Antibiotics and Their Impact on Bacteria (Module 2)

1. What are antibiotics?

Antibiotics are chemical compounds that inhibit or kill bacteria, aiding in the treatment of bacterial infections.

Note:

• Antibiotics are ineffective against viruses, fungi, and parasites.

• Overusing antibiotics can lead to drug resistance, making it harder to treat infections.

2. Origin and Mechanism of Action of Antibiotics:

• Origin:

• Natural antibiotics: Extracted from fungi, bacteria, or other organisms. For example, penicillin is extracted from the Penicillium notatum fungus.

• Semi-synthetic antibiotics: Created by modifying the chemical structure of natural antibiotics. For example, methicillin is a semi-synthetic derivative of penicillin.

• Synthetic antibiotics: Entirely synthesized using chemical methods. For example, ciprofloxacin.

• Mechanism of Action:

• Antibiotics specifically target structural molecules or biochemical processes within bacteria, inhibiting or killing them.

• They are generally not toxic to humans (when used at appropriate doses and under medical supervision).

3. Classification of Antibiotics:

a) By Spectrum of Action:

• Broad-spectrum: Effective against a wide range of bacteria, e.g., tetracycline, doxycycline.

• Narrow-spectrum: Effective against one or a few specific types of bacteria, e.g., penicillin G, vancomycin.

b) By Mode of Action:

• Bacteriostatic: Inhibit bacterial cell multiplication, e.g., tetracycline, erythromycin.

• Bactericidal: Irreversibly destroy bacterial cell functions, e.g., penicillin, cephalosporin.

c) By Chemical Structure:

• Classification based on chemical structure helps in choosing appropriate antibiotics, finding suitable replacements, or combining antibiotics effectively in treatment.

4. Major Groups of Antibiotics and Their Impact on Bacteria:

a) Antibiotics Targeting Bacterial Cell Wall Synthesis:

• Beta-lactam group:

• Penicillin: penicillin G, penicillin V, amoxicillin, methicillin.

• Cephalosporin: cephalexin, cefaclor, ceftriaxone.

• Glycopeptide: vancomycin.

b) Antibiotics Inhibiting Protein Synthesis:

• Aminoglycoside: gentamicin, tobramycin.

• Tetracycline: tetracycline, doxycycline.

• Macrolide: erythromycin, azithromycin.

c) Antibiotics Inhibiting Nucleic Acid Synthesis:

• Quinolone: ciprofloxacin, levofloxacin.

• Rifamycin: rifampicin.

5. Some Common Antibiotics:

a) Penicillin:

• Penicillin G (benzyl penicillin):

• Effective against cocci, Gram-positive bacilli, spirochetes (except penicillinase-producing cocci, Gram-negative bacilli).

• Degraded by gastric juices, so it’s not administered orally.

• Penicillin V: Similar activity to penicillin G but not degraded by gastric juices.

• Penicillin A (aminopenicillin/ampicillin/amoxicillin):

• Broader spectrum than penicillin G.

• Effective against Gram-negative bacilli (Haemophilus, E.coli, Salmonella, Shigella).

• Susceptible to beta-lactamase.

• Penicillin M (methicillin/oxacillin/nafcillin):

• Penicillin derivatives resistant to penicillinase.

• Used primarily for staphylococcal infections.

b) Cephalosporin:

• Cephalosporin:

• Semi-synthetically produced from cephalosporin C (a natural antibiotic produced by the Cephalosporium fungus).

• Broader spectrum than penicillin, resistant to penicillinase.

• Many derivatives exist with varying spectra of action.

Note:

• Drug Resistance: Bacteria can adapt and become resistant to antibiotics, rendering the drugs ineffective.

• Appropriate Antibiotic Selection: Choosing the right antibiotic requires bacterial identification through culture and antibiotic sensitivity testing.

• Antibiotic Use as Prescribed by Doctors: Avoid self-medicating with antibiotics to prevent drug resistance and dangerous side effects.

• Dosage and Duration of Treatment: Antibiotics should be used at the correct dose and for the prescribed duration to ensure treatment effectiveness and minimize side effects.

6. Conclusion:

Antibiotics are crucial tools in treating bacterial infections. However, rational antibiotic use is essential to maintain treatment effectiveness and prevent drug resistance.