Commercial Modifications of Susceptibility Testing
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Questions and Answers

What was the cause of John McCrae's death?

  • Wounded in World War I
  • Blood infection
  • Streptococcal pneumonia/meningitis (correct)
  • Died in the Second Boer War

    • In which war did Norman Bethune serve and get wounded?

  • Spanish Civil War
  • World War I (correct)
  • Second Boer War
  • Second Sino-Japanese War

    • What led to the miraculous revolution in medicine and the curing of infectious diseases?

  • Treatment with a new experimental drug (correct)
  • Brought western medicine to China
  • Served in the Second Sino-Japanese War
  • Graduated from U of T in Medicine

    • Which enzyme is inhibited by trimethoprim in the folic acid biosynthesis pathway?

    <p>Enzyme #3</p> Signup and view all the answers

    What is the synergistic effect observed when trimethoprim and sulfonamide are used in combination?

    <p>Enhanced antimicrobial activity</p> Signup and view all the answers

    What is the substrate of the enzyme involved in folic acid biosynthesis that is structurally similar to sulfa drugs?

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

    What type of inhibition is exemplified by the action of sulfa drugs on the enzyme involved in folic acid biosynthesis?

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

    Which antibiotic irreversibly binds to the 30S ribosomal subunit, causing it to malfunction and blocking initiation of translation?

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

    Which antibiotic class is often the drug of choice for patients allergic to penicillin?

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

    Which antibiotic class interferes with protein synthesis at various steps?

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

    Which antibiotic is crucial for treating Gram-positive bacteria resistant to β-lactam drugs?

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

    Which antibiotic class has low affinity for Gram-positive bacteria?

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

    Which antibiotic class is effective against a wide range of bacteria and resists β-lactamases?

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

    Which antibiotic class has greater activity against Pseudomonas species?

    <p>Extended-spectrum penicillins</p> Signup and view all the answers

    Which antibiotic class is bacteriostatic and reversibly binds to the 30S subunit, blocking tRNA attachment?

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

    Which antibiotic inhibits topoisomerases and is bactericidal against a wide variety of bacteria?

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

    Which antibiotic blocks prokaryotic RNA polymerase from initiating transcription and is used to treat tuberculosis, Hansen’s disease, and meningitis?

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

    Which type of antimicrobial drug can be 'static' or 'cidal'?

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

    Who isolated Streptomycin from S. griseus?

    <p>Selman Waksman</p> Signup and view all the answers

    What test is commonly used to determine the susceptibility of bacterial strains to drugs?

    <p>The Kirby-Bauer disc diffusion test</p> Signup and view all the answers

    What is the main concern in the industry regarding antimicrobial drugs?

    <p>Few new antibiotics being developed</p> Signup and view all the answers

    'Antimicrobial drugs exhibit selective toxicity' - how is relative toxicity expressed?

    <p>$Therapeutic hinspace index$</p> Signup and view all the answers

    'Determining susceptibility of bacterial strains involves minimum inhibitory and bactericidal concentrations' - what does MIC stand for?

    <p>$Minimum hinspace inhibitory hinspace concentration$</p> Signup and view all the answers

    'Antimicrobials differ in behavior in the body, with some requiring multiple doses per day' - what term describes this behavior?

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

    Which antimicrobial drug was identified as most suitable for treating humans post-1960?

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

    What term describes combinations of antimicrobial drugs that can be antagonistic, synergistic, or additive?

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

    'Adverse effects of antimicrobial drugs include toxicity, allergic reactions, and suppression of normal microbiota' - what are normal microbiota also known as?

    <p>Normal flora</p> Signup and view all the answers

    'Antimicrobials differ in behavior in the body' - what term describes the study of the action of drugs within the body?

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

    'Antimicrobial drugs are classified as antibiotics, antifungals, antiparasitics, and antivirals' - what term describes their ability to affect only microbial cells while causing little or no harm to host cells?

    <p>Selective toxicity</p> Signup and view all the answers

    Who discovered the first successful antimicrobial chemical in 1910?

    <p>Paul Ehrlich</p> Signup and view all the answers

    Which discovery marked the finding of the first 'sulfa' drug?

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

    Who discovered the effectiveness of penicillin against bacterial species in 1928?

