Ribosomal RNA Function and Mechanism of Action

Ribosomal RNA Function

• 30S and 50S ribosomal subunits are key targets
• 30S subunit is involved in decoding of mRNA
• 50S subunit is involved in linking amino acids together
• Both subunits are involved in translocating the translation machine

Mechanism of Action

• Bacterial protein synthesis is the target
• Two sites involved: P site (peptidyl) and A site (aminoacyl)
• Most agents target either 50S or 30S subunits and are selective to bacteria
• Exceptions: Chloramphenicol has activity against protozoan parasites
• Inhibiting organellar protein synthesis
• Complete inhibition of protein synthesis is not necessary to kill bacteria
• Most agents are bacteriostatic, except Aminoglycosides

Mechanisms of Resistance

• Unique to each class of agents
• No specific details provided

Fluoroquinolones

• Quinolone structure with fluorine at position 6
• Structural changes at positions 1, 5, 7, and 8
• Inhibit DNA synthesis by changing DNA configuration, not primary sequence
• Targets topoisomerase II (DNA gyrase) and topoisomerase IV
• Topoisomerase II: relaxes supercoiled DNA in Gram-negative bacteria
• Topoisomerase IV: involved in cell division in Gram-positive bacteria
• Normal process: conformational change, ATP required, DNA segment "locked", and religated

Mechanisms of Resistance to Fluoroquinolones

• Chromosomal mutations in genes encoding topoisomerase II or IV
• Alterations in membrane porins
• Alterations in efflux pumps
• Generally confers cross-resistance in class

Folic Acid Antagonists

• Targets PABA analogues and folate analogues
• PABA analogues (Sulfonamides) competitively inhibit Dihydropteroate synthetase
• Folate analogues competitively inhibit dihydrofolate reductase
• Prevents folic acid formation and conversion to active coenzyme form

Mechanisms of Resistance to Folic Acid Antagonists

• Plasmid transfer or random mutations
• Altered dihydropteroate synthetase or dihydrofolate reductase
• Decreased permeability to sulfonamide
• Enhanced production of PABA
• Overproduction of dihydrofolate reductase

Ribosomal RNA Function

• 30S and 50S ribosomal subunits are key targets
• 30S subunit is involved in decoding of mRNA
• 50S subunit is involved in linking amino acids together
• Both subunits are involved in translocating the translation machine

Mechanism of Action

• Bacterial protein synthesis is the target
• Two sites involved: P site (peptidyl) and A site (aminoacyl)
• Most agents target either 50S or 30S subunits and are selective to bacteria
• Exceptions: Chloramphenicol has activity against protozoan parasites
• Inhibiting organellar protein synthesis
• Complete inhibition of protein synthesis is not necessary to kill bacteria
• Most agents are bacteriostatic, except Aminoglycosides

Mechanisms of Resistance

• Unique to each class of agents
• No specific details provided

Fluoroquinolones

• Quinolone structure with fluorine at position 6
• Structural changes at positions 1, 5, 7, and 8
• Inhibit DNA synthesis by changing DNA configuration, not primary sequence
• Targets topoisomerase II (DNA gyrase) and topoisomerase IV
• Topoisomerase II: relaxes supercoiled DNA in Gram-negative bacteria
• Topoisomerase IV: involved in cell division in Gram-positive bacteria
• Normal process: conformational change, ATP required, DNA segment "locked", and religated

Mechanisms of Resistance to Fluoroquinolones

• Chromosomal mutations in genes encoding topoisomerase II or IV
• Alterations in membrane porins
• Alterations in efflux pumps
• Generally confers cross-resistance in class

Folic Acid Antagonists

• Targets PABA analogues and folate analogues
• PABA analogues (Sulfonamides) competitively inhibit Dihydropteroate synthetase
• Folate analogues competitively inhibit dihydrofolate reductase
• Prevents folic acid formation and conversion to active coenzyme form

Mechanisms of Resistance to Folic Acid Antagonists

• Plasmid transfer or random mutations
• Altered dihydropteroate synthetase or dihydrofolate reductase
• Decreased permeability to sulfonamide
• Enhanced production of PABA
• Overproduction of dihydrofolate reductase

