in prevention of resistance.
• Many types of antimicrobial agents with different mechanisms of action,
pharmacological properties and spectra of activity are available.
• Use of antimicrobial chemotherapy should be tailored to individual cases, with a
good understanding of each drug’s characteristics.
• It should be recognised that antimicrobialchemotherapy has potential negative
effects including adverse ones.