Antimicrobial Agents Overview
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Questions and Answers

What is the primary function of antimicrobial agents?

  • To promote the growth of microorganisms
  • To increase the resistance of the body to infections
  • To kill or inhibit the growth of microorganisms (correct)
  • To break down the cell walls of human cells

    • Antimicrobial agents can only be derived from synthetic sources.

    False (B)

    What is the primary target of action for penicillin-like antibiotics?

    Inhibition of cell wall synthesis

    The enzymes that penicillin binds to and inhibits are known as ______________.

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

    Match the following antimicrobial agents with their primary source:

    <p>Penicillin = Penicillium fungi Streptomycin = Streptomyces bacteria Griseofulvin = Penicillium fungi Erythromycin = Streptomyces bacteria Amphotericin B = Streptomyces bacteria</p> Signup and view all the answers

    Which of the following mechanisms is used by β-lactams to inhibit bacterial cell wall synthesis?

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

    Vancomycin can effectively treat infections caused by Gram-negative bacteria.

    <p>False (B)</p> Signup and view all the answers

    What is the primary mechanism by which polymyxins exert their antimicrobial effect?

    <p>Polymyxins disrupt both the cell membrane and outer membrane of bacteria by binding to phospholipids.</p> Signup and view all the answers

    Bacitracin inhibits bacterial cell wall synthesis by blocking the _____ of peptidoglycan subunits across the cell membrane.

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

    Match the following antimicrobial drugs with their primary mechanism of action:

    <p>Penicillins = Inhibition of peptidoglycan synthesis Polymyxins = Disruption of cell membrane Sulfonamides = Inhibition of folate synthesis Vancomycin = Inhibition of peptidoglycan synthesis</p> Signup and view all the answers

    Sulfonamides exhibit selective toxicity because they target a metabolic pathway essential for bacterial survival but not for human cells.

    <p>True (A)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of bacteriostatic antibiotics?

    <p>They cause cell death (A)</p> Signup and view all the answers

    How do sulfonamides and trimethoprim contribute to antimicrobial resistance?

    <p>Antimicrobial resistance can arise from mutations in bacterial enzymes involved in folate synthesis, allowing bacteria to bypass the inhibitory effects of sulfonamides and trimethoprim.</p> Signup and view all the answers

    Antimicrobial resistance is a global health concern that requires effective strategies to combat it.

    <p>True (A)</p> Signup and view all the answers

    Which of the following is NOT a method of resistance gene transfer?

    <p>Translation (D)</p> Signup and view all the answers

    Mobile genetic elements, such as plasmids and transposons, can transfer genes between bacterial cells.

    <p>True (A)</p> Signup and view all the answers

    What is the main purpose of antibiotic susceptibility testing?

    <p>To determine whether a specific antibiotic will be effective in treating a bacterial infection.</p> Signup and view all the answers

    The ______ test is a common method for determining antibiotic susceptibility.

    <p>Kirby-Bauer</p> Signup and view all the answers

    Which of these factors can contribute to antibiotic resistance?

    <p>All of the above (D)</p> Signup and view all the answers

    Match the following methods of resistance gene transfer with their descriptions:

    <p>Conjugation = Direct transfer of genetic material between bacteria through cell-to-cell contact Transformation = Uptake of free DNA fragments from the environment by bacteria Transduction = Transfer of genetic material between bacteria mediated by bacteriophages</p> Signup and view all the answers

    What is the mechanism by which Amphotericin B works against fungal cells?

    <p>Disruption of plasma membranes by binding to sterols.</p> Signup and view all the answers

    Amphotericin B would be effective against bacterial cells.

    <p>False (B)</p> Signup and view all the answers

    Which of the following antibiotics is classified as a bactericidal agent?

    <p>Penicillin (A)</p> Signup and view all the answers

    The antibiotic Isoniazid is primarily effective against Gram-negative bacteria.

    <p>False (B)</p> Signup and view all the answers

    What are the two main categories of antibiotic classification based on their spectrum of activity?

    <p>Broad spectrum and narrow spectrum</p> Signup and view all the answers

    The antibiotic classification based on their chemical structure involves grouping antibiotics with similar __________.

    <p>molecular structures</p> Signup and view all the answers

    Match the following antibiotics with their respective chemical classes:

    <p>Penicillin = β-Lactams Gentamicin = Aminoglycosides Erythromycin = Macrolide antibiotics Sulphamethoxazole = Sulphonamides Ciprofloxacin = Quinolones</p> Signup and view all the answers

    A broad-spectrum antimicrobial drug targets:

    <p>A wide variety of bacteria, including both gram-positive and gram-negative species (C)</p> Signup and view all the answers

    The amount of medication given during a certain time interval is called the ______.

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

    Synergistic drug interactions enhance the efficacy of each drug when used together.