Ribosomal RNA Function

• 30S and 50S ribosomal subunits are key targets
• 30S subunit is involved in decoding of mRNA
• 50S subunit is involved in linking amino acids together
• Both subunits are involved in translocating the translation machine

Mechanism of Action

• Bacterial protein synthesis is the target
• Two sites involved: P site (peptidyl) and A site (aminoacyl)
• Most agents target either 50S or 30S subunits and are selective to bacteria
• Exceptions: Chloramphenicol has activity against protozoan parasites
• Inhibiting organellar protein synthesis
• Complete inhibition of protein synthesis is not necessary to kill bacteria
• Most agents are bacteriostatic, except Aminoglycosides

Mechanisms of Resistance

• Unique to each class of agents
• No specific details provided

Fluoroquinolones

• Quinolone structure with fluorine at position 6
• Structural changes at positions 1, 5, 7, and 8
• Inhibit DNA synthesis by changing DNA configuration, not primary sequence
• Targets topoisomerase II (DNA gyrase) and topoisomerase IV
• Topoisomerase II: relaxes supercoiled DNA in Gram-negative bacteria
• Topoisomerase IV: involved in cell division in Gram-positive bacteria
• Normal process: conformational change, ATP required, DNA segment "locked", and religated

Mechanisms of Resistance to Fluoroquinolones

• Chromosomal mutations in genes encoding topoisomerase II or IV
• Alterations in membrane porins
• Alterations in efflux pumps
• Generally confers cross-resistance in class

Folic Acid Antagonists

• Targets PABA analogues and folate analogues
• PABA analogues (Sulfonamides) competitively inhibit Dihydropteroate synthetase
• Folate analogues competitively inhibit dihydrofolate reductase
• Prevents folic acid formation and conversion to active coenzyme form

Mechanisms of Resistance to Folic Acid Antagonists

• Plasmid transfer or random mutations
• Altered dihydropteroate synthetase or dihydrofolate reductase
• Decreased permeability to sulfonamide
• Enhanced production of PABA
• Overproduction of dihydrofolate reductase

Ribosomal RNA Function

• 30S and 50S ribosomal subunits are key targets
• 30S subunit is involved in decoding of mRNA
• 50S subunit is involved in linking amino acids together
• Both subunits are involved in translocating the translation machine

Mechanism of Action

• Bacterial protein synthesis is the target
• Two sites involved: P site (peptidyl) and A site (aminoacyl)
• Most agents target either 50S or 30S subunits and are selective to bacteria
• Exceptions: Chloramphenicol has activity against protozoan parasites
• Inhibiting organellar protein synthesis
• Complete inhibition of protein synthesis is not necessary to kill bacteria
• Most agents are bacteriostatic, except Aminoglycosides

Mechanisms of Resistance

• Unique to each class of agents
• No specific details provided

Fluoroquinolones

• Quinolone structure with fluorine at position 6
• Structural changes at positions 1, 5, 7, and 8
• Inhibit DNA synthesis by changing DNA configuration, not primary sequence
• Targets topoisomerase II (DNA gyrase) and topoisomerase IV
• Topoisomerase II: relaxes supercoiled DNA in Gram-negative bacteria
• Topoisomerase IV: involved in cell division in Gram-positive bacteria
• Normal process: conformational change, ATP required, DNA segment "locked", and religated

Mechanisms of Resistance to Fluoroquinolones

• Chromosomal mutations in genes encoding topoisomerase II or IV
• Alterations in membrane porins
• Alterations in efflux pumps
• Generally confers cross-resistance in class

Folic Acid Antagonists

• Targets PABA analogues and folate analogues
• PABA analogues (Sulfonamides) competitively inhibit Dihydropteroate synthetase
• Folate analogues competitively inhibit dihydrofolate reductase
• Prevents folic acid formation and conversion to active coenzyme form

Mechanisms of Resistance to Folic Acid Antagonists

• Plasmid transfer or random mutations
• Altered dihydropteroate synthetase or dihydrofolate reductase
• Decreased permeability to sulfonamide
• Enhanced production of PABA
• Overproduction of dihydrofolate reductase

Mechanism of Action

• Bacterial protein synthesis involves Ribosomal RNA (rRNA) that differs from other organisms.
• The 30S subunit is responsible for decoding mRNA.
• The 50S subunit links together amino acids to form a peptide chain.
• Both subunits (30S and 50S) are involved in translocating the translation machine.
• The ribosome has two sites: P “peptidyl” site and A “aminoacyl” site.
• The P “peptidyl” site contains the growing peptide chain.
• The A “aminoacyl” site binds incoming tRNA containing amino acids.

