Bacterial Defense Mechanisms Quiz

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Questions and Answers

Which process involves the transfer of genetic material between bacteria through a bacteriophage?

  • Transduction (correct)
  • Transformation
  • Conjugation
  • Transcription

What is the role of efflux pumps in bacterial antibiotic resistance?

  • Inactivate the antibiotic (correct)
  • Facilitate bacterial DNA uptake
  • Modify the antibiotic structure
  • Alter the antibiotic's target site

What best describes the condition of bacterial persister cells?

  • They are actively replicating.
  • They have high metabolic rates.
  • They exist in a dormant state. (correct)
  • They are incapable of reverting to normal growth.

Which mechanism does bacteria use to become resistant by using existing, innate properties?

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

What is a significant characteristic of biofilms that contributes to antibiotic resistance?

<p>Sticky and slimy matrix formation. (C)</p> Signup and view all the answers

Which of the following methods of horizontal gene transfer involves the direct transfer of plasmids?

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

How can environmental changes affect antibiotic efficacy against bacteria?

<p>By creating conditions like altered pH and reduced oxygen. (D)</p> Signup and view all the answers

Which antibiotic class targets the bacterial cell wall?

<p>Beta-lactams (D)</p> Signup and view all the answers

What is the primary mechanism by which beta-lactams inhibit bacterial growth?

<p>Disrupt cell wall integrity (D)</p> Signup and view all the answers

Which of the following classes of beta-lactams is best known for treating drug-resistant organisms?

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

Which specific activity is NOT performed by Penicillin Binding Proteins (PBPs)?

<p>Catalyzing ATP synthesis (D)</p> Signup and view all the answers

Beta-lactams differ from each other based on which factor?

<p>Their side chains and ring structures (B)</p> Signup and view all the answers

What is a key feature of first-generation cephalosporins?

<p>Effective against Streptococcus and Staphylococcus (C)</p> Signup and view all the answers

Which of the following statements about PBPs is true?

<p>Different bacteria have different sets of PBPs (C)</p> Signup and view all the answers

What distinguishes aminopenicillins from regular penicillins?

<p>They have broader activity against gram-negative bacteria (D)</p> Signup and view all the answers

Why is it important that beta-lactams can evade certain resistance mechanisms?

<p>It enhances their therapeutic potency in resistant infections (D)</p> Signup and view all the answers

Which factors contribute to the diversity of beta-lactams?

<p>Variation in their affinity for PBPs (D)</p> Signup and view all the answers

What type of bacterial cell wall structure do beta-lactams primarily target?

<p>Peptidoglycan (C)</p> Signup and view all the answers

What is the primary characteristic of Extended-spectrum beta-lactamases (ESBLs)?

<p>Confer resistance principally to penicillins and cephalosporins (A)</p> Signup and view all the answers

Which of the following is NOT a characteristic of Carbapenemases?

<p>Usually chromosomally encoded (D)</p> Signup and view all the answers

What type of antibiotic does Vancomycin belong to?

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

Which of these antibiotics inhibit protein synthesis by inhibiting the formation of the peptide bond?

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

The most common ESBL gene associated with healthcare-associated infections is?

<p>blaCTX-M (C)</p> Signup and view all the answers

Which mechanism is characteristic of AmpC beta-lactamases?

<p>Induced production in presence of beta-lactam antibiotics (C)</p> Signup and view all the answers

Which of these antibiotic mechanisms is LEAST likely to lead to drug resistance?

<p>Decreased membrane permeability (B)</p> Signup and view all the answers

What consequence does binding of fluoroquinolones to topoisomerases have on microbial DNA?

<p>Inhibits replication fork progression and causes double-strand breaks (C)</p> Signup and view all the answers

What is the main mechanism of action of metronidazole?

<p>Production of toxic nitroso intermediates that cause DNA damage (A)</p> Signup and view all the answers

Which of the following antibiotics is considered effective against carbapenem-resistant infections?

<p>Cefiderocol (C)</p> Signup and view all the answers

What is the primary reason for using multiple antibiotics in treating infections with Enterococcus in endocarditis?

<p>To provide synergistic action by targeting different bacterial pathways (B)</p> Signup and view all the answers

Which of the following is NOT a valid reason for using multiple antibiotics in treating a community-acquired pneumonia?

<p>To increase the likelihood of eradicating the infection (A)</p> Signup and view all the answers

Which of the following is a mechanism of resistance in fluoroquinolones?

<p>Altered permeability barriers and efflux pumps (C)</p> Signup and view all the answers

Vancomycin-resistant Enterococcus (VRE) is characterized by the acquisition of which gene?

<p>vanA or vanB (A)</p> Signup and view all the answers

What is the intrinsic resistance of Vancomycin primarily attributed to?

<p>Size limitations preventing passage through Gram-negative membranes (D)</p> Signup and view all the answers

What is indicated by the mecA gene presence in Staphylococcus aureus?

<p>It indicates the presence of alternative PBP2a. (C)</p> Signup and view all the answers

Which resistance mechanism involves altering the affinity of penicillin-binding proteins (PBPs)?

