Antimicrobial Chemotherapy

Questions and Answers

What is the mechanism of action of bacteriostatic agents?

Inhibition of cell wall synthesis

Inhibition of membrane function

Inhibition of protein synthesis or some bacterial metabolic pathways (correct)

Inhibition of nucleic acid synthesis

Which of the following antibiotics is classified as natural?

Synthetic antibiotic designed for greater effectiveness

Semisynthetic antibiotic

Aminoglycoside antibiotic

Naturally occurring antibiotic from fungal sources (correct)

What determines the therapeutic behavior of antibiotics with different skeletons?

Chemical structure (correct)

Spectrum of activity

Mode of action

Source of the antibiotic

Which of the following is NOT a classification of antibiotics based on function?

Antioxidants Signup and view all the answers

What is the key difference between Gram positive and Gram negative bacterial cell walls?

Thickness Signup and view all the answers

What is the primary goal of Paul Ehrlich's research in the early 1900s?

To synthesize chemical compounds that selectively kill infectious microbes Signup and view all the answers

What is the advantage of synthetic antibiotics over natural antibiotics?

All of the above Signup and view all the answers

What was the name of the compound discovered by Sahachiro Hata that targeted the bacterium Treponema pallidum?

Compound 606 Signup and view all the answers

Which of the following antibiotics is classified as a β-lactam?

Penicillin antibiotic Signup and view all the answers

What was Alexander Fleming's observation in 1928 that led to the discovery of penicillin?

That contaminating mould growth inhibited staphylococcal growth on one plate Signup and view all the answers

What is the primary target of antibiotics that inhibit bacterial cell wall synthesis?

Cell wall synthesis Signup and view all the answers

What is the term that refers to the use of chemicals or drugs to treat diseases?

Chemotherapy Signup and view all the answers

Which of the following is NOT a classification of antibiotics?

Classification based on color Signup and view all the answers

What is the mechanism of action of antimicrobial drugs?

They destroy or interfere with microbial structures and enzymes Signup and view all the answers

What is the name of the bacterium that causes syphilis?

Treponema pallidum Signup and view all the answers

Who is credited with the discovery of the first antimicrobial drug?

Sahachiro Hata Signup and view all the answers

What is the term that refers to the process by which microorganisms develop resistance to antibiotics?

Antimicrobial resistance Signup and view all the answers

What is the classification of antimicrobial agents based on their mechanism of action?

Drugs that inhibit cell wall synthesis, drugs that inhibit protein synthesis, and drugs that interfere with cell membrane integrity Signup and view all the answers

What is the mechanism of action of penicillins?

They mimic the D-alanyl-D-alanine residues and react covalently with the transpeptidase. Signup and view all the answers

What is the result of the combined action of a weakened cell wall, high internal osmotic pressure, and uncontrolled activity of autolytic enzymes in the cell wall?

The cell becomes deformed in shape and eventually bursts. Signup and view all the answers

What is the effect of adding an amino group (−NH2) to penicillin G?

It increases the spectrum of activity against gram-negative pathogens. Signup and view all the answers

What is the advantage of methicillin over other penicillins?

It is more resistant to enzymatic destruction by penicillinases. Signup and view all the answers

What is the characteristic of natural penicillins?

They are active against gram-positive bacteria and some gram-negative bacteria. Signup and view all the answers

What is the characteristic of aminopenicillins?

They have a wider range of activity and better oral absorption. Signup and view all the answers

What is the characteristic of extended-spectrum penicillins?

They are effective against pseudomonas bacteria. Signup and view all the answers

What is the effect of adding a hydroxyl group (−OH) to amoxicillin?

It increases the acid stability of amoxicillin. Signup and view all the answers

Why was methicillin developed?

To address the spread of enzymes (penicillinases) that were inactivating other penicillins. Signup and view all the answers

What is the primary reason for the increased resistance of cephalosporins to enzymatic inactivation by β-lactamases?

The fusion of the β-lactam ring to a six-member ring Signup and view all the answers

What is a key difference between cephalosporin C and penicillin in terms of their structural composition?

Cephalosporin C has two R groups, while penicillin has one R group Signup and view all the answers

What is the primary classification criterion for the generations of semisynthetic cephalosporins?

Their spectrum of activity Signup and view all the answers

What is a specific type of infection that cephalexin can be used to treat?

Bone infections Signup and view all the answers

What is a characteristic of third-generation cephalosporins?

Decreased activity against gram-positive organisms Signup and view all the answers

What is the main characteristic of first-generation cephalosporins?

They have excellent coverage against most gram-positive pathogens Signup and view all the answers

Which of the following is not a characteristic of fourth-generation cephalosporins?

No activity against gram-negative organisms Signup and view all the answers

What is an additional use of cephalosporin antibiotics?