Mechanism of Action

• Bacterial protein synthesis involves Ribosomal RNA (rRNA) that differs from other organisms.
• The 30S subunit is responsible for decoding mRNA.
• The 50S subunit links together amino acids to form a peptide chain.
• Both subunits (30S and 50S) are involved in translocating the translation machine.
• The ribosome has two sites: P “peptidyl” site and A “aminoacyl” site.
• The P “peptidyl” site contains the growing peptide chain.
• The A “aminoacyl” site binds incoming tRNA containing amino acids.

Sites of Action

• Antibiotics target either 50S or 30S ribosomal subunits
• Most antibiotics are selective to bacteria, but not chloramphenicol
• Some antibiotics also show activity against protozoan and parasites

Mechanism of Action

• Antibiotics inhibit organellar protein synthesis
• Complete inhibition of protein synthesis does not kill bacteria
• Most antibiotics are bacteriostatic, except for aminoglycosides

Quinolone Structure and Mechanism of Action

• Quinolone structure features a fluorine atom at position 6
• Structural modifications occur at positions 1, 5, 7, and 8

Quinolone Structure and Mechanism of Action

• Quinolone structure features a fluorine atom at position 6
• Structural modifications occur at positions 1, 5, 7, and 8

Bacterial Protein Synthesis

• Provides the machinery for:
  • Decoding of mRNA (30S)
  • Linking together of the amino acids (50S)
  • Translocating of the translation machine (both subunits)
• Two sites:
  • P "peptidyl" site – contains the growing peptide chain
  • A "aminoacyl" site – binds incoming tRNA containing amino acids
• Sites of action:
  • Most target either 50S or 30S
  • Most are selective to bacteria
  • Exception: Chloramphenicol, also has activity against protozoan, parasites
• Inhibits organellar protein synthesis
• Complete inhibition of protein synthesis will not kill bacteria
• Most agents are bacteriostatic, except for Aminoglycosides

Fluoroquinolones

• Structure and Mechanism of action:
  • Bactericidal, Concentration-Dependent Killing, Post-antibiotic Effect
  • Key structural components:
    • Quinolone structure - Fluorine at position 6
    • Structural changes at 1, 5, 7, and 8 positions
• Mechanism of action:
  • Inhibition of DNA synthesis
  • Change the configuration of the DNA
  • Do not change the DNA’s primary sequence
• Sites of action:
  • Topoisomerase II (DNA gyrase)
    • Gram negatives, allows relaxation of supercoiled DNA
    • Inhibition results in supercoiling, preventing DNA replication
  • Topoisomerase IV – Role in cell division
    • Gram positives, allows for decatenation of replicated DNA
    • Inhibition prevents DNA replication
• Mechanisms of Resistance:
  • Chromosomal mutations in the genes that encode one or both enzymes
  • Alteration in the expression of membrane porins
  • Alteration in efflux pumps
  • Generally confers cross-resistance in class

Folic Acid Antagonists

• Mechanism of action:
  • Bacteriostatic, Time-Dependent Killing, Bactericidal when combined
  • Drug action targets:
    • Paraaminobenzoic Acid (PABA) analogues
    • Folate analogues
• Mechanism of action:
  • PABA analogues (Sulfonamides):
    • Competitively inhibit Dihydropteroate synthetase
    • Unique to bacteria
    • Prevents folic acid formation
  • Folate analogues:
    • Competitively inhibit dihydrofolate reductase
    • Higher affinity to bacterial reductase
    • Prevents conversion to active coenzyme form (Tetrahydrofolic acid)
• Mechanisms of Resistance:
  • Plasmid transfer or random mutations
  • Altered dihydropteroate synthetase or dihydrofolate reductase
  • Decreased permeability to sulfonamide
  • Enhanced production of PABA
  • Overproduction of dihydrofolate reductase

