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Questions and Answers
What is the goal of antimicrobial chemotherapy?
What is the goal of antimicrobial chemotherapy?
To administer a drug to an infected person that destroys the infective agent without harming the host’s cells.
Which of the following characteristics describes an ideal antimicrobial drug? (Select all that apply)
Which of the following characteristics describes an ideal antimicrobial drug? (Select all that apply)
Antibiotics are produced only by bacteria.
Antibiotics are produced only by bacteria.
False
From which bacterial genera are many antibiotics derived?
From which bacterial genera are many antibiotics derived?
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Match the following microbial sources with their antibiotic products:
Match the following microbial sources with their antibiotic products:
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The term for any chemical used in the treatment, relief, or prophylaxis of a disease is called a ______.
The term for any chemical used in the treatment, relief, or prophylaxis of a disease is called a ______.
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What are semisynthetic drugs?
What are semisynthetic drugs?
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Narrow-spectrum drugs are effective against a wide range of microbial types.
Narrow-spectrum drugs are effective against a wide range of microbial types.
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What are the major categories of drugs affecting bacteria?
What are the major categories of drugs affecting bacteria?
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Which drug is NOT an example of a protein synthesis inhibitor?
Which drug is NOT an example of a protein synthesis inhibitor?
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What is the term used for the lowest concentration of a drug that inhibits microbial growth?
What is the term used for the lowest concentration of a drug that inhibits microbial growth?
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Narrow spectrum antibiotics affect a wide range of bacteria.
Narrow spectrum antibiotics affect a wide range of bacteria.
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What are Beta-lactamases?
What are Beta-lactamases?
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Which of the following drugs is an antimalarial?
Which of the following drugs is an antimalarial?
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What is one way to limit drug resistance in bacteria?
What is one way to limit drug resistance in bacteria?
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Which method is NOT used for antimicrobial susceptibility testing?
Which method is NOT used for antimicrobial susceptibility testing?
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What is a characteristic of semisynthetic drugs?
What is a characteristic of semisynthetic drugs?
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_____ drugs block metabolic pathways in bacteria.
_____ drugs block metabolic pathways in bacteria.
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Study Notes
Antimicrobial Chemotherapy
- Goal: Administer a drug to destroy an infective agent without harming the host's cells.
- Antimicrobial drugs can be produced naturally or synthetically.
- The "perfect drug" doesn't exist, but by balancing drug characteristics, a satisfactory compromise can usually be achieved.
Ideal Antimicrobial Drug Characteristics
- Selectively toxic: Harms the microbe but doesn't harm the host cells.
- Microbial: Kills the microbe rather than just inhibiting its growth.
- Long-lasting: Remains potent long enough to act and isn't broken down or excreted prematurely.
- Resistant: Not susceptible to the development of antimicrobial resistance.
- Complementary: Assists the host's defenses.
- Active in body fluids: Remains active even when diluted in body fluids and tissues.
- Easy delivery: Readily delivered to the site of infection.
- Affordable: Reasonably priced.
- Safe: Doesn't disrupt the host's health by causing allergies or predisposing the host to other infections.
Origins of Antimicrobial Drugs
- Antibiotics: Common metabolic products of aerobic bacteria and fungi.
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Sources:
- Bacteria: Genera Streptomyces and Bacillus
- Molds: Genera Penicillium and Cephalosporium
- Antibiotic producers compete less for nutrients and space by inhibiting other microbes in their habitat.
Terminology
- Chemotherapeutic drug: Any chemical used in the treatment, relief, or prevention of a disease.
- Prophylaxis: Use of a drug to prevent potential infection in a person at risk.
- Antimicrobial chemotherapy: The use of chemotherapeutic drugs to control infection.
- Antimicrobials: All-inclusive term for any antimicrobial drug, regardless of origin.
- Antibiotics: Substances produced naturally by microorganisms that can inhibit or destroy other microorganisms.
- Semisynthetic drugs: Drugs that are chemically modified in the laboratory after being isolated from natural sources.
- Synthetic drugs: Antimicrobial compounds synthesized entirely in the laboratory.
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Spectrum: The range of microbial types a drug is effective against.
- Narrow-spectrum: Effective on a small range of microbes.
- Broad-spectrum: Effective against a wide variety of microbial types.
Drug Spectrum
- Narrow-spectrum drugs: Target specific cell components found only in certain microbes, like Bacitracin.
- Broad-spectrum drugs: Target cell components common to most pathogens.
Antibiotics
- Antibiotics are produced by bacteria and fungi.