Surgical prophylaxis Signup and view all the answers

What is the only monobactam used clinically?

Aztreonam Signup and view all the answers

What is a key difference between cephalosporins and penicillins in terms of their spectrum of activity?

Cephalosporins are more effective against gram-negative bacteria Signup and view all the answers

Which generation of cephalosporins includes cefoxitin?

Second generation Signup and view all the answers

What is the most recent development in the family of cephalosporins?

The development of fifth-generation cephalosporins Signup and view all the answers

What is a characteristic of second-generation cephalosporins?

Expanded gram-negative spectrum in addition to gram-positive spectrum Signup and view all the answers

Which of the following is a fifth-generation cephalosporin?

Ceftaroline Signup and view all the answers

What is the origin of cephalosporin C?

The fungus Cephalosporium acremonium Signup and view all the answers

What is a common feature of carbapenems and monobactams?

They have a β-lactam ring as part of their core structure Signup and view all the answers

Which of the following is not a characteristic of first-generation cephalosporins?

Expanded gram-negative spectrum Signup and view all the answers

Which generation of cephalosporins includes cefotaxime?

Third generation Signup and view all the answers

Which enzyme is responsible for attaching the NAG and NAM sugars to the growing peptidoglycan chain?

Peptidoglycan synthase Signup and view all the answers

What is the mechanism of action of Bacitracin in relation to bactoprenol?

It inhibits the dephosphorylation of bactoprenol Signup and view all the answers

Which stage of cell wall synthesis involves the cross-linking of peptide chains?

Stage 3: Cross-linking of polymers Signup and view all the answers

What is the role of transpeptidase in cell wall synthesis?

It cross-links the peptide chains of neighbouring peptidoglycan chains Signup and view all the answers

Which of the following β-lactam antibiotics inhibits the transpeptidase enzyme?

All of the above Signup and view all the answers

What is the result of the inhibition of transpeptidase by β-lactam antibiotics?

The inhibition of the cross-linking of peptide chains Signup and view all the answers

Which of the following is a function of phosphatase in relation to bactoprenol?

It recycles bactoprenol by removing the phosphate group Signup and view all the answers

What is the primary function of the cell wall in bacteria?

To provide shape and rigidity and protect against osmotic pressure changes Signup and view all the answers

Which of the following stages in cell wall synthesis is inhibited by Cycloserine and Fosfomycin?

Cytoplasmic stage Signup and view all the answers

What is the key difference between Gram positive and Gram negative bacterial cell walls in terms of peptidoglycan layers?

Gram positive bacteria have about 50-100 glycan layers Signup and view all the answers

What is the primary target of inhibitors of bacterial cell wall synthesis?

The formation of peptidoglycan layer Signup and view all the answers

What is the characteristic of bacteria that lack peptidoglycan?

They are resistant to inhibitors of bacterial cell wall synthesis Signup and view all the answers

What is the composition of peptidoglycan?

A combination of glycans and peptide cross links Signup and view all the answers

Which of the following is NOT a component of the Gram negative bacterial cell wall?

Teichoic acid Signup and view all the answers

What is the primary mechanism of action of vancomycin?

Binding to the end of the peptide chain of cell wall precursors Signup and view all the answers

What is the primary difference between β-lactam antibiotics and glycopeptides?

The mechanism of action on the bacterial cell wall Signup and view all the answers

What is the role of β-lactamase inhibitors in combination with β-lactam antibiotics?

To extend the antibiotic's spectrum of activity and increase stability against β-lactamases Signup and view all the answers

What is the primary function of the peptidoglycan precursors in bacterial cell wall synthesis?

To provide the building blocks for the bacterial cell wall Signup and view all the answers

What is the result of the inhibition of transpeptidase in bacterial cell wall synthesis?

Weak bacterial cell wall Signup and view all the answers

What is the primary mechanism of action of β-lactam antibiotics?

Inhibiting the transpeptidase enzyme Signup and view all the answers

What is the role of bactoprenol in bacterial cell wall synthesis?

To facilitate the transport of peptidoglycan precursors Signup and view all the answers

What is the primary function of the mRNA during protein synthesis?

To carry the codons that will be translated into amino acids Signup and view all the answers

Which of the following antibiotics acts by binding to the 30S subunit of bacterial ribosomes?

Aminoglycosides Signup and view all the answers

What is the result of the impairment of the proofreading ability of the ribosomal complex by aminoglycosides?

Production of proteins with incorrect amino acids Signup and view all the answers

What is the site of protein synthesis in the cell?

Cytoplasm Signup and view all the answers

What is the function of the ribosome during protein synthesis?

To translate the mRNA into protein Signup and view all the answers

What is the characteristic of aminoglycosides as antibiotics?

They are bactericidal Signup and view all the answers

What is the subunit of the ribosome that is targeted by aminoglycosides?

