This document discusses antimicrobial drugs, including antibiotics. It defines antibiotics as substances produced by microorganisms that inhibit other microbes. It lists several antibiotic-producing microbes such as Bacillus, Penicillium, Streptomyces, and Micromonospora. The document also discusses the mechanisms of action of antimicrobials including inhibition of cell wall synthesis, protein synthesis, and nucleic acid synthesis. It provides examples of antimicrobials that act through these mechanisms like penicillin, tetracyclines, and rifampin. Finally, it notes some safety concerns with antimicrobial use like toxicity, interactions, resistance, and effects on normal flora.

1. Antimicrobial Drugs
 Chemotherapy: The use of drugs to treat a disease
 Antimicrobial drugs: Interfere with the growth of
microbes within a host
 Antibiotic: A substance produced by a microbe that,
in small amounts, inhibits another microbe
 Selective toxicity: A drug that kills harmful microbes
without damaging the host

2. Microbial Sources of Antibiotics

3. Antibiotic Spectrum of Activity

4. Antimicrobial Drugs:
Antibiotic: Substance produced by a microorganism that in
small amounts inhibits the growth of another microbe.
Antibiotic producing microbes include:
Gram-Positive Rods:
 Bacillus subtilis: Bacitracin
 Bacillus polymyxa: Polymyxin
Fungi
 Penicillium notatum: Penicillin
 Cephalosporium spp.: Cephalothin
Actinomycetes:
 Streptomyces venezuelae: Chloramphenicol
 Streptomyces griseus: Streptomycin
 Streptomyces nodosus: Amphotericin B
 Micromonospora purpurea: Gentamycin

5. • Antibacterials: Relatively easy to develop and find with
low toxicity because procaryotic cells are very different
from host cells.
• Antihelminthic, antiprotozoan, and antifungal drugs:
More difficult to develop because eucaryotic cells resemble
human cells.
• Antivirals: Most difficult to develop because virus
reproduces using host cell enzymes and machinery.
Spectrum of Antimicrobial Activity
Broad Spectrum: Effective against many different types
of bacteria (e.g.: both gram positive and negative).
Examples: Tetracyclin
 Narrow Spectrum Antibiotics: Effective against a
subset of bacteria (either gram positive and negative).
Examples: Penicillin, Isoniazid (Mycobacteria only}

6. Mechanisms of Antimicrobial
Action
 Bacteria have their own enzymes for
 Cell wall formation
 Protein synthesis
 DNA replication
 RNA synthesis
 Synthesis of essential metabolites
 Viruses use host enzymes inside host cells
 Fungi and protozoa have own eukaryotic enzymes
 The more similar the pathogen and host enzymes, the
more side effects the antimicrobials will have

7. The Action of Antimicrobial Drugs
 Bactericidal
 Kill microbes directly
 Bacteriostatic
 Prevent microbes from growing

8. The Action of Antimicrobial Drugs

9. Antimicrobial Mechanisms of Action
 Inhibition of Cell Wall Synthesis: Interfere with
peptidoglycan synthesis.
 Result in cell lysis.
 Low toxicity.
 E.g.: Penicillin and vancomycin.
Other antibiotics in the penicillin family (B-lactams):
Ampicillin, Methicillin, and Oxacillin

10. Antimicrobial Mechanisms of Action
Inhibition of Protein Synthesis: Interfere with
procaryotic (70S) ribosomes, also found in
mitochondria.
 Most have broad spectrum of activity
 Tetracyclin, chloramphenicol, erythromycin, and
streptomycin.

11. Antimicrobial Mechanisms of Action
 Injury to the Plasma Membrane: Cause changes in
membrane permeability.
 Result in loss of metabolites and/or cell lysis.
 Many polypeptide antibiotics.
 E.g.: Polymyxin B (antibacterial) or miconazole
(antifungal).
 Inhibition of Nucleic Acid (DNA/RNA) Synthesis:
Interfere with DNA replication and transcription.
 May be toxic to human cells.
 E.g.: Rifampin and quinolones

12. Antimicrobial Mechanisms of Action
 Inhibition of Synthesis of Essential Metabolites:
Involve competitive inhibition of key enzymes.
 Closely resemble substrate of enzyme.
 E.g.: Sulfa drugs inhibit the synthesis of folic acid which is
necessary for DNA and RNA synthesis.

13. Inhibitors of Cell Wall Synthesis
 Antibiotics effective against Mycobacteria:
interfere with mycolic acid synthesis or
incorporation. This process inhibits the
synthesis of mycolic acid which required
for themycobactericidalbacterial cell wall.
Isoniazid is to rapidly-
dividing mycobacteria but
is bacteriostatic if the mycobacterium is
slow-growing

14. Isoniazid may cause side effects:
 diarrhea
 vision problems
 eye pain
 numbness or tingling in the hands and feet
 skin rash
 fever
 swollen glands
 sore throat
 unusual bleeding or bruising
 stomach pains or tenderness

15. Sulfonamides
 AKA “sulfa drugs”
 Effective against a broad range of microorganisms
 Block specific step in biosynthetic pathway of folic
acid
 Interfere with PABA and folic acid formation, thereby
destroying bacteria

16. Competitive Inhibitors
 Sulfonamides
(sulfa drugs)
 Inhibit folic acid synthesis
 Broad spectrum

17. Competitive Inhibitors

19. Sulfonamides’ Side Effects
 Rash
 Nausea
 Drug fever
 Vomiting
 Jaundice
 Blood complications
 Kidney damage

20. Criteria for the evaluation of
quality of antimicrobial drug use

21. Safety Concerns with the Use of Antimicrobials:
 Toxicity
 Kidney damage
 Liver damage
 Bone marrow (Chloramphenicol and aplastic anemia)
 Interactions with other medications
 May neutralize effectiveness of contraceptive pills
 Hypersensitivity reactions
 Anaphylactic reactions to penicillin
 Triple antibiotic ointment (rashes & neomycin B)
 Fetal damage/risk to pregnant women
 Tetracyclin causes discoloration of teeth in children and may cause liver
damage in pregnant women
 Fluoroquinolones may cause cartilage damage.
 Dysbiosis: Host’s normal beneficial flora killed off, causing various
symptoms such as diarrhea, digestive problems (constipation, gas),
yeast infections, etc. Probiotics and antifungals can help.
 Antibiotic Resistance: Multiple antibiotic resistant is becoming a
huge problem. MRSA= Methicillin Resistant Staphylococcus aureus.