Comment on antimicrobial drug resistance as a global health challenge (20%). Write an essay on validating arylamine N-acetyl transferase (NAT) as a novel therapeutic target in Mycobacterium tuberculosis (80%).

Short Answer

Pro-drug Activation in Bacterial Endogenous Metabolism and Mechanisms of Antibiotic Resistance

Introduction

Antibiotic therapy does not always rely on drugs being active in their original form. In several important cases, compounds are administered as inactive or weakly active pro-drugs and are later converted into active molecules inside bacterial cells. This strategy allows selective targeting of bacterial metabolic processes. Alongside this, antibiotic resistance has become a major clinical issue, driven by genetic adaptation and physiological defence systems such as reduced membrane permeability and active efflux. This essay explains both concepts in detail, using named examples and focusing on how bacteria survive antibiotic pressure.

Pro-drug Targeting of Endogenous Bacterial Metabolism

A pro-drug is a compound that requires biochemical conversion inside the target organism to become pharmacologically active. In bacteria, this often involves bacterial enzymes linked to essential metabolic pathways.

Named Example: Isoniazid in Mycobacterium tuberculosis

A key example is isoniazid, used in tuberculosis treatment. Isoniazid is not active until it enters Mycobacterium tuberculosis, where it is activated by the bacterial catalase-peroxidase enzyme KatG.

Once activated, it forms a reactive intermediate that inhibits InhA (enoyl-acyl carrier protein reductase), an essential enzyme in mycolic acid synthesis. Mycolic acids are vital components of the mycobacterial cell wall, and without them, the bacterium loses structural integrity and dies.

How the mechanism links to endogenous metabolism

The key point is that isoniazid disrupts a bacterial internal metabolic pathway rather than attacking an external structure. The process can be summarised as:

Isoniazid (pro-drug)
 ↓ (KatG activation)
Reactive isoniazid metabolite
 ↓
Inhibition of InhA enzyme
 ↓
Blocked mycolic acid synthesis
 ↓
Cell wall failure and bacterial death

Other relevant examples

• Pyrazinamide → converted to pyrazinoic acid inside M. tuberculosis, disrupting membrane energetics and fatty acid synthesis.
• Metronidazole → activated in anaerobic bacteria by reduction, producing free radicals that damage DNA.

These examples show how pro-drugs exploit bacterial metabolic activity to generate toxicity internally rather than externally.

Development of Antibiotic Resistance in Bacteria

Antibiotic resistance develops through both genetic change and selective pressure. When antibiotics are used, susceptible bacteria are killed while resistant variants survive and multiply.

Main mechanisms of resistance development

Bacteria acquire resistance through:

• Spontaneous mutations in chromosomal DNA
• Horizontal gene transfer via plasmids, transposons, or bacteriophages
• Selective pressure from antibiotic overuse or incomplete treatment

Over time, resistant strains dominate bacterial populations.