Sites of Action

• Topoisomerase II (DNA gyrase) is a site of action, specifically in Gram-negative bacteria
• It plays a crucial role in allowing the relaxation of supercoiled DNA, which is necessary for normal transcription and replication
• Inhibition of Topoisomerase II (DNA gyrase) results in supercoiling, which prevents DNA replication

Protein Synthesis Inhibitors

• Targets: 30S and 50S ribosomal subunits
• Mechanism of action:
  • Provides machinery for decoding of mRNA (30S) and linking of amino acids (50S)
  • Two sites: P "peptidyl" site (growing peptide chain) and A "aminoacyl" site (binds incoming tRNA containing amino acids)
• Sites of action:
  • Most target either 50S or 30S
  • Most are selective to bacteria
  • Exception: Chloramphenicol (also active against protozoan, parasites)
• Inhibit organellar protein synthesis
• Complete inhibition of protein synthesis will not kill bacteria
  • Most agents are bacteriostatic (Exception: Aminoglycosides)

Fluoroquinolones

• Structure:
  • Quinolone structure with fluorine at position 6
  • Structural changes at 1, 5, 7, and 8 positions
• Mechanism of action:
  • Inhibition of DNA synthesis
  • Change the configuration of the DNA
  • Do not change the DNA's primary sequence
• Sites of action:
  • Topoisomerase II (DNA gyrase)
    • Gram negatives: allows relaxation of supercoiled DNA necessary for normal transcription and replication
    • Inhibition results in supercoiling which prevents DNA replication
  • Topoisomerase IV - Role in cell division
    • Gram positives: allows for decatenation of replicated DNA into daughter cells
    • Inhibition prevents DNA replication
• Mechanisms of resistance:
  • Chromosomal mutations in genes that encode one or both enzymes
  • Alteration in expression of membrane porins
  • Alteration in efflux pumps
  • Generally confers cross-resistance in class

Folic Acid Antagonists

• Mechanism of action:
  • PABA analogues (Sulfonamides)
    • Competitively inhibit Dihydropteroate synthetase
    • Unique to bacteria
    • Prevents folic acid formation
  • Folate analogues
    • Competitively inhibit dihydrofolate reductase
    • Higher affinity to bacterial reductase
    • Prevents conversion to active coenzyme form (Tetrahydrofolic acid)
• Mechanisms of resistance:
  • Plasmid transfer or random mutations
  • Altered dihydropteroate synthetase or dihydrofolate reductase
  • Decreased permeability to sulfonamide
  • Enhanced production of PABA
  • Overproduction of dihydrofolate reductase

Mechanism of Action

• Bacterial protein synthesis:
  • Provides machinery for decoding of mRNA (30S) and linking together of amino acids (50S)
  • Translocating of the translation machine (both subunits)
• Two sites:
  • P "peptidyl" site – contains the growing peptide chain
  • A "aminoacyl" site – binds incoming tRNA containing amino acids

Key Targets in Ribosomal RNA Function

• 30S ribosomal subunit
• 50S ribosomal subunit

Sites of Action

• Most target either 50S or 30S
• Most are selective to bacteria
• Exception: Chloramphenicol
• Also some activity against protozoan, parasites
• Inhibit organellar protein synthesis
• Complete inhibition of protein synthesis will not kill bacteria
• Most agents are bacteriostatic (Exception: Aminoglycosides)

Fluoroquinolones

• Quinolone structure - Fluorine at position 6
• Structural changes at 1, 5, 7, and 8 positions
• Mechanism of action:
  • Inhibition of DNA synthesis
  • Change the configuration of the DNA
  • Do not change the DNA’s primary sequence
• Sites of action:
  • Topoisomerase II (DNA gyrase) - Gram negatives
    • Allows relaxation of supercoiled DNA necessary for normal transcription and replication
    • Inhibition results in supercoiling which prevents DNA replication
  • Topoisomerase IV - Gram positives
    • Allows for decatenation of replicated DNA into daughter cells
    • Inhibition prevents DNA replication
• Normal process for DNA gyrase:
  • Type II topoisomerase enzymes engage DNA
  • Conformational change in enzyme to “lock” DNA segment
  • Second segment of DNA is “locked” into place (ATP required)
  • Enzyme cuts both strands of the first DNA segment (nicking)
  • Second DNA segment passes through the enzyme
  • Changes the coiling of the DNA by 1
  • Second segment is released and first segment is religated and released

