62 Questions
Why is it difficult for β-lactam antibiotics to reach their targets in gram-negative bacteria?
The outer membrane is impermeable to β-lactam antibiotics
What is the functional group attached to the 1st carbon atom in the beta-lactam ring of penicillins?
COOH
What is the role of porins in facilitating the action of β-lactam antibiotics?
They provide a channel for β-lactam antibiotics to diffuse through the outer membrane
Which of the following is a characteristic of natural penicillins?
They are the oldest members of the penicillin antibiotic family
What is the primary reason why a β-lactam antibiotic cannot kill a bacterium?
The antibiotic cannot get to the bacterium
What type of bacteria have relatively exposed PBPs and peptidoglycan layers?
Gram-positive bacteria
What is the R group in the structure of penicillins?
A variable side chain
What is the name of the protein channels in the outer membrane that β-lactam antibiotics must diffuse through?
Porins
Which of the following is NOT a type of penicillin?
Cephalosporins
What is the consequence of a β-lactam antibiotic being unable to reach its target in a bacterium?
The antibiotic is unable to kill the bacterium
What is the combination of ampicillin with sulbactam used for?
To inhibit β-lactamase
Which of the following penicillins is an oral agent?
Penicillin V
What is the function of β-lactamase inhibitors in penicillins?
To inhibit the degradation of penicillins by β-lactamase
What is the term for the combination of a penicillin with a β-lactamase inhibitor?
Protected penicillin
What is the primary limitation of antistaphylococcal penicillins in terms of their spectrum of activity?
Their inability to bind to the PBPs of MRSA and MRSE bacteria
Which of the following bacteria is not typically treated with antistaphylococcal penicillins?
Streptococci
What is the main reason why antistaphylococcal penicillins are not used to treat enterococcal infections?
They are less effective against enterococci due to the bulkiness of their side chains
Which of the following is a characteristic of antistaphylococcal penicillins that limits their spectrum of activity?
The bulkiness of their side chains
What is the primary use of antistaphylococcal penicillins?
Treating staphylococcal infections
Which of the following antibiotics is no longer commercially available?
Methicillin
What is the term for the group of antibiotics that includes nafcillin, oxacillin, and dicloxacillin?
Antistaphylococcal penicillins
Why are antistaphylococcal penicillins less effective against streptococci?
The bulkiness of the side chains limits their ability to penetrate streptococcal cells
What is the reason for piperacillin's name?
The presence of a piperazine derivative in its side chain
Compared to aminopenicillins, extended-spectrum penicillins are more resistant to cleavage by which type of enzymes?
Gram-negative β-lactamases
What is the activity of extended-spectrum penicillins against gram-positive bacteria?
They have moderate activity against gram-positive bacteria
What is the activity of piperacillin against Pseudomonas aeruginosa?
It has high activity against Pseudomonas aeruginosa
Which of the following bacteria is susceptible to the β-lactamases of staphylococci?
Natural penicillins
What is the activity of extended-spectrum penicillins against anaerobes?
They have modest activity against anaerobes
What is the difference between piperacillin and ticarcillin?
Piperacillin has a broader spectrum of activity than ticarcillin
Which of the following bacteria is not typically susceptible to extended-spectrum penicillins?
Staphylococcus aureus
What is the primary action of penicillins in bacteria?
Inhibiting the assembly of bacterial cell walls
Which type of bacteria are natural penicillins most active against?
Aerobic gram-positive bacteria and anaerobic bacteria
What is the effect of adding a β-lactamase inhibitor to an aminopenicillin?
Expanding the spectrum of activity to include many aerobic gram-negative bacteria and additional anaerobes
What is the characteristic of extended-spectrum penicillins compared to aminopenicillins?
Improved activity against aerobic gram-negative bacteria
What is the effect of using extended-spectrum penicillins in combination with β-lactamase inhibitors?
Making them among the most powerful antibacterial agents available
Which type of bacteria are antistaphylococcal penicillins useful in treating infections caused by?
Staphylococcus aureus
What is the spectrum of activity of extended-spectrum penicillins when used in combination with β-lactamase inhibitors?
Most aerobic gram-positive bacteria, aerobic gram-negative bacteria, and anaerobic bacteria
What is the characteristic of aminopenicillins compared to natural penicillins?
Improved activity against aerobic gram-negative bacteria
What is required for the synthesis of new proteins in bacteria?
RNA, amino acids, and energy-containing nucleoside triphosphates
What is the estimated energy required to add a single amino acid to a growing protein?
The energy of three or four nucleoside triphosphates
What is the first step in the synthesis of new proteins in bacteria?
Acquisition of raw materials or building blocks
What is the role of special bacterial enzymes in the synthesis of new proteins?
To transcribe template bacterial genes into RNA
What is the result of the synthesis of new proteins in bacteria?
The replacement of old worn-out parts and building of new bacteria
Why is protein production in bacteria amenable to inhibition by antibiotics?
Because some of the bacterial components essential for these processes differ significantly from their human cell counterparts
What do bacteria acquire from the human body?
Resources to allow for replacement of old worn-out parts and for building new bacteria
What is the purpose of invading the human body for bacteria?
To acquire resources to allow for replacement of old worn-out parts and for building new bacteria
What is the term for the potential energy stored in the gradient between the interior and exterior of the cell?
Proton motive force
What is the direction of proton flow down the gradient in bacterial cells?
From outside to inside the cell
What is the result of protons flowing down the gradient through the cytoplasmic membrane?
Active transport of nutrients
What is the energy source used to power the synthesis of RNA during transcription?
Nucleoside triphosphates
What is the enzyme complex used by bacteria to synthesize RNA during transcription?
RNA polymerase
What is the type of RNA synthesized during transcription in bacterial cells?
Messenger RNA
What is the process by which the information in the DNA of a bacterial gene is used to synthesize an RNA molecule?
Transcription
What is the ultimate product of the process of protein production in bacterial cells?
Protein
What is the role of THF in bacterial synthesis?
Synthesis of nucleotides
Why is the THF synthetic pathway an attractive target for antimicrobial compounds?
Because most bacteria cannot absorb folate from their environment
What is the consequence of twisting one end of the DNA while holding the other end fixed?
Increased number of nucleotide pairs per helical turn
What is the role of topoisomerase enzymes in DNA replication?
To relax the DNA molecule
What is the result of supercoiling in DNA?
Decreased stability of the DNA molecule
What is the structure of DNA that dictates the number of nucleotide pairs per helical turn?
Double helix
What is the function of DNA polymerase in bacterial chromosome replication?
To synthesize new DNA strands
What is the relationship between the number of nucleotide pairs per helical turn and the relaxation of DNA?
Decreased number of nucleotide pairs per helical turn leads to relaxation of DNA
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.
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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