The Search for Wonder Drugs: Antibiotics

Ancient Use of Antibiotics
- Among the possessions of Ötzi, the 5000 year-old mummified Ice Man, were mushrooms with known antibiotic properties.
- Ancient cultures worldwide recognized molds as valuable for treating infections.
Infections Before Antibiotics
- Prior to the discovery of antibiotics, infections were a significant cause of mortality.
- Common injuries like abrasions and skin wounds could lead to gangrene.
- The understanding of infectious diseases was limited, resulting in high mortality rates.

Pyocyanin
- Isolated in 1888 from Pseudomonas aeruginosa, one of the first antibiotics discovered.
Penicillin Discovery
- Alexander Fleming discovered the Penicillium fungus, which became the source of penicillin.
- Howard Florey and Ernst Chain developed a viable drug from this fungus.
Early Production of Penicillin
- Initial yields of penicillin were low; however, research and selection methods markedly improved yields.
- Andrew Moyer developed mass production methods for penicillin.
- John Sheehan uncovered the molecular structure of penicillin.
- Early forms of penicillin were mixtures, but penicillin G was identified as the most effective variant.
Discovery of Streptomycin
- Selman Waksman discovered streptomycin, the first antibiotic effective against tuberculosis (TB).

Sources of Antibiotics
- Penicillin was the first useful antibiotic, yet most antibiotics currently are derived from bacteria.
- The search for new antibiotics involves testing for effects on bacteria, but useful compounds are rare to find.

Essential Requirements for Antibiotics
- Yield: Must be high enough for effective treatment.
- Toxicity: Should have low toxicity and side effects.
- Stability: High shelf life for storage and usage.
- Therapeutic Duration: The drug must remain effective in the body long enough to eliminate the infection.
- Drug Resistance: Must consider the speed at which antibiotic resistance develops.

Antibiotics by Organism
- Distribution of known antibiotics is as follows:
- Streptomyces: 58%
- Other bacteria: 9%
- Fungi, algae, lichens, mosses: 19%
- Higher plants: 14% (note: no commercial antibiotics are derived from higher plants).
- Both Penicillium and Streptomyces are responsible for nearly all medically important antibiotics.

Mechanism of Action
- Penicillin inhibits bacterial cell wall growth, causing bacteria to swell and potentially burst due to osmotic pressure.
Model of Bacterial Cell Walls
- Diagram showing structural differences:
- Gram-positive Bacteria: Thick peptidoglycan layer.
- Gram-negative Bacteria: Thin peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharides.

Types and Activities
- Various clinically important antibiotics include:
- Penicillin: Produced by Penicillium chrysogenum; effective against Gram-positive bacteria by inhibiting wall synthesis.
- Cephalosporin: Produced by Cephalosporium acremonium; broad-spectrum activity, also targets wall synthesis.
- Streptomycin: From Streptomyces griseus; targets protein synthesis in Gram-negative bacteria.
- Vancomycin: From Streptomyces orientalis; inhibits protein synthesis in Gram-positive bacteria.
- Rifamycin: From Streptomyces mediterranei; aimed at tuberculosis with protein synthesis inhibition.

Widespread Resistance
- Antibiotic resistance is now common among many bacterial strains, making treatment increasingly difficult.
- Antibiotics create selection pressures favoring the survival of resistant bacteria, leading to higher resistant populations.
Mechanisms of Gene Transfer for Resistance
- Unrelated bacterial species can share genes, accelerating the spread of antibiotic resistance through mechanisms such as:
- Transformation: Uptake of free DNA from lysed bacteria.
- Conjugation: Direct transfer of DNA between bacteria via plasmids.
- Transduction: Transfer of genetic material by a virus.
Historical Context of Antibiotic Research
- In the 1980s, many drug companies abandoned antibiotic research due to:
- Saturated market with available effective antibiotics.
- Low financial return on investment for antibiotic development, turning instead to AIDS and antiviral drugs.

Growing Resistance
- Resistance rates have risen sharply, with an increase in multi-drug resistant strains observed in bacterial species, including E. coli and Klebsiella pneumoniae.
- 65% of E. coli are resistant to fluoroquinolones, and many other common antibiotics show similar trends.

Death Rates Related to Resistance
- 33,000 annual deaths in Europe attributed to antibiotic-resistant infections.
- Approximately 1.2 million global deaths linked directly to antibiotic-resistant infections, leading to an additional 5 million deaths due to related complications.

Data on MDR-TB
- Increasing instances of multi-drug resistant tuberculosis (MDR-TB) reported globally, especially in areas with poor healthcare conditions.

Bacterial Evasion Strategies
- Bacteria develop mechanisms including:
- Enzymes that inactivate antibiotics.
- Pumps that expel antibiotics from their systems.
- Enhanced cell walls that prevent antibiotic entry.
- Modification of target structures to render antibiotics ineffective.

Factors Contributing to Resistance
- Antibiotic resistance emerges through various means, including:
- Over-prescription and inappropriate use of antibiotics.
- Patients not completing prescribed courses.
- Overuse in livestock and aquaculture.
- Poor hygiene and infection control in medical settings.

Agricultural Impact
- 80% of antibiotics are administered to livestock to promote growth and prevent disease, significantly contributing to the spread of antibiotic resistance.
- The improper use of antibiotics in food production can lead to increased bacterial resistance.

Joseph Lister
- Inspired by Louis Pasteur’s research, Lister acknowledged the significance of antiseptics in surgery.
Introduction of Listerine
- Listerine, created in 1879 by Joseph Lawrence, was inspired by Lister's work and formulated as a surgical antiseptic.
- Ingredients include eucalyptol, menthol, thymol, methyl salicylate, and alcohol.

Sources of Natural Antiseptics
- Various plants have been recognized for their antibacterial properties, including:
- Azadirachta indica (neem tree) – Contains numerous antimicrobial compounds.
- Melaleuca leucadendra – Produces oils with germicidal activity for surgery and hygiene products.
- Allium sativum (garlic) – Notably effective in traditional and modern remedies against bacteria.

Plants and herbal remedies are being increasingly explored for their potential antibacterial properties, such as:
- Phyllanthus emblica L. (Amla)
- Terminalia arjuna (Arjuna)
- Various spices also demonstrate effectiveness against bacterial strains, emphasizing the importance of botanical research in the battle against resistance.