    <p>True (A)</p> Signup and view all the answers

    What is the primary goal when determining the optimal dosage of a drug?

    <p>To minimize the risk of side effects while achieving clinical cure.</p> Signup and view all the answers

    Match the following drug interactions with their characteristics:

    <p>Synergistic interaction = Drugs work together to enhance each other's effects Antagonistic interaction = Drugs interfere with each other's activity, leading to reduced therapeutic levels or increased toxicity</p> Signup and view all the answers

    Which of the following factors are considered when determining the dosage of a drug? (Select all that apply)

    <p>Severity of infection (A), Body mass (B), Age (C), Metabolism (D), Elimination (E), Route of administration (F)</p> Signup and view all the answers

    Give an example of an antagonistic drug interaction.

    <p>The use of antacids can interfere with the absorption of some antibacterials that require an acidic stomach environment for optimal absorption.</p> Signup and view all the answers

    Trimethoprim and sulfamethoxazole (Bactrim) are an example of a ______ interaction.

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

    Which of the following is NOT considered an ideal property of antimicrobial agents?

    <p>Susceptibility to developing resistance (D)</p> Signup and view all the answers

    Bacteriostatic antimicrobial agents cause irreversible inhibition of bacterial growth, which is not resumed even after drug elimination.

    <p>False (B)</p> Signup and view all the answers

    What is the term used to describe the ratio of effective dose to toxic dose of a drug, often considered an important factor in determining its safety and efficacy?

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

    The ability of an antimicrobial agent to reach the target location in the body at an effective concentration is crucial for its ______.

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

    Match the following antimicrobial agents with their typical anatomical distribution:

    <p>Ampicillin = Serum, CSF, Urine Vancomycin = Serum, CSF, Urine Ciprofloxacin = Serum, CSF, Urine Gentamicin = Serum, Urine Clindamycin = Serum Nitrofurantoin = Urine</p> Signup and view all the answers

    Which of the following is a characteristic of a bactericidal antimicrobial agent?

    <p>Kills targeted bacteria (B)</p> Signup and view all the answers

    A broad-spectrum antimicrobial agent is effective against a wide range of bacterial species.

    <p>True (A)</p> Signup and view all the answers

    What is the main advantage of using a narrow-spectrum antimicrobial agent over a broad-spectrum agent?

    <p>Reduced risk of developing resistance</p> Signup and view all the answers

    Flashcards

    β-lactams

    A class of antibiotics that includes penicillins, cephalosporins, monobactams, and carbapenems, inhibiting cell wall synthesis.

    Glycopeptides

    Antibiotics, such as vancomycin, that inhibit cell wall formation but are ineffective against Gram-negative bacteria due to size.

    Bacitracin

    An antibiotic that blocks the export of peptidoglycan subunits across the cell membrane, inhibiting cell wall synthesis.

    Polymyxins

    Antibacterial agents that bind to phospholipids in cell membranes, disrupting both inner and outer membranes.

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    Daptomycin

    A lipopeptide antibiotic that inserts into the plasma membrane, leading to cell death.

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    Bactericidal

    Antimicrobials that kill bacteria outright, causing cell death.

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    Bacteriostatic

    Antimicrobials that inhibit bacterial growth and metabolism rather than killing them directly.

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    Sulfonamides

    Antimicrobials that block folate synthesis enzymes, impairing DNA synthesis and metabolic processes in bacteria.

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    Selective toxicity

    Ability of antimicrobial agents to target pathogens without harming host cells.

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    Broad spectrum vs narrow spectrum

    Broad spectrum acts on a wide range of pathogens; narrow spectrum targets specific ones.

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    Bactericidal vs bacteriostatic

    Bactericidal kills bacteria; bacteriostatic inhibits bacterial growth.

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    Therapeutic index

    Ratio of the effective dose to the toxic dose of a drug.

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    Pharmacokinetics

    Study of how drugs are absorbed, distributed, metabolized, and excreted.

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    Risk of resistance

    Potential for bacteria to adapt and evade effects of antimicrobial agents.

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    Anatomic distribution

    Locations where specific antibacterial agents are effective in the body.

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    Importance of immune status

    The role of a patient’s immune system in choosing bactericidal or bacteriostatic drugs.

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    Conjugation

    Transfer of plasmids or transposons between bacteria through direct contact.

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    Transformation

    Uptake of DNA fragments from the environment by a bacterium.

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    Transduction

    Transfer of bacterial DNA from one bacterium to another via bacteriophages.

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    Antibiotic Susceptibility Testing

    Testing to determine if bacteria are resistant or susceptible to antibiotics.

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    Kirby-Bauer Test

    A laboratory method to test antibiotic resistance using paper disks with antibiotics.

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    Zone of Inhibition

    Area around an antibiotic disk where bacteria cannot grow, indicating susceptibility.

