Microbiology Chapter 20 Quiz
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Questions and Answers

The following are true of Penicillin with the exception of:

  • It kills bacteria.
  • It inhibits gram-positive cell wall synthesis.
  • It does not affect eukaryotic cells.
  • It has selective toxicity.
  • It inhibits protein synthesis of bacteria. (correct)

    • A drug that inhibits mitosis, such as griseofulvin, would be more effective against:

  • Gram-negative bacteria.
  • Fungi. (correct)
  • Gram-positive bacteria.
  • Wall-less bacteria.
  • Mycobacteria.

    • Most of the available antimicrobial agents are effective against:

  • Protozoa.
  • Fungi.
  • Bacteria. (correct)
  • All of the answers are correct.
  • Viruses.

    • In what way are semisynthetic penicillins and natural penicillins alike?

    <p>Both are based on β-lactam.</p> Signup and view all the answers

    Which of the following antibiotics is NOT bactericidal?

    <p>Polyenes.</p> Signup and view all the answers

    Which one of the following does NOT belong with the others?

    <p>Streptomycin.</p> Signup and view all the answers

    Which of the following antimicrobial agents has the fewest side effects?

    <p>Penicillin.</p> Signup and view all the answers

    Which of the following antimicrobial agents is recommended for use against fungal infections?

    <p>Amphotericin B.</p> Signup and view all the answers

    Who is the individual that first identified penicillin coming from the mold penicillium?

    <p>Fleming.</p> Signup and view all the answers

    Actinobacteria or actinomycetes is a phylum of Gram-positive bacteria with high _____ and _____ content in their DNA.

    <p>guanine, cytosine</p> Signup and view all the answers

    The classic example of a broad-spectrum antibiotic is:

    <p>Amoxicillin.</p> Signup and view all the answers

    The following are modes of action of antimicrobial drugs with the exception of:

    <p>Irreversible mitochondrial damage.</p> Signup and view all the answers

    _________ are applied to nonliving surfaces or substances with the intent of purifying an area of all or most microorganisms that could cause harm.

    <p>disinfectants</p> Signup and view all the answers

    Which of the following antibiotics does NOT interfere with cell wall synthesis?

    <p>Macrolides.</p> Signup and view all the answers

    Drug resistance occurs:

    <p>When antibiotics are used indiscriminately.</p> Signup and view all the answers

    The following results were obtained from a disk-diffusion test for microbial susceptibility to antibiotics. In Table 20.2, the most effective antibiotic tested was:

    <p>D.</p> Signup and view all the answers

    Which of the following would be selective against the tubercle bacillus?

    <p>Ethambutol - inhibits mycolic acid synthesis.</p> Signup and view all the answers

    In the presence of penicillin, a cell dies because:

    <p>It undergoes lysis.</p> Signup and view all the answers

    Mebendazole is used to treat cestode infections. It interferes with microtubule formation; therefore, it would NOT affect:

    <p>Bacteria.</p> Signup and view all the answers

    An example of a competitive inhibitor of the synthesis of essential metabolites includes:

    <p>Sulfonamides.</p> Signup and view all the answers

    Beta-lactam antibiotics include which of the following:

    <p>Penicillins.</p> Signup and view all the answers

    This is an important 'last line' medication against antibiotic-resistant S. Aureus:

    <p>Vancomycin.</p> Signup and view all the answers

    The following drug can cause irreversible aplastic anemia:

    <p>Chloramphenicol.</p> Signup and view all the answers

    Fungi and animal cell membranes have different sterols. Which sterol is found on fungal membranes?

    <p>Ergosterol.</p> Signup and view all the answers

    Treatment for helminthic infection includes:

    <p>Praziquantel.</p> Signup and view all the answers

    Penicillin was considered a 'miracle drug' for all of the following reasons EXCEPT:

    <p>It was the first antibiotic.</p> Signup and view all the answers

    Which of the following statements about drug resistance is false?

    <p>It is found only in gram-negative bacteria.</p> Signup and view all the answers

    Drug resistance occurs:

    <p>When antibiotics are used indiscriminately.</p> Signup and view all the answers

    In Table 20.2, the most effective antibiotic tested was:

    <p>D.</p> Signup and view all the answers

    In Table 20.2, the antibiotic that exhibited bactericidal action was:

    <p>Can't tell.</p> Signup and view all the answers

    In Table 20.2, which antibiotic would be most useful for treating a Salmonella infection?

    <p>Can't tell.</p> Signup and view all the answers

    Which of the following would be selective against the tubercle bacillus?

    <p>Ethambutol - inhibits mycolic acid synthesis.</p> Signup and view all the answers

    In the presence of penicillin, a cell dies because:

    <p>It undergoes lysis.</p> Signup and view all the answers

    Lamisil is an allylamine used to treat dermatomycoses. Lamisil's method of action is similar to that of:

    <p>Azole antibiotics.</p> Signup and view all the answers

    Niclosamide prevents ATP generation in mitochondria. You would expect this drug to be effective against:

    <p>Helminths.</p> Signup and view all the answers

    The data in Table 20.3 show that these bacteria:

    <p>Developed resistance to antibiotics.</p> Signup and view all the answers

    Which of the following statements about drugs that competitively inhibit DNA polymerase or RNA polymerase is false?