30S subunit Signup and view all the answers

What is the ultimate consequence of transpeptidase inhibition in bacterial cells?

Cell deformation and eventual lysis Signup and view all the answers

What is the mechanism of action of penicillins against bacterial cell walls?

Acting as alternative substrates for transpeptidases Signup and view all the answers

What is the primary advantage of aminopenicillins over natural penicillins?

Broader spectrum of activity against gram-negative bacteria Signup and view all the answers

What is the characteristic of methicillin that makes it resistant to enzymatic inactivation?

Modification of the R group to a bulkier dimethoxyphenyl group Signup and view all the answers

What is the result of the combined action of a weakened cell wall, high internal osmotic pressure, and uncontrolled activity of autolytic enzymes in the cell wall?

Cell deformation and eventual lysis Signup and view all the answers

What is the primary reason for the development of methicillin?

To address the spread of enzymes that inactivate natural penicillins Signup and view all the answers

What is the characteristic of extended-spectrum penicillins?

Broader spectrum of activity against gram-negative bacteria Signup and view all the answers

What is the primary target of antibiotics that inhibit bacterial cell wall synthesis?

Transpeptidase enzyme Signup and view all the answers

Which of the following β-lactam antibiotics is classified as a natural antibiotic?

Penicillin G Signup and view all the answers

What is the result of the inhibition of bactoprenol recycling in bacterial cell wall synthesis?

Accumulation of peptidoglycan precursors Signup and view all the answers

Which of the following antibiotics inhibits transpeptidase enzyme activity?

Penicillin G Signup and view all the answers

What is the role of peptidoglycan precursors in bacterial cell wall synthesis?

To provide the building blocks for cell wall synthesis Signup and view all the answers

Which of the following antibiotics targets the bacterial cell wall synthesis?

Penicillin G Signup and view all the answers

What is the mechanism of action of β-lactam antibiotics?

Inhibition of bacterial cell wall synthesis Signup and view all the answers

Which of the following is a consequence of the inhibition of bacterial cell wall synthesis?

Decreased bacterial growth Signup and view all the answers

What is the role of transpeptidase enzyme in bacterial cell wall synthesis?

To catalyze the formation of peptidoglycan Signup and view all the answers

Which of the following antibiotics is not a β-lactam antibiotic?

Sulfanilamide Signup and view all the answers

Study Notes

Brief Historical Perspective of Antimicrobial Chemotherapy

The term "chemotherapy" refers to the use of chemicals or drugs to treat diseases, not just cancer
Antimicrobial drugs target infectious microorganisms, destroying or interfering with their structures and enzymes to kill or inhibit their growth

Early Antimicrobial Drugs

Paul Ehrlich (1854-1915) discovered Compound 606, a "magic bullet" that targeted Treponema pallidum, the bacterium that causes syphilis
Alexander Fleming (1881-1955) discovered penicillin, which inhibits staphylococcal growth
Early antimicrobial drugs were natural products, often from fungal sources

Classification of Antimicrobial Agents

Classification based on source:
- Natural (naturally occurring, mostly from fungal sources)
- Semisynthetic (chemically altered natural products)
- Synthetic (designed to have greater effectiveness and less toxicity)
Classification based on spectrum of activity:
- Narrow spectrum
- Broad spectrum
Classification based on chemical structure:
- Different skeleton-containing antibiotics display different therapeutic behavior
- Similar structural units have similar patterns of toxicity and effectiveness
Classification based on function (mechanism of action):
- Cell wall synthesis inhibitors
- Inhibitors of membrane function
- Inhibitors of protein synthesis
- Inhibitors of metabolic pathways
- Inhibitors of nucleic acid synthesis

Drugs that Inhibit Bacterial Cell Wall Synthesis

Target Gram-positive and Gram-negative bacteria
Act by inhibiting transpeptidases, mimicking D-alanyl-D-alanine residues
Bacteria become deformed, eventually bursting due to weakened cell walls and high internal osmotic pressure

Penicillins

Natural penicillins: active against Gram-positive streptococci, staphylococci, and some Gram-negative bacteria
Penicillinase-resistant penicillins (e.g., methicillin, oxacillin, cloxacillin): active against beta-lactamase-producing bacteria
Aminopenicillins (e.g., ampicillin, amoxicillin): effective against a wider range of bacteria, with better oral absorption
Extended-spectrum penicillins (e.g., mezlocillin, piperacillin, ticarcillin): active against even more Gram-negative bacteria