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    Factors of Antibiotic Resistance

    Environmental, drug-related, patient-related, and prescriber-related factors that contribute to resistance.

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    Antimicrobial agents

    Substances that kill or inhibit the growth of microorganisms.

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    Types of antimicrobial agents

    Includes antibacterial, antifungal, antiviral, and antiparasitic agents.

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    Cell wall synthesis inhibition

    A mechanism where agents bind to enzymes preventing cell wall formation, causing cell death.

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    Penicillin Binding Proteins

    Enzymes that are targeted by certain antibiotics to disrupt cell wall synthesis.

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    Osmotic shock

    Condition causing cell death when the cell wall integrity is compromised.

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    Narrow-spectrum antimicrobial

    Targets specific subsets of bacterial pathogens, e.g., Gram-positive bacteria only.

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    Broad-spectrum antimicrobial

    Targets a wide variety of bacterial pathogens, both Gram-positive and Gram-negative.

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    Dosage

    Amount of medication given over a specific time to achieve therapeutic levels without toxicity.

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    Route of Administration

    Pathway by which a drug is introduced into the body, e.g., oral, intravenous, or intramuscular.

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    Synergistic interaction

    Combination of two drugs leads to enhanced efficacy, better together than alone.

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    Antagonistic interaction

    One drug reduces effectiveness or increases potential toxicity of another.

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    Factors for determining dosage

    Considerations include body mass, metabolism, elimination, and patient condition.

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    Side effects of drugs

    Unwanted or negative reactions from medication, influenced by various factors.

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    Classification of antibiotics

    Antibiotics are classified based on chemical structure, mechanism of action, spectrum of activity, and mode of action.

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    Broad-spectrum antibiotics

    Antibiotics effective against a wide range of bacteria, including both Gram-positive and Gram-negative bacteria.

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    Narrow-spectrum antibiotics

    Antibiotics effective against specific types of bacteria, either Gram-positive or Gram-negative.

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    Study Notes

    Antimicrobial Therapy

    • Antimicrobial agents are agents that kill microorganisms or suppress their growth.
    • These are chemicals or medicines used to treat infections caused by microbes.
    • Antimicrobial agents include antibacterial medicines/antibiotics, antifungal agents, antiviral agents, and antiparisitic medicines.
    • Some antimicrobials are derived from natural sources, while others are synthetic.
    • Examples of naturally derived agents are actinomyces, streptomyces (which are microorganisms themselves) and fungi such as cephalosporium and penicillin (derived from fungi).
    • Antibiotics are antibacterial medicines used to treat bacterial infections.

    Mechanisms of Attacking Bacteria

    • Antimicrobial agents work in several ways to attack bacteria.
    • One mechanism of action is inhibition of cell wall synthesis. Penicillin, bacitracin, cephalosporin, and vancomycin are examples of these types of agents.
    • Another mechanism is the disruption of cell membrane function, with polymyxin as an example.
    • Inhibition of protein synthesis is another mechanism. Tetracycline, erythromycin, streptomycin, and chloramphenicol are examples of agents working by this mechanism.
    • Some antimicrobials work by inhibition of nucleic acid synthesis. Examples include rifamycins (inhibition of transcription), quinolones (inhibition of DNA replication).
    • Lastly action as antimetabolites. Examples: sulfonamides and trimethoprim.

    Modes of Action

    • Cell Wall Synthesis: Beta-lactams (penicillins, cephalosporins, carbapenems, monobactams), Vancomycin, and Bacitracin affect cell wall synthesis.
    • Folate Synthesis: Sulfonamides and Trimethoprim inhibit folate synthesis.
    • Nucleic Acid Synthesis: Quinolones and Rifampin affect DNA replication and RNA polymerase respectively.
    • Cell Membrane: Polymyxins disrupt cell membranes.
    • Protein Synthesis: Tetracyclines, Aminoglycosides, Macrolides, Chloramphenicol, and Streptogramins interfere with protein synthesis.

    Inhibitors of Cell Wall Synthesis

    • Beta-lactam antibiotics bind to penicillin-binding proteins (PBPs) which are enzymes crucial for cross-linking peptidoglycan in bacterial cell walls.
    • This binding prevents the formation of a functional cell wall, leading to bacterial cell death (osmotic shock).
    • Glycopeptides (e.g., vancomycin) also interfere with cell wall synthesis by binding to the peptidoglycan precursors, preventing their incorporation into the cell wall.
    • Bacitracin blocks the transport of peptidoglycan precursors across the membrane.

    Antimicrobial Agents that Disrupt Cell Membranes

    • Polymyxins bind to phospholipids in cell membranes, disrupting both the cell membrane and the outer membrane.
    • Lipopeptides (e.g., daptomycin) insert into the plasma membrane, leading to cell death.

