Chapter 5: Antibiotics that Target the Cell Envelope
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Questions and Answers

Why is it difficult for β-lactam antibiotics to reach their targets in gram-negative bacteria?

  • The porins are protein channels that block β-lactam antibiotics
  • The PBPs are hidden behind the porins
  • The outer membrane is impermeable to β-lactam antibiotics (correct)
  • The peptidoglycan layer is too thick

    • What is the functional group attached to the 1st carbon atom in the beta-lactam ring of penicillins?

  • CH3
  • O
  • NH
  • COOH (correct)

    • What is the role of porins in facilitating the action of β-lactam antibiotics?

  • They enhance the activity of β-lactam antibiotics
  • They provide a channel for β-lactam antibiotics to diffuse through the outer membrane (correct)
  • They break down the peptidoglycan layer
  • They inhibit the activity of PBPs

    • Which of the following is a characteristic of natural penicillins?

    <p>They are the oldest members of the penicillin antibiotic family</p> Signup and view all the answers

    What is the primary reason why a β-lactam antibiotic cannot kill a bacterium?

    <p>The antibiotic cannot get to the bacterium</p> Signup and view all the answers

    What type of bacteria have relatively exposed PBPs and peptidoglycan layers?

    <p>Gram-positive bacteria</p> Signup and view all the answers

    What is the R group in the structure of penicillins?

    <p>A variable side chain</p> Signup and view all the answers

    What is the name of the protein channels in the outer membrane that β-lactam antibiotics must diffuse through?

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

    Which of the following is NOT a type of penicillin?

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

    What is the consequence of a β-lactam antibiotic being unable to reach its target in a bacterium?

    <p>The antibiotic is unable to kill the bacterium</p> Signup and view all the answers

    What is the combination of ampicillin with sulbactam used for?

    <p>To inhibit β-lactamase</p> Signup and view all the answers

    Which of the following penicillins is an oral agent?

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

    What is the function of β-lactamase inhibitors in penicillins?

    <p>To inhibit the degradation of penicillins by β-lactamase</p> Signup and view all the answers

    What is the term for the combination of a penicillin with a β-lactamase inhibitor?

    <p>Protected penicillin</p> Signup and view all the answers

    What is the primary limitation of antistaphylococcal penicillins in terms of their spectrum of activity?

    <p>Their inability to bind to the PBPs of MRSA and MRSE bacteria</p> Signup and view all the answers

    Which of the following bacteria is not typically treated with antistaphylococcal penicillins?

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

    What is the main reason why antistaphylococcal penicillins are not used to treat enterococcal infections?

    <p>They are less effective against enterococci due to the bulkiness of their side chains</p> Signup and view all the answers

    Which of the following is a characteristic of antistaphylococcal penicillins that limits their spectrum of activity?

    <p>The bulkiness of their side chains</p> Signup and view all the answers

    What is the primary use of antistaphylococcal penicillins?

    <p>Treating staphylococcal infections</p> Signup and view all the answers

    Which of the following antibiotics is no longer commercially available?

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

    What is the term for the group of antibiotics that includes nafcillin, oxacillin, and dicloxacillin?

    <p>Antistaphylococcal penicillins</p> Signup and view all the answers

    Why are antistaphylococcal penicillins less effective against streptococci?

    <p>The bulkiness of the side chains limits their ability to penetrate streptococcal cells</p> Signup and view all the answers

    What is the reason for piperacillin's name?

    <p>The presence of a piperazine derivative in its side chain</p> Signup and view all the answers

    Compared to aminopenicillins, extended-spectrum penicillins are more resistant to cleavage by which type of enzymes?

    <p>Gram-negative β-lactamases</p> Signup and view all the answers

    What is the activity of extended-spectrum penicillins against gram-positive bacteria?

    <p>They have moderate activity against gram-positive bacteria</p> Signup and view all the answers

    What is the activity of piperacillin against Pseudomonas aeruginosa?

    <p>It has high activity against Pseudomonas aeruginosa</p> Signup and view all the answers

    Which of the following bacteria is susceptible to the β-lactamases of staphylococci?

    <p>Natural penicillins</p> Signup and view all the answers

    What is the activity of extended-spectrum penicillins against anaerobes?