    <p>They are too dangerous to use.</p> Signup and view all the answers

    The substrate for transpeptidase used to synthesize peptidoglycan is shown in Figure 20.5. Which of the drugs shown would inhibit peptidoglycan synthesis?

    <p>d.</p> Signup and view all the answers

    The structures of the influenza drug Tamiflu and sialic acid, the substrate for the influenza virus's neuramidase, are shown in Figure 20.6. What is the method of action of Tamiflu?

    <p>Competitive inhibition.</p> Signup and view all the answers

    Which of the following does NOT affect eukaryotic cells?

    <p>Semisynthetic penicillins.</p> Signup and view all the answers

    Mebendazole is used to treat cestode infections. It interferes with microtubule formation; therefore, it would NOT affect:

    <p>Bacteria.</p> Signup and view all the answers

    Which of the following antibiotics causes misreading of mRNA?

    <p>Aminoglycosides - changes shape of 30S units.</p> Signup and view all the answers

    The antibiotic actinomycin D binds between adjacent G-C pairs, thus interfering with:

    <p>Transcription.</p> Signup and view all the answers

    Study Notes

    Antibiotics and Antimicrobial Agents

    • Penicillin: Inhibits gram-positive cell wall synthesis and has selective toxicity but does not inhibit protein synthesis.
    • Griseofulvin: Effective against fungi by inhibiting mitosis.
    • Antimicrobial Agents: Most are effective against bacteria rather than viruses, fungi, or protozoa.
    • Semisynthetic Penicillins: Both semisynthetic and natural penicillins are based on β-lactam structure.

    Antibiotic Classification

    • Bactericidal vs. Bacteriostatic: Not all antibiotics are bactericidal; for example, polyene antibiotics are not bactericidal.
    • Mode of Action: Includes inhibition of cell wall synthesis, protein synthesis, and disruption of plasma membranes.
    • Broad-Spectrum Antibiotic: Amoxicillin is a classic example known for its effectiveness against a variety of bacteria.

    Specific Antibiotics and Their Uses

    • Amphotericin B: Recommended for fungal infections.
    • Streptomycin: Causes misreading of mRNA and inhibits protein synthesis.
    • Ethambutol: Selective against the tubercle bacillus by inhibiting mycolic acid synthesis.
    • Chloramphenicol: Binds to the 50S subunit of ribosomes, preventing peptide bond formation.

    Mechanisms of Drug Resistance

    • Drug Resistance: Occurs due to indiscriminate use of antibiotics and the transfer of resistant genes between bacteria. It is not limited to gram-negative bacteria.
    • Competitive Inhibition: Several drugs act as competitive inhibitors on biochemical pathways, including sulfonamides.

    Impacts of Antibiotic Use

    • Use in Animal Feed: Leads to antibiotic-resistant bacteria due to selective pressure where resistant strains survive and reproduce.
    • Selective Toxicity: Indicates that antibiotics are generally less harmful to eukaryotic cells compared to prokaryotic cells.

    Unique Properties and Actions

    • Actinobacteria: A phylum of gram-positive bacteria known for high guanine and cytosine content in DNA.
    • Fungal Membranes: Contain ergosterol, which is different from cholesterol found in animal cell membranes.

    Clinical Considerations

    • Minimal Inhibitory Concentration (MIC): The lowest concentration of an antibiotic that inhibits growth of a microorganism.
    • Minimal Bactericidal Concentration (MBC): The lowest concentration that kills the microorganism.
    • Adjunct Therapy: Using two antibiotics together can prevent drug resistance and reduce toxicity, but it does not guarantee increased effectiveness.

    Notable Figures in Antibiotic Discovery

    • Alexander Fleming: First identified penicillin from the mold Penicillium.

    Fungal and Helminthic Treatment

    • Mebendazole: Used for helminthic infections by interfering with microtubule formation, ineffective against bacteria.
    • Flucytosine: An antifungal agent effective against candidiasis.

    Mechanisms of Inhibition

    • Translation Inhibition: Different antibiotics affect peptide bond formation and ribosome function at various subunits (30S or 50S).
    • DNA/RNA Interference: Certain antibiotics inhibit nucleic acid synthesis and transcription processes.

    Side Effects and Risks

    • Chloramphenicol: Risk of causing aplastic anemia as a serious side effect.
    • Antimicrobial Peptides: Disrupt the plasma membrane as part of their antimicrobial action.

    Summary

    • Antibiotics vary widely in structure, function, and spectrum of activity, and understanding their mechanisms is crucial for effective treatment and combating antibiotic resistance.

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    Description

    Test your knowledge on key concepts from Microbiology Chapter 20 with these flashcard-style questions. This quiz covers important details about antibiotics such as Penicillin and the effects of various drugs on microorganisms. Challenge yourself and reinforce your understanding of microbiological treatments.

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