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

Which of the following accurately describes beta-lactamase production?

<p>It hydrolyzes or inactivates beta-lactam antibiotics. (D)</p> Signup and view all the answers

Which of the following are examples of beta-lactamase enzymes?

<p>CTX-M and AmpC (B)</p> Signup and view all the answers

Which combination drug can counteract the effects of some beta-lactamases?

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

What is a function of efflux pumps in bacterial resistance mechanisms?

<p>To remove antibiotics from the bacterial cell. (A)</p> Signup and view all the answers

Which characteristic does NOT contribute to antibiotic resistance in bacteria?

<p>Increasing antibiotic permeability (C)</p> Signup and view all the answers

The absence of mecA in Staphylococcus aureus indicates what?

<p>The bacteria are likely sensitive to methicillin. (C)</p> Signup and view all the answers

Which of the following mechanisms can lead to decreased entry of antibiotics into bacterial cells?

<p>Decreased membrane permeability (B)</p> Signup and view all the answers

What type of resistance mechanism is involved when some bacteria produce enzymes to break down antibiotics?

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

Which antibiotic class specifically targets the synthesis of bacterial cell wall peptidoglycans?

<p>Beta-lactams (C)</p> Signup and view all the answers

Which of the following antibiotics specifically targets bacterial DNA gyrase, an essential enzyme involved in DNA replication?

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

Which antibiotic class primarily inhibits the synthesis of dihydrofolic acid, a crucial precursor for bacterial DNA synthesis?

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

Which antibiotic class, known for its effectiveness against anaerobic bacteria, disrupts DNA synthesis by interfering with the formation of DNA strands?

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

Which of the following antibiotic classes directly targets the bacterial ribosome, interfering with protein synthesis by inhibiting the formation of peptide bonds?

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

Which antibiotic class targets the production of a crucial precursor for bacterial DNA synthesis, dihydrofolic acid?

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

Which antibiotic class inhibits bacterial protein synthesis by interfering with the formation of peptide bonds?

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

Which antibiotic class targets bacterial DNA gyrase, an essential enzyme involved in DNA replication?

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

Flashcards

Intrinsic Resistance

Natural resistance of bacteria to antibiotics due to inherent traits.

Acquired Resistance

Resistance gained through genetic changes, often due to antibiotic exposure.

Efflux Pumps

Proteins that actively transport antibiotics out of bacterial cells.

Horizontal Gene Transfer

The movement of genetic material between organisms, leading to rapid spread of resistance.

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Transformation

The uptake of free DNA from the environment by bacteria.

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Conjugation

Transfer of genetic material between bacteria through direct contact.

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Biofilms

Aggregates of bacteria on surfaces protected by a sticky matrix, enhancing resistance.

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Persister Cells

Dormant bacterial cells that exhibit temporary tolerance to antibiotics.

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Cell Wall Inhibitors

Antibiotics that inhibit the synthesis of bacterial cell walls.

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Beta-lactams

A class of antibiotics that disrupt bacterial cell wall integrity by inhibiting transpeptidase.

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Transpeptidase

An enzyme involved in crosslinking peptidoglycan in bacterial cell walls.

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Penicillin Binding Proteins (PBPs)

Proteins that beta-lactams bind to, inhibiting their role in cell wall synthesis.

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Gram-positive vs Gram-negative

Two major types of bacteria distinguished by their cell wall structure and staining properties.

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Classes of Beta-lactams

Includes penicillins, cephalosporins, carbapenems, and monobactams, each with specific targets.

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Aminopenicillins

A subclass of penicillins effective against certain Gram-negative bacteria.

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Carbapenems

Broad-spectrum beta-lactams effective against multi-drug resistant bacteria.

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Cephalosporins

Beta-lactams often categorized into five generations, each with different bacterial targets.

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Broad-spectrum Antibiotics

Antibiotics effective against a wide variety of bacteria.

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Oxazolidinones

Class of antibiotics that block tRNAs from A site on the 30S ribosomal subunit.

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Polymyxins

Antibiotics that disrupt the outer membrane of Gram-negative bacteria.

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Rifampin

Antibiotic that inhibits RNA polymerase and is used in combination therapy.

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Sulfonamides

Antibiotics that block folate biosynthesis, crucial for DNA synthesis.

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Necrotizing Soft Tissue Infection

Severe infection requiring multiple antibiotics, including linezolid and piperacillin/tazobactam.

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Extended-spectrum beta-lactamases (ESBLs)

Enzymes that confer resistance to penicillins and cephalosporins.

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AmpC beta-lactamases

Enzymes providing resistance to penicillins and most cephalosporins, often chromosomally encoded.

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Carbapenemases

Enzymes that render carbapenems ineffective, indicating serious resistance.

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Vancomycin

A glycopeptide antibiotic that binds to D-ala D-ala, blocking cell wall synthesis.

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Vancomycin-resistant Enterococcus (VRE)

Bacteria that have acquired resistance to vancomycin via vanA or vanB genes.

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Fluoroquinolones

A class of antibiotics that target DNA gyrase and topoisomerase IV to prevent DNA replication.

