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chpt 20

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  • What is chemotherapy in microbiology?

    Chemotherapy is the use of drugs to treat a disease by interfering with the growth of microbes within a host.

  • Define antibiotic.

    An antibiotic is a substance produced by a microbe that, in small amounts, inhibits the growth of another microbe.

  • What is selective toxicity?

    Selective toxicity means killing harmful microbes without damaging the host.

  • Difference between broad-spectrum and narrow-spectrum antibiotics.

    Broad-spectrum antibiotics target both Gram-positive and Gram-negative bacteria, while narrow-spectrum target specific types of microbes.

  • What is a superinfection?

    A superinfection is the overgrowth of normal microbiota that is resistant to antibiotics, often causing resistant bacterial or fungal infections.

  • Five major modes of action of antimicrobial drugs.

    1. Inhibition of cell wall synthesis
    2. Inhibition of protein synthesis
    3. Inhibition of nucleic acid replication and transcription
    4. Injury to plasma membrane
    5. Inhibition of essential metabolic synthesis

  • Why are drugs targeting the bacterial cell wall bacteria-specific?

    Because bacterial cell walls contain peptidoglycan, which is absent in human cells, making these drugs selectively toxic to bacteria.

  • Examples of drugs that inhibit cell wall synthesis.

    Penicillins, cephalosporins, bacitracin, and vancomycin inhibit bacterial cell wall synthesis.

  • How do drugs inhibit protein synthesis in bacteria?

    They bind to bacterial ribosomal subunits (30S or 50S), blocking translation steps such as peptide formation or translocation.

  • Why is selective toxicity difficult for antiviral drugs?

    Viruses use host cell machinery and lack their own metabolism, making it hard to target viruses without harming host cells.

  • Two common tests to determine antimicrobial susceptibility.

    Disk diffusion (Kirby-Bauer) test and E-test (epsilometer) are used to assess antibiotic sensitivity and minimal inhibitory concentration (MIC).

  • What is MIC and MBC in antimicrobial testing?

    MIC is the minimal inhibitory concentration that stops growth; MBC is the minimal bactericidal concentration that kills bacteria.

  • Define drug resistance in microbes.

    Drug resistance is an adaptive response where microbes tolerate drug amounts that would normally inhibit them.

  • How do microbes acquire drug resistance?

    Through spontaneous mutations or horizontal gene transfer via plasmids (R factors) and transposons.

  • Examples of misuse of antibiotics that promote resistance.

    Using outdated drugs, treating viral infections, incomplete regimens, and using antibiotics in animal feed.

  • Difference between synergism and antagonism in drug combinations.

    Synergism: combined effect greater than individual effects.
    Antagonism: combined effect less than individual effects.

  • What are antimicrobial peptides and examples?

    Broad-spectrum agents like nisin (from lactic acid bacteria), defensins (human), magainin (frogs), and squalamine (sharks) used in new therapies.

  • What is the role of phage therapy in antimicrobial treatment?

    Phage therapy uses bacteriophages to target and kill specific bacterial pathogens as an alternative to antibiotics.

  • How do beta-lactam antibiotics work?

    They inhibit bacterial cell wall synthesis by binding to enzymes that cross-link peptidoglycan.

  • What is the significance of bacterial penicillinase?

    Penicillinase is an enzyme that breaks down penicillin, causing resistance to natural penicillins.