    <p>They have modest activity against anaerobes</p> Signup and view all the answers

    What is the difference between piperacillin and ticarcillin?

    <p>Piperacillin has a broader spectrum of activity than ticarcillin</p> Signup and view all the answers

    Which of the following bacteria is not typically susceptible to extended-spectrum penicillins?

    <p>Staphylococcus aureus</p> Signup and view all the answers

    What is the primary action of penicillins in bacteria?

    <p>Inhibiting the assembly of bacterial cell walls</p> Signup and view all the answers

    Which type of bacteria are natural penicillins most active against?

    <p>Aerobic gram-positive bacteria and anaerobic bacteria</p> Signup and view all the answers

    What is the effect of adding a β-lactamase inhibitor to an aminopenicillin?

    <p>Expanding the spectrum of activity to include many aerobic gram-negative bacteria and additional anaerobes</p> Signup and view all the answers

    What is the characteristic of extended-spectrum penicillins compared to aminopenicillins?

    <p>Improved activity against aerobic gram-negative bacteria</p> Signup and view all the answers

    What is the effect of using extended-spectrum penicillins in combination with β-lactamase inhibitors?

    <p>Making them among the most powerful antibacterial agents available</p> Signup and view all the answers

    Which type of bacteria are antistaphylococcal penicillins useful in treating infections caused by?

    <p>Staphylococcus aureus</p> Signup and view all the answers

    What is the spectrum of activity of extended-spectrum penicillins when used in combination with β-lactamase inhibitors?

    <p>Most aerobic gram-positive bacteria, aerobic gram-negative bacteria, and anaerobic bacteria</p> Signup and view all the answers

    What is the characteristic of aminopenicillins compared to natural penicillins?

    <p>Improved activity against aerobic gram-negative bacteria</p> Signup and view all the answers

    What is required for the synthesis of new proteins in bacteria?

    <p>RNA, amino acids, and energy-containing nucleoside triphosphates</p> Signup and view all the answers

    What is the estimated energy required to add a single amino acid to a growing protein?

    <p>The energy of three or four nucleoside triphosphates</p> Signup and view all the answers

    What is the first step in the synthesis of new proteins in bacteria?

    <p>Acquisition of raw materials or building blocks</p> Signup and view all the answers

    What is the role of special bacterial enzymes in the synthesis of new proteins?

    <p>To transcribe template bacterial genes into RNA</p> Signup and view all the answers

    What is the result of the synthesis of new proteins in bacteria?

    <p>The replacement of old worn-out parts and building of new bacteria</p> Signup and view all the answers

    Why is protein production in bacteria amenable to inhibition by antibiotics?

    <p>Because some of the bacterial components essential for these processes differ significantly from their human cell counterparts</p> Signup and view all the answers

    What do bacteria acquire from the human body?

    <p>Resources to allow for replacement of old worn-out parts and for building new bacteria</p> Signup and view all the answers

    What is the purpose of invading the human body for bacteria?

    <p>To acquire resources to allow for replacement of old worn-out parts and for building new bacteria</p> Signup and view all the answers

    What is the term for the potential energy stored in the gradient between the interior and exterior of the cell?

    <p>Proton motive force</p> Signup and view all the answers

    What is the direction of proton flow down the gradient in bacterial cells?

    <p>From outside to inside the cell</p> Signup and view all the answers

    What is the result of protons flowing down the gradient through the cytoplasmic membrane?

    <p>Active transport of nutrients</p> Signup and view all the answers

    What is the energy source used to power the synthesis of RNA during transcription?

    <p>Nucleoside triphosphates</p> Signup and view all the answers

    What is the enzyme complex used by bacteria to synthesize RNA during transcription?

    <p>RNA polymerase</p> Signup and view all the answers

    What is the type of RNA synthesized during transcription in bacterial cells?

    <p>Messenger RNA</p> Signup and view all the answers

    What is the process by which the information in the DNA of a bacterial gene is used to synthesize an RNA molecule?

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

    What is the ultimate product of the process of protein production in bacterial cells?

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

    What is the role of THF in bacterial synthesis?

    <p>Synthesis of nucleotides</p> Signup and view all the answers

    Why is the THF synthetic pathway an attractive target for antimicrobial compounds?