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

    Who led the efforts in 1941 to purify and test penicillin?

    <p>Howard Florey</p> Signup and view all the answers

    'Sulfa' drugs are derivatives of which antimicrobial chemical?

    <p>\text{Prontosil}</p> Signup and view all the answers

    'Ampicillin' and 'Methicillin' are chemical derivatives of which antimicrobial drug?

    <p>\text{Penicillin}</p> Signup and view all the answers

    Which method uses a strip with a gradient of drug to determine MIC?

    <p>E test</p> Signup and view all the answers

    What is the primary target of β-lactam drugs in bacteria?

    <p>Cell wall synthesis</p> Signup and view all the answers

    Which antibiotic interferes with the transport of peptidoglycan precursors across the cytoplasmic membrane?

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

    Which type of cells are weakened by penicillins, cephalosporins, and other β-lactam drugs?

    <p>Actively growing cells</p> Signup and view all the answers

    What is the mode of action of vancomycin in bacteria?

    <p>Inhibition of peptidoglycan synthesis</p> Signup and view all the answers

    Diffusion bioassay is used for comparing known concentrations with patient samples to yield drug concentration through:

    <p>Diffusion rates</p> Signup and view all the answers

    Study Notes

    Antimicrobial Drugs: Features and Susceptibility Testing

    • Penicillin, initially difficult to purify, was proven effective in humans by a police officer
    • Penicillin G identified as most suitable for treating humans post-1960
    • Streptomycin isolated by Selman Waksman from S. griseus, prompting further antibiotic screening
    • Few new antibiotics being developed, leading to a concern in the industry
    • Antimicrobial drugs exhibit selective toxicity, with relative toxicity expressed as therapeutic index
    • Antimicrobial drugs are classified as antibiotics, antifungals, antiparasitics, and antivirals
    • Antimicrobial drugs can be "static" (inhibit growth) or "cidal" (kill microbes), with varying spectra of activity
    • Combinations of antimicrobial drugs can be antagonistic, synergistic, or additive
    • Antimicrobials differ in behavior in the body, with some requiring multiple doses per day
    • Adverse effects of antimicrobial drugs include toxicity, allergic reactions, and suppression of normal microbiota
    • Determining susceptibility of bacterial strains involves minimum inhibitory and bactericidal concentrations
    • The Kirby-Bauer disc diffusion test is commonly used to determine the susceptibility of bacterial strains to drugs

    Commercial Modifications of Susceptibility Testing

    • Commercial modifications of susceptibility testing aim to be less labor-intensive and provide faster results.
    • One automated system uses turbidity in cards to determine growth rate and interprets results to determine minimum inhibitory concentrations (MICs) in 6–15 hours.
    • E test, a modification of the disc diffusion test, uses a strip with a gradient of drug to determine MIC. The intersection of the zone of inhibition indicates MIC.
    • Measuring concentration of antimicrobial drugs in blood or other body fluids is important to determine blood toxicity and achievable levels for new drugs.
    • Diffusion bioassay compares known concentrations with patient samples and produces a standard curve to yield drug concentration.
    • Drug targets of bacteria include cell wall synthesis, nucleic acid synthesis, cell membrane integrity, metabolic pathways, and protein synthesis.
    • β-lactam drugs competitively inhibit enzymes that help form peptide bridges between adjacent glycan chains in cell walls.
    • Vancomycin binds to the amino acid side chain of NAM molecules, blocking peptidoglycan synthesis.
    • Bacitracin interferes with the transport of peptidoglycan precursors across the cytoplasmic membrane.
    • Penicillins, cephalosporins, and other β-lactam drugs competitively inhibit enzymes that catalyze formation of peptide bridges between adjacent glycan strands, disrupting peptidoglycan synthesis.
    • These drugs weaken cell walls, leading to cell lysis and are only effective against actively growing cells.
    • Penicillins have a basic structure and side chain and are grouped into narrow-spectrum, penicillinase-resistant, and broad-spectrum categories based on their activity against Gram-positive and Gram-negative bacteria.

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    Description

    Learn about less labor-intensive, faster susceptibility testing methods such as automated systems and E test modifications for determining minimum inhibitory concentrations (MICs) in a shorter time frame. Understand the intersection of zone of inhibition to indicate MIC.

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