    Sulfanilamide

    • Sulfanilamide’s mechanism of selective toxicity involves blocking folate synthesis in bacteria.
    • Human cells lack the enzyme needed for this process, making sulfanilamide toxic only to bacteria.

    Inhibition of Metabolism

    • Sulfonamides and Trimethoprim inhibit the action of enzymes in the folic acid synthesis pathway. This blockage prevents purine formation, thus blocking DNA synthesis.

    Antimicrobial Resistance

    • Intrinsic resistance: Bacteria's inherent resistance to an antibiotic, regardless of previous exposure.
    • Acquired resistance: Bacteria adapt or gain genes to become resistant via adaptation process or gene transfer.

    Antibiotic Targets

    • Resistance mechanisms to antibiotics can involve efflux, target modification, inactivation enzymes, and impermeabilization
    • Efflux pumps actively transport antimicrobial agents out of the cell.
    • Target modification involves altering the target site of the antibiotic to reduce its effectiveness.
    • Inactivating enzymes can break down and neutralize antimicrobial agents.
    • Impermeabilization makes the cell wall too thick for antibiotics.

    Mechanism of Antibiotic Resistance

    • Intrinsic resistance mechanisms, such as impermeability and efflux, are more predictable and inherent to certain bacteria species or environments.
    • Acquired resistance mechanisms are less predictable and involve modifications of the target site, inactivation of the antibiotic, reduced uptake, or increased efflux.
    • Target site modification can occur via chromosomal mutations, which change an antibiotic’s target location.
    • Horizontal gene transfer involves the transfer of resistance genes between bacteria, a common source of antibiotic resistance.
    • Biofilms are resistant to the effect of antibiotics, disinfectants, and chemicals as well as phagocytosis.
    • Efflux pumps actively export antibiotics.

    Enzymatic Inactivation

    • Bacteria produce enzymes (beta-lactamases) that hydrolyze the beta-lactam ring, rendering beta-lactam antibiotics ineffective.
    • Extended-spectrum beta-lactamases (ESBLs) are beta-lactamases that can break down a wider range of beta-lactams.
    • ESBLs are often plasmid-mediated, i.e., transferred between bacteria.
    • Other types of enzymatic inactivation include inactivation of antibiotics, or by altering their molecular target.

    Altering Target

    • Resistance to beta-lactam antibiotics, especially in S. aureus (MRSA) is due to the production of an alternative penicillin-binding protein (PBP2a).
    • M. tuberculosis (MDR-TB) may exhibit resistance due to rpoB gene mutations, which alter RNA polymerase, making it unresponsive to an antibiotic like rifampin.

    Biochemical Testing

    • Biochemical tests are used to identify bacteria based on their metabolic properties, such as the ability to ferment specific sugars and produce certain enzymes.

    Clinical Lab Standards

    • Clinical laboratories may use standardized methods for testing antimicrobial susceptibility or resistance, including disk diffusion methods or broth microdilution to determine effective concentrations.

    Factors Contributing to Antibiotic Resistance

    Environmental Factors: overcrowding, poor sanitation, increased travel, widespread use of antibiotics in agriculture. Drug-Related Factors: fake drugs, poor quality of drugs, excessive use of antibiotics, poor dispensing/handling, irrational fixed-dose combination of antimicrobials Patient-Related Factors: poor adherence to instructions, poverty, poor sanitation practices, lack of education, self-medication, and misconceptions. Prescriber-Related Factors: inappropriate drug use, excessive empiric poly-antimicrobial use, overuse of antimicrobials, and inadequate dosing.

    Ideal Properties of Antimicrobial Agents

    • Selective toxicity: affecting the pathogen without harming the host.
    • Spectrum of activity: narrow or broad, affecting a specific subset or a variety of bacteria, respectively.
    • Fast action: antibiotics should start working quickly.
    • Effective action (solid sites): antibiotics should fully penetrate the site of infection as well as tissues (like joint fluid or meninges).
    • Effective pharmakokinetics: drugs should be delivered to the site of infection at a successful rate.
    • Minimal risk of toxicity: drugs should have a low risk of harming the host.
    • Favorable therapeutic index: a high therapeutic index implies that the effective dose is much higher than the toxic dose.
    • Limited risk to resistance (the antibiotic must not encourage the growth of resistant bacteria)
    • Cost Effective
    • Stable during storage (no loss of potency & no degradation)

    Basic Features of Antimicrobial Agent Activity

    • Antibiotics should be appropriately distributed to target bacteria.
    • Drugs should attach to/enter/bind to the bacteria.

    Drug Interactions

    • Synergistic drug interactions: two or more antimicrobial drugs together may have a better effect, e.g., trimethoprim and sulfamethoxazole against bacterial growth.
    • Antagonistic drug interactions: two drugs may lessen the effect or the toxicity of the drugs when used together.

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