This document discusses antimicrobial agents and their classification and mechanisms of action. It describes how antibiotics can be classified based on their spectrum of activity, source, or mechanism. The main mechanisms discussed are inhibition of cell wall synthesis, disruption of cell membranes, inhibition of protein synthesis through effects on ribosomes, inhibition of DNA, RNA or folic acid synthesis. Factors leading to drug resistance and mechanisms of acquired resistance such as efflux pumps, target site mutations and enzymatic inactivation are also summarized.

1. Antimicrobial Agents
MC3: Microbiology and Parasitology
University of Saint Anthony
College of Healthcare Education

2. OVERVIEW
Antimicrobials

3. OVERVIEW
Antibiotics

4. CHARACTERISTICS
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5. CHARACTERISTICS
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6. CHARACTERISTICS
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7. SOURCES OF ANTIBIOTICS
Natural Semi-synthetic Synthetic

8. CLASSIFICATION: Based of Spectrum Activity

9. CLASSIFICATION: Based on their Antimicrobial Activity

10. CLASSIFICATION: Based on their Mechanism

12. Beta-lactam antibiotics
(penicillin-binding proteins)
act by inhibiting the conversion of
immature peptidoglycan to mature
peptidoglycan by directly inhibiting
bacterial transpeptidases

13. Glycopeptides antibiotics
interfere with cell wall synthesis, which
are composed of glycosylated cyclic or
polycyclic non-ribosomal peptides

14. CLASSIFICATION: Based on their Mechanism

15. Agents that target the cell
membrane are classified into
• Cationic Agents
• Anionic Agents
• Neutral Agents

16. Polymyxins
After binding to lipopolysaccharide (LPS)
in the outer membrane of gram-negative
bacteria disrupt both the outer and inner
membranes

17. Gramicidin
bactericidal activity is a result of increasing
the permeability of the bacterial cell
membrane; is active against gram?positive
bacteria, except for gram-positive bacilli, and
against selective gram-negative organisms,
such as Neisseria bacteria

18. Polyenes (Antifungal Drug)
alter the permeability of the cell
membrane

19. Azoles
interfere with the synthesis of
ergosterol, a major component of
fungal membrane

20. CLASSIFICATION: Based on their Mechanism

22. Inhibitors of the 30S ribosomal sub unit
interfere primarily with the initiation
process

23. Inhibitors of the 30S ribosomal sub unit
interfere primarily with the initiation
process
Aminoglycosides
⚬ cause formation of non?functional
complexes and misreading

24. Inhibitors of the 30S ribosomal sub unit
interfere primarily with the initiation
process
Spectinomycin
⚬ related to aminoglycosides that
binds to a protein in a 30S ribosomes
different from target of the
aminoglycosides

25. Inhibitors of the 30S ribosomal sub unit
interfere primarily with the initiation
process
Tetracycline
⚬ targets bacterial 30S ribosomal
subunit

26. Agents that bind to the 50S ribosomal sub-
unit are the inhibitors of elongation process
of protein synthesis

27. Agents that bind to the 50S ribosomal sub-
unit are the inhibitors of elongation process
of protein synthesis
Chloramphenicol
⚬ acts by binding a peptidyl
transferase enzyme thereby
inhibiting peptide bond formation

28. Agents that bind to the 50S ribosomal sub-
unit are the inhibitors of elongation process
of protein synthesis
Macrolides
⚬ act peptidyl transferase by
interfering with its reaction or
translocation

29. Agents that bind to the 50S ribosomal sub-
unit are the inhibitors of elongation process
of protein synthesis
Lincinoids
⚬ clindamycin is important and it has
similar target as macrolides.

30. CLASSIFICATION: Based on their Mechanism

31. Agents that inhibit DNA
topoisomerases
among the different antimicrobial
agents, quinolones (First gen: nalidixic
acid and oxolinic acid/ Newer gen:
fluoroquinolones) is the most effective
against DNA gyrase.

32. Agents that inhibit RNA
synthesis
are agents that act by interfering
with the B?subunit of an RNA
polymerase that is needed for RNA
synthesis. (Rifampicin)

33. CLASSIFICATION: Based on their Mechanism

35. Trimethoprim and sulfonamides
⚬ are antibiotics that interfere with
folic acid metabolism; act as
competitive inhibitors of
tetrahydrofolic acid

36. Sulfonamides
⚬ act specifically by inhibiting
formation of dihydrofolic acid

37. Trimethoprin
⚬ inhibits formation of tetrahydrofolic
acid by inhibiting the enzyme
dihydrofolate reductase

38. MECHANISM OF DRUG
RESISTANCE

39. MECHANISM OF DRUG RESISTANCE

40. FACTORS
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41. FACTORS
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42. RESISTANCE ACQUIRED THROUGH GENETIC
EXCHANGE CAN OCCUR THREE WAYS
Transformation Transduction Drug
Modification or
Inactivation

43. RESISTANCE ACQUIRED THROUGH GENETIC
EXCHANGE CAN OCCUR THREE WAYS
Prevention of
Cellular Uptake or
Efflux
Modification of
Target Sites
Overproduction
or Bypass of
Target Enzyme

44. RESISTANCE ACQUIRED THROUGH GENETIC
EXCHANGE CAN OCCUR THREE WAYS
Target Mimicry