Mechanisms of Resistance

• Chromosomal mutations in the genes that encode one or both enzymes
• Alteration in the expression of membrane porins
• Alteration in efflux pumps
• Generally confers cross-resistance in class

Folic Acid Antagonists

• Mechanism of action:
  • PABA analogues (Sulfonamides) - competitively inhibit dihydropteroate synthetase
  • Folate analogues - competitively inhibit dihydrofolate reductase
• Sites of action:
  • PABA analogues (Sulfonamides) - unique to bacteria
  • Folate analogues - higher affinity to bacterial reductase
• Mechanisms of Resistance:
  • Plasmid transfer or random mutations
  • Altered dihydropteroate synthetase or dihydrofolate reductase
  • Decreased permeability to sulfonamide
  • Enhanced production of PABA
  • Overproduction of dihydrofolate reductase

Mechanism of Action

• Bacterial protein synthesis:
  • Provides machinery for decoding of mRNA (30S) and linking together of amino acids (50S)
  • Translocating of the translation machine (both subunits)
• Two sites:
  • P "peptidyl" site – contains the growing peptide chain
  • A "aminoacyl" site – binds incoming tRNA containing amino acids

Key Targets in Ribosomal RNA Function

• 30S ribosomal subunit
• 50S ribosomal subunit

Sites of Action

• Most target either 50S or 30S
• Most are selective to bacteria
• Exception: Chloramphenicol
• Also some activity against protozoan, parasites
• Inhibit organellar protein synthesis
• Complete inhibition of protein synthesis will not kill bacteria
• Most agents are bacteriostatic (Exception: Aminoglycosides)

Fluoroquinolones

• Quinolone structure - Fluorine at position 6
• Structural changes at 1, 5, 7, and 8 positions
• Mechanism of action:
  • Inhibition of DNA synthesis
  • Change the configuration of the DNA
  • Do not change the DNA’s primary sequence
• Sites of action:
  • Topoisomerase II (DNA gyrase) - Gram negatives
    • Allows relaxation of supercoiled DNA necessary for normal transcription and replication
    • Inhibition results in supercoiling which prevents DNA replication
  • Topoisomerase IV - Gram positives
    • Allows for decatenation of replicated DNA into daughter cells
    • Inhibition prevents DNA replication
• Normal process for DNA gyrase:
  • Type II topoisomerase enzymes engage DNA
  • Conformational change in enzyme to “lock” DNA segment
  • Second segment of DNA is “locked” into place (ATP required)
  • Enzyme cuts both strands of the first DNA segment (nicking)
  • Second DNA segment passes through the enzyme
  • Changes the coiling of the DNA by 1
  • Second segment is released and first segment is religated and released

Mechanisms of Resistance

• Chromosomal mutations in the genes that encode one or both enzymes
• Alteration in the expression of membrane porins
• Alteration in efflux pumps
• Generally confers cross-resistance in class

Folic Acid Antagonists

• Mechanism of action:
  • PABA analogues (Sulfonamides) - competitively inhibit dihydropteroate synthetase
  • Folate analogues - competitively inhibit dihydrofolate reductase
• Sites of action:
  • PABA analogues (Sulfonamides) - unique to bacteria
  • Folate analogues - higher affinity to bacterial reductase
• Mechanisms of Resistance:
  • Plasmid transfer or random mutations
  • Altered dihydropteroate synthetase or dihydrofolate reductase
  • Decreased permeability to sulfonamide
  • Enhanced production of PABA
  • Overproduction of dihydrofolate reductase

Normal Process of DNA Gyrase

• Type II topoisomerase enzymes engage with DNA
• A conformational change occurs in the enzyme, enabling it to "lock" a DNA segment in place
• A second segment of DNA is "locked" into place, requiring ATP
• The enzyme cuts both strands of the first DNA segment through a process called nicking
• The second DNA segment passes through the enzyme, changing the coiling of the DNA by 1
• The second segment is released, and the first segment is religated and released