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Ribosomal inhibitors

Antibiotics that affect protein synthesis by targeting bacterial ribosomes.

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PBP Mutations

Mutations in penicillin-binding proteins (PBPs) that reduce antibiotic binding affinity.

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mecA Gene

Gene that encodes an alternative PBP (PBP2a), responsible for MRSA resistance.

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MRSA vs MSSA

MRSA: mecA+ (methicillin-resistant), MSSA: mecA- (methicillin-sensitive).

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Beta-lactamases

Enzymes produced by bacteria that inactivate beta-lactam antibiotics.

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Common Beta-lactamases

Examples include CTX-M, AmpC, and Carbapenemases.

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Beta-lactamase inhibitors

Substances that protect beta-lactams from being inactivated by beta-lactamases.

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Combination Drugs

Drugs like Amoxicillin/clavulanate that pair beta-lactams with inhibitors.

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Decreased Membrane Permeability

A resistance mechanism where bacteria limit antibiotic entry through their cell membrane.

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Detecting Resistance

Methods include phenotypic assays (like PBP2a assay) and genotypic testing (mecA presence).

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Aminoglycosides

Antibiotics that target bacterial protein synthesis, primarily at the 30S ribosomal subunit.

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Nitroimidazole

A class of antibiotics that target DNA by disrupting its structure, effective against anaerobic bacteria.

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Study Notes

Bacterial Defense Mechanisms

  • Bacteria possess intrinsic and acquired resistance mechanisms.
  • Intrinsic resistance is a natural or innate property of the bacteria.
  • Acquired resistance emerges from exposure to antibiotics. This resistance is often under high selection pressure.

Resistance Mechanisms

  • Efflux Pumps: Pumps antibiotics out of the bacterial cell.
  • Permeability Barriers: Reduce antibiotic entry into the cell.
  • Target Bypass: The bacteria modifies the target of the antibiotic so it's ineffective.
  • Mutation: Changes in the bacterial DNA can reduce antibiotic effectiveness.
  • Horizontal Gene Transfer: Spread of resistance through transformation, conjugation, or transduction.

Biofilms

  • Bacteria clump together in biofilms on surfaces like rocks, roots, teeth, prosthetic devices, etc.
  • The sticky matrix composed of exopolysaccharides, proteins, DNA hinders antibiotic penetration.
  • Biofilms create an altered microenvironment with reduced oxygen and altered pH, impacting antibiotic effectiveness.
  • Persister cells become metabolically dormant, making antibiotics less successful.

Antibiotic Classes and Resistance

  • Cell Wall Inhibitors (Beta-lactams):

    • Disrupt cell wall integrity, preventing crosslinking.
    • Bind to penicillin-binding proteins (PBPs). Different bacteria/species of bacteria have different PBPs.
    • Resistance mechanisms include mutating PBPs, producing beta-lactamases (inactivating the antibiotic), and efflux pumps. Combinations of antibiotics (e.g., amoxicillin/clavulanate) address some resistance mechanisms.
    • Beta-lactamases (ESBLs, AmpC, Carbapenemases) are key resistance factors against beta-lactams. Several types, and treatment options vary according to the type of resistance experienced.

  • Cell Wall Inhibitors (Glycopeptides):

    • Targets the peptidoglycan, preventing cell-wall crosslinking.
    • Used against gram-positive bacteria, but ineffective against gram-negative bacteria due to size.
    • Resistance includes altering the dipeptide target molecule (e.g., in Vancomycin-resistant Enterococcus).

  • DNA Targeting Antibiotics (Fluoroquinolones):

    • Interfere with DNA replication by targeting topoisomerases (DNA gyrase and topoisomerase IV).
    • Resistance results from mutations in genes for these enzymes or the action of efflux pumps.

  • Ribosomal Inhibitors:

    • Macrolides, Lincosamides, Tetracyclines, and Aminoglycosides impact bacterial protein synthesis by targeting ribosomes.
    • Resistance involves modifying the ribosome, creating resistance enzymes, or using efflux.

  • Other Processes (Metronidazole, Rifampin, Sulfonamides, Polymyxins):

    • Target diverse bacterial processes beyond cell-wall synthesis or protein/RNA/DNA synthesis.
    • Mechanisms range from interfering with anaerobic environments to blocking folate biosynthesis or disrupting bacterial membranes.
    • Intrinsic resistance and acquired resistance exist in each class.

  • Aminoglycoside: Target site: Bacterial ribosome. Example: Gentamicin

  • Nitroimidazole: Target site: DNA. Example: Metronidazole

  • Rifampin: Target site: Bacterial RNA polymerase. Example: Rifampin

  • Sulfonamide: Target site: Folate synthesis. Example: Trimethoprim/sulfamethoxazole

  • Polymyxin: Target site: Bacterial cell membrane. Example: Colistin, Polymyxin B

Multiple Antibiotic Therapy

  • May be necessary for several reasons, including empiric coverage when the pathogen is unknown, polymicrobial infections, preventing antibiotic resistance, or treating highly burdened infections.

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