6 Microbial Growth Antibiotics 1-31-11

6 Microbial Growth Antibiotics 1-31-11 - Antibiotics...

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Unformatted text preview: Antibiotics Antibiotics Sections 27.1-27.7 What are Antibiotics? What are Antibiotics? • A molecule that can kill or inhibit the growth of bacteria • Types of antibiotics – Natural products (from bacteria, fungi) – Synthetic (from chemists) – Semi-synthetic – natural products chemically modified in the laboratory • Effects of antibiotics – Bactericidal (kill bacteria) – Bacteriostatic (inhibit their growth, but does not kill bacteria) What are Antibiotics? What are Antibiotics? • Antibiotics have selective toxicity – Affect selected bacteria, but not the eukaryotic host cells – Usually attack a unique component of bacterial physiology (missing or different from eukaryotic physiology) • DNA synthesis • RNA synthesis • Protein synthesis • Peptidoglycan synthesis Examples of Antibiotics Examples of Antibiotics • DNA synthesis in bacteria requires DNA gyrase – Quinolone binds to DNA gyrase, prevents supercoiling and packaging of DNA during cell division • RNA synthesis in bacteria requires RNA polymerase – Rifampin binds to and inhibits bacterial RNA polymerase activity Figure 27.14 naladixic acid quinolone norfloxacin ciprofloxacin rifampin rifampin and RNA polymerase Examples of Antibiotics Examples of Antibiotics • Protein synthesis in bacteria requires 30S + 50S ribosomal subunits = 70S ribosomes – – binds 30S ribosomal subunit – Erythromycin – binds 50S ribosomal subunit Figure 27.15 Note: Eukaryotes have 40S + 60S ribosomal subunits = 80S ribosomes Examples of Antibiotics Examples of Antibiotics • Peptidoglycan (PG) synthesis – PG is only found in bacterial cell walls – If PG synthesis is affected, the cell wall will not be as strong, and the cell will lyse due to osmosis (killing requires the cell to be growing) – Penicillin Figure 5.33 Figure 5.34 Synthesis of Peptidoglycan – Synthesis of Peptidoglycan – A reminder of where it is located A reminder of where it is located Gram + Gram PG Cytoplasm Cytoplasm Synthesis of Peptidoglycan – Synthesis of Peptidoglycan – A reminder of what it A reminder of what it looks like looks like E. coli PG NAG NAM Peptide Staphylococcus aureus PG Pentaglycine Synthesis of Peptidoglycan Synthesis of Peptidoglycan 1-2) In the cytoplasm , NAM linked to peptide 3) NAM-peptide binds bactoprenol in CM 4) NAG linked to NAM- peptide M M + M M G Figure 27.7 Bactoprenol 5) NAG-NAM-peptide transported across CM to the outside by bactoprenol 6) NAG-NAM-peptides linked together to form long chains (glycan strands or peptidoglycan strands or PG strands) Synthesis of Peptidoglycan Synthesis of Peptidoglycan M G M G M G M G Figure 27.7 v Synthesis of Peptidoglycan Synthesis of Peptidoglycan M G M G M G 7) Glycan strands crosslinked together M G M G M G M G M G M G M G M G M G Figure 27.7 Note: different types of peptide crosslinks are shown here Antibiotics that inhibit PG Antibiotics that inhibit PG synthesis synthesis • Fosfomycin – inhibits formation of NAM-peptide...
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6 Microbial Growth Antibiotics 1-31-11 - Antibiotics...

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