This document discusses principles of antimicrobial agents and antibiotics. It defines antimicrobial agents and antibiotics, and outlines ideal qualities such as killing pathogens without harming the host. Antibiotics can be natural, derived from fungi or bacteria, or synthetic. Terms like bacteriostatic, bactericidal, and synergistic effects are explained. The document also covers antibiotic resistance, mechanisms by which it occurs, and risks that can lead to resistance. Consequences of antibiotic resistance and measures to combat it are described. Finally, antibiotics are classified based on their activity, spectrum, absorption, and mechanism of action.

1. Principle of Antimicrobial
Agents and Antibiotics
By
Pharm BAHATI Abdallah

2. Introduction
• Antimicrobial Agent
any chemical or drug used to treat an infectious disease, either
by inhibiting or killing the pathogens in vivo.
And,
• Antibiotic
Substances derived from a microorganism or produced synthetically,
that in low concentration/dose destroys or limits the growth of a living
organism.

3. Ideal qualities for Antimicrobial
Agent/Antibiotic
1. kill or inhibit the growth of pathogens
2. cause no damage to the host
3. cause no allergic reaction to the host
4. stable when stored in solid or liquid form
5. remain in specific tissues in the body long enough to be effective
6. kill the pathogens before they mutate and become resistant to it

4. Antibiotic Sources
1. Natural
a.Fungi – penicillin, griseofulvin
b.Bacteria – Bacillus sp. (polymixin, bacitracin) Actinomycetes
(tetracycline, chloramphenicol, streptomycin)
2. Synthetic
-Most are semisynthetic like Ampicillin,Norfloxacin etc

5. General terms in Antibiotics
• Bacteriostatic means a chemical agent that stop bacterial growth
but not necessarily kill them.
• Bacteriocidal means a chemical agent that stops bacterial growth
by killing them.
• Synergistic effect means arising of two or more drugs that
produce the effect greater than the sum of their individual effects,
it is opposite to Antagonism.
• Additive effect arising of two or more drugs that produce the
same effect as the sum of their individual effects.
• Selective toxicity ability of the drug to kill or inhibit the bacterial
growth without harming the host.

6. Antibiotic Resistance
• The ability of the bacteria or other microorganisms to
reduce or eliminate the effectiveness of a drug (antibiotic)
to which they were once sensitive.
• The pathogenic microorganisms continue to survive and
cause more harm to the host.
• The Antibiotic Resistance is now the major concern of
overuse of antibiotics inappropriately.

7. Mechanisms for Drug resistance Occurance
1
1. Production of enzymes that inactivate the drug
α. β-lactamase
S. aureus, Enterobacteriaceae, Pseudomonas, H. influenza
a. Chloramphenicol acetyltransferase
S. aureus, Enterobacteriaceae
a. Adenylating, phosphorylating or acetylating
enzymes (aminoglycosides)
S. aureus, Strep, Enterobacteriaceae, Pseudomonas

8. 2
2. Altered permeability to the drug
result to decreased effective intracellular concentration
Eg in Tetracycline, Penicillin, Polymixins, Aminoglycosides,
Sulfonamides
3. Synthesis of altered structural targets for the drug
Streptomycin resistance – mutant protein in 30S ribosomal subunit →
delete binding site →Enterobacteriaceae
Erythromycin resistance – altered receptor on 50S subunit due to
methylation of a 23S rRNA → S. aureus

9. 3
4. Altered metabolic pathway that bypasses the
reaction inhibited by the drug
Sulfonamide resistance – utilize preformed folic acid instead of
extracellular PABA → S.aureus, Enterobacteriaceae
5. Multi-drug resistance pump
Bacteria actively export substances including
drugs in exchange for protons
Quinolone resistance

10. Risk attributes for existance of Drug
Resistance 1
• Prescription not taken correctly
• Antibiotics sold without medical supervision
• Spread of resistant microbes in hospitals due to lack of
hygiene
• Lack of quality control in manufacture or outdated
antimicrobial

11. 2
• Inadequate surveillance or defective susceptibility assays
• Poverty or war
• Use of antibiotics in foods
-Antibiotics are used in animal feeds and sprayed on plants
to prevent infection and promote growth
-Multi drug-resistant Salmonella typhi has been found in 4
states in 18 people who ate beef fed antibiotics

12. Consequences of AR
• Infections resistant to available antibiotics
• Increased cost of treatment
• Increased in morbidity and mortality rate

13. Measures to combat AR
• Speed development of new antibiotics
• Track resistance data nationwide
• Restrict IMPROPER antimicrobial use
• Direct observed dosing (TB)
• Use more narrow spectrum antibiotics
eg older penicillins (Pen G) and the Macrolide
(Erthromycin)
• Use antimicrobial cocktails/ combination therapy

14. Classification of Antibiotics 1
I. According to antimicrobial activity
Bactericidal
Bacteriostatic
II. According to bacterial spectrum of activity
Narrow spectrum
Broad spectrum
III. According to absorbability from the site of
administration to attain significant concentration for the
treatment of systemic infection
Locally acting

15. 2
IV. According to mechanism of action
Inhibit bacterial cell wall synthesis
Alter the function and permeability of the cell membrane
Inhibit protein synthesis (translation and transcription)
Inhibit nucleic acid synthesis

16. END