- Antibiotics inhibit or kill other microbes without harming the host.
Chemotherapeutic Drugs
- Chemotherapeutic drugs treat disease by targeting specific metabolic pathways in microorganisms.
- Prophylaxis: Using drugs to prevent the development of infection in susceptible individuals.
- Antimicrobial chemotherapy: Use of drugs to control infection.
- Selective toxicity: Antimicrobial drugs must harm microbial cells without damaging host cells.
Drug Categories
- Beta-lactamases: are enzymes produced by bacteria to circumvent the antibiotic's effects.
- Metabolic analogs function like normal metabolites but block the microbe's metabolic pathway.
Antibiotics
- Semisynthetic drugs: are chemically modified natural antibiotics to improve properties.
- Synthetic drugs: are completely manufactured.
Spectrum of Activity
- Narrow-spectrum drugs: Target a limited range of microorganisms.
- Broad-spectrum drugs: Effective against a wider range of microbes.
- Synergistic effects: Occur when two drugs work together to enhance their effectiveness.
Drug Targets on Bacterial Cells
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Cell wall synthesis inhibitors: Block the formation of peptidoglycan, a major component of bacterial cell walls.
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Beta-lactams:
- Penicillin: Inhibits transpeptidases (enzymes that cross-link peptidoglycan).
- Cephalosporins: More resistant to beta-lactamases and have a broader spectrum of activity.
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Non-Beta-lactam cell wall inhibitors:
- Bacitracin: Blocks the transport of peptidoglycan precursors across the cytoplasmic membrane.
- Isoniazid: Targets synthesis of mycolic acid, a unique component of the cell wall of Mycobacterium tuberculosis.
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Beta-lactams:
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Damage to cell membranes:
- Interact with phospholipids in the cytoplasmic membrane, disrupting membrane integrity.
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DNA/RNA inhibitors
- Fluoroquinolones: Interfere with DNA gyrase, a bacterial enzyme that unwinds DNA during replication.
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Protein synthesis inhibitors
- Aminoglycosides: Bind to the 30S ribosomal subunit, interfering with mRNA translation.
- Tetracyclines: Block the attachment of tRNA to the ribosome, inhibiting protein synthesis.
- Chloramphenicol: Prevents peptide bond formation.
- Macrolides: Bind to the 50S ribosomal subunit, preventing the translocation of tRNA.
- Oxazolidinones: Inhibit initiation of protein synthesis.
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Blocking metabolic pathways
- Sulfa drugs: Act as competitive inhibitors of enzymes, blocking synthesis of folic acid, essential for bacterial growth.
Antimalarial Drugs
- Quinine and Chloroquine are effective against malaria parasites.
Antifungal Drugs
- Synthetic azoles and flucytosine target fungal cell wall synthesis and nucleic acid synthesis.
Antiviral Chemotherapy
- Targets specific viral structures or proteins involved in replication.
Drug Resistance
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Transfer of drug resistance: Occurs through:
- R factors (plasmids): Carry genes that encode resistance mechanisms.
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Mechanisms of acquired bacterial drug resistance:
- Inactivation of the drug: Enzymes modify or break down the antibiotic.
- Decreased permeability of drug: Alteration of bacterial cell membrane reduces drug entry.
- Alteration of the drug target: Mutations in the target site prevent drug binding.
- Enzymatic bypass: Microbes develop alternative pathways for essential processes, circumventing the action of drugs.
Limiting Drug Resistance
- Use antibiotics only when necessary: Reduce selective pressure for resistant strains.
- Administer antibiotics at appropriate doses and for the full duration: Prevents development of resistance.
- Develop new drugs: Overcome existing resistance mechanisms.
- Develop new drugs: Overcome existing resistance mechanisms
Minimum Inhibitory Concentration (MIC)
- MIC: The lowest concentration of a drug that inhibits microbial growth.
Antimicrobial Susceptibility Testing
- Kirby-Bauer: Disk diffusion procedure assesses the sensitivity of a microbe to various antibiotics.
- E-test: Provides a quantitative measurement of the MIC.
- Tube dilution method: Determines the MIC by testing serial dilutions of the antibiotic.
Therapeutic Index
- Therapeutic index: A measure of the drug's safety. A high therapeutic index indicates a drug is more effective at therapeutic levels than harmful at toxic levels.
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Description
Discover the principles of antimicrobial chemotherapy, focusing on the essential characteristics of ideal antimicrobial drugs. Learn about how these drugs target infections while sparing the host's cells and the importance of balancing drug properties for effective treatment.