Normal Process of DNA Gyrase

• Type II topoisomerase enzymes engage with DNA
• A conformational change occurs in the enzyme, enabling it to "lock" a DNA segment in place
• A second segment of DNA is "locked" into place, requiring ATP
• The enzyme cuts both strands of the first DNA segment through a process called nicking
• The second DNA segment passes through the enzyme, changing the coiling of the DNA by 1
• The second segment is released, and the first segment is religated and released

Mechanisms of Resistance

• Chromosomal mutations occur in genes that encode one or both enzymes, leading to resistance.
• Alterations in the expression of membrane porins contribute to resistance.
• Alterations in efflux pumps also play a role in resistance.
• This type of resistance generally confers cross-resistance within a class.

Mechanisms of Resistance

• Chromosomal mutations occur in genes that encode one or both enzymes, leading to resistance.
• Alterations in the expression of membrane porins contribute to resistance.
• Alterations in efflux pumps also play a role in resistance.
• This type of resistance generally confers cross-resistance within a class.

Mechanism of Action

• Sulfonamides are bacteriostatic, but can be bactericidal when combined with other drugs
• They work by targeting two main drug action targets: Paraaminobenzoic Acid (PABA) analogues and Folate analogues

PABA Analogues (Sulfonamides)

• Competitively inhibit Dihydropteroate synthetase, a unique enzyme found only in bacteria
• Inhibition prevents folic acid formation, which is essential for bacterial growth and survival

Folate Analogues

• Competitively inhibit dihydrofolate reductase, an enzyme that plays a crucial role in folic acid synthesis
• Folate analogues have a higher affinity for bacterial dihydrofolate reductase compared to human enzymes
• Inhibition prevents the conversion of dihydrofolic acid to tetrahydrofolic acid, the active coenzyme form necessary for bacterial growth

Mechanisms of Resistance

• Bacteria acquire resistance to sulfonamides through plasmid transfer or random mutations.
• Altered dihydropteroate synthetase or dihydrofolate reductase enzymes reduce the effectiveness of sulfonamides.
• Decreased permeability to sulfonamides prevents the antibiotic from reaching its target site.
• Enhanced production of PABA (para-aminobenzoic acid) competes with sulfonamides, reducing their antibacterial activity.
• Overproduction of dihydrofolate reductase, an enzyme essential for bacterial metabolism, allows bacteria to counteract the effects of sulfonamides.

Mechanisms of Resistance

• Bacteria acquire resistance to sulfonamides through plasmid transfer or random mutations.
• Altered dihydropteroate synthetase or dihydrofolate reductase enzymes reduce the effectiveness of sulfonamides.
• Decreased permeability to sulfonamides prevents the antibiotic from reaching its target site.
• Enhanced production of PABA (para-aminobenzoic acid) competes with sulfonamides, reducing their antibacterial activity.
• Overproduction of dihydrofolate reductase, an enzyme essential for bacterial metabolism, allows bacteria to counteract the effects of sulfonamides.

Mechanisms of Resistance

• Bacteria acquire resistance to sulfonamides through plasmid transfer or random mutations.
• Altered dihydropteroate synthetase or dihydrofolate reductase enzymes reduce the effectiveness of sulfonamides.
• Decreased permeability to sulfonamides prevents the antibiotic from reaching its target site.
• Enhanced production of PABA (para-aminobenzoic acid) competes with sulfonamides, reducing their antibacterial activity.
• Overproduction of dihydrofolate reductase, an enzyme essential for bacterial metabolism, allows bacteria to counteract the effects of sulfonamides.

Mechanisms of Resistance

• Bacteria acquire resistance to sulfonamides through plasmid transfer or random mutations.
• Altered dihydropteroate synthetase or dihydrofolate reductase enzymes reduce the effectiveness of sulfonamides.
• Decreased permeability to sulfonamides prevents the antibiotic from reaching its target site.
• Enhanced production of PABA (para-aminobenzoic acid) competes with sulfonamides, reducing their antibacterial activity.
• Overproduction of dihydrofolate reductase, an enzyme essential for bacterial metabolism, allows bacteria to counteract the effects of sulfonamides.