Cephalosporins

β-Lactam ring fused to a six-member ring, providing resistance to enzymatic inactivation by β-lactamases
Originate from the fungus Cephalosporium acremonium
Have a similar spectrum of activity to penicillins against Gram-positive bacteria, but are active against more Gram-negative bacteria
Classified into generations based on spectrum of activity:
- First generation: narrow spectrum, active against Gram-positive bacteria
- Second generation: expanded Gram-negative spectrum
- Third generation: much expanded Gram-negative activity, but decreased activity against Gram-positive organisms
- Fourth generation: extended-spectrum agents, active against Gram-positive organisms, with greater resistance to beta-lactamases
- Fifth generation: ceftaroline, active against MRSA, with broad spectrum activity against Gram-negative bacteria

Other β-Lactam Antibiotics

Carbapenems: inhibit transpeptidase activity of penicillin-binding proteins
Monobactams: aztreonam, used clinically, inhibits bacterial cell wall synthesis

Bacterial Cell Wall

The bacterial cell wall provides shape and rigidity, and protects bacteria from changes in osmotic pressure.
Gram positive bacterial cell walls contain peptidoglycan and teichoic acid, and may or may not be surrounded by a protein or polysaccharide envelope.
Gram negative bacterial cell walls contain peptidoglycan, an extra lipid layer outside made up of lipopolysaccharide, lipoprotein, phospholipid, and protein.
The cell wall is confined in the periplasmic space between two lipid layers.

Peptidoglycan

Peptidoglycan, also known as murein, is a combination of glycans (sugars) and peptide cross links.
Glycans in peptidoglycan are N-acetyl glucosamine (NAG) and N-Acetyl Muramic acid (NAM).
Gram positive bacteria have about 50-100 glycan layers, while Gram negative bacteria have about 1-2 glycan layers.

Bacterial Cell Wall Synthesis

Cell wall synthesis proceeds in three stages: cytoplasmic stage, membrane stage (elongation and transfer), and extracellular stage (cross linking).
In the cytoplasmic stage, precursors (NAG and NAM) are synthesized. This stage is inhibited by Cycloserine and Fosfomycin.
In the membrane stage, precursors are transferred from the cytosol to the membrane and incorporated into the growing peptidoglycan. This stage is inhibited by Bacitracin and Vancomycin.
In the extracellular stage, linear chains of peptidoglycans are cross linked by membrane-bound transpeptidases. This stage is inhibited by β-lactams.

β-Lactam Antibiotics

β-Lactam antibiotics, including Penicillins, Cephalosporins, Monobactams, and Carbapenems, inhibit bacterial cell wall synthesis by blocking the cross linking of peptide chains during peptidoglycan biosynthesis.
They act by inhibiting transpeptidases, which are a type of Penicillin Binding Protein, by mimicking the D-alanyl-D-alanine residues and reacting covalently with the transpeptidase.
β-Lactam antibiotics cause the cell to become deformed in shape and eventually burst due to the combined action of a weakened cell wall, high internal osmotic pressure, and uncontrolled activity of autolytic enzymes in the cell wall.

Penicillins

Penicillins are a type of β-lactam antibiotic that includes natural penicillins, penicillinase-resistant penicillins, aminopenicillins, and extended-spectrum penicillins.
Natural penicillins, such as penicillin G, are active against Gram-positive streptococci, staphylococci, and some Gram-negative bacteria.
Penicillinase-resistant penicillins, such as methicillin, are active against β-lactamase-producing bacteria that inactivate most penicillin antibiotics.
Aminopenicillins, such as ampicillin and amoxicillin, are effective against a wider range of bacteria and have better oral absorption.
Extended-spectrum penicillins, such as mezlocillin, piperacillin, and ticarcillin, are active against a wider range of Gram-negative bacteria.

Glycopeptides - Vancomycin

Vancomycin is a glycopeptide antibiotic that inhibits cell wall biosynthesis and is bactericidal against Gram-positive bacterial pathogens.
It works by binding to the end of the peptide chain of cell wall precursors, creating a structural blockage that prevents the cell wall subunits from being incorporated into the growing peptidoglycan structure.
Vancomycin is not active against Gram-negative bacteria due to its inability to penetrate the protective outer membrane.

Inhibitors of Protein Synthesis (Translation)

Proteins are made up of individual units of amino acids, with instructions for making proteins found in the DNA.
Protein synthesis requires the input of mRNA template, ribosomes, tRNAs, and various enzymatic factors.
Inhibitors of protein synthesis include aminoglycosides, tetracyclines, macrolides, lincosamides, chloramphenicol, and oxazolidinones.

Classification of Antimicrobial Agents

Antimicrobial agents can be classified based on type of action, source, spectrum of activity, chemical structure, and function (mode of action).
Bactericidal agents destroy bacteria by targeting the cell wall or cell membrane, while bacteriostatic agents slow or inhibit the growth of bacteria.

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Description

This quiz covers the basics of antimicrobial chemotherapy, including classification, mechanism of action, and chemical structures of antimicrobial agents.