    <p>Because most bacteria cannot absorb folate from their environment</p> Signup and view all the answers

    What is the consequence of twisting one end of the DNA while holding the other end fixed?

    <p>Increased number of nucleotide pairs per helical turn</p> Signup and view all the answers

    What is the role of topoisomerase enzymes in DNA replication?

    <p>To relax the DNA molecule</p> Signup and view all the answers

    What is the result of supercoiling in DNA?

    <p>Decreased stability of the DNA molecule</p> Signup and view all the answers

    What is the structure of DNA that dictates the number of nucleotide pairs per helical turn?

    <p>Double helix</p> Signup and view all the answers

    What is the function of DNA polymerase in bacterial chromosome replication?

    <p>To synthesize new DNA strands</p> Signup and view all the answers

    What is the relationship between the number of nucleotide pairs per helical turn and the relaxation of DNA?

    <p>Decreased number of nucleotide pairs per helical turn leads to relaxation of DNA</p> Signup and view all the answers

    Study Notes

    β-Lactam Antibiotics

    • β-Lactam antibiotics cannot kill bacteria if they cannot reach the bacteria
    • β-Lactam antibiotics must breach the outer membrane of gram-negative bacteria through porins

    Penicillins

    • Penicillins have a β-lactam ring and a thiazolidine ring
    • Variable side chains can be attached to the β-lactam ring
    • Examples of penicillins: penicillin G, penicillin V, nafcillin, oxacillin, dicloxacillin, ampicillin, amoxicillin

    Natural Penicillins

    • Natural penicillins are effective against aerobic gram-positive bacteria and anaerobic bacteria
    • Natural penicillins have poor activity against aerobic gram-negative bacteria and most atypical bacteria

    Antistaphylococcal Penicillins

    • Antistaphylococcal penicillins are effective against staphylococcal infections
    • Antistaphylococcal penicillins are less effective against streptococci and are not used to treat them
    • Antistaphylococcal penicillins are inactive against MRSA and MRSE bacteria

    Aminopenicillins

    • Aminopenicillins have improved activity against aerobic gram-negative bacteria
    • Examples of aminopenicillins: ampicillin, amoxicillin

    Extended-Spectrum Penicillins

    • Extended-spectrum penicillins are more resistant to cleavage by gram-negative β-lactamases
    • Extended-spectrum penicillins are more active against gram-negative bacteria, including P. aeruginosa
    • Examples of extended-spectrum penicillins: piperacillin, ticarcillin
    • Extended-spectrum penicillins have modest activity against anaerobes

    β-Lactamase Inhibitors

    • β-Lactamase inhibitors can be added to extended-spectrum penicillins to extend their activity
    • The addition of a β-lactamase inhibitor expands the spectrum of extended-spectrum penicillins to include most enteric gram-negative bacilli

    Protein Production in Bacteria

    • Protein production in bacteria involves transcription and translation, similar to human cells.
    • The process requires raw materials such as RNAs, amino acids, and energy-containing nucleoside triphosphates.

    Transcription

    • Transcription is the process by which bacterial gene DNA is used to synthesize messenger RNA (mRNA).
    • The enzyme RNA polymerase is used to accomplish transcription.
    • Tetrahydrofolate (THF) is required for the ultimate synthesis of several nucleotides.

    Tetrahydrofolate (THF) Synthesis

    • Bacteria must synthesize THF, as they are unable to absorb folate from their diet.
    • The synthetic pathway of THF is a target for antimicrobial compounds.

    DNA Replication

    • DNA polymerase is responsible for replicating the bacterial chromosome.
    • Topoisomerases regulate supercoiling, or twisting of the DNA, during replication.

    Supercoiling

    • Supercoiling occurs when the DNA double helix is twisted, increasing or decreasing the number of nucleotide pairs per helical turn.
    • This process is accommodated by the formation of supercoils.

    Energy Requirements

    • The synthesis of new proteins requires abundant amounts of building blocks and energy.
    • It is estimated that the energy of three or four nucleoside triphosphates (e.g., ATP or GTP) is required to add a single amino acid to a growing protein.

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    Description

    This quiz covers the antibiotics that target the cell envelope, including β-lactam antibiotics, penicillins, cephalosporins, carbapenems, and monobactams. It also discusses the limitations of these antibiotics.

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