Preparation of Bacterial Vaccines

Definition

• Bacterial vaccines contain killed or attenuated (weakened) bacteria or their components to stimulate an immune response without causing disease.

• Bacterial vaccines protect against bacterial infections and are categorized into:

  • Killed (Inactivated) Vaccines – Contain dead bacteria (e.g., Whole-cell pertussis, Typhoid vaccine).

  • Live Attenuated Vaccines – Contain weakened bacteria (e.g., BCG vaccine).

  • Subunit/Conjugate Vaccines – Contain specific bacterial components (e.g., PCV13, Hib vaccine).

General Method of Preparation

1) Killed (Inactivated) Bacterial Vaccines

Steps:

1. Cultivation – Bacteria grown in controlled media.

2. Harvesting – Cells collected via centrifugation/filtration.

3. Inactivation – Killed using heat or chemicals (e.g., formaldehyde).

4. Purification – Removes residual media/toxins.

5. Formulation – Mixed with stabilizers/adjuvants (e.g., aluminum salts).

6. Filling & Lyophilization (optional) – Packaged in vials, sometimes freeze-dried.

Examples:

• Whole-cell pertussis vaccine (older-generation component of DTP).

• Typhoid vaccine (inactivated, injectable form).

2) Live Attenuated Bacterial Vaccines

Steps:

1. Strain Selection – A naturally weak or genetically modified attenuated strain is chosen.

2. Cultivation – Grown under strict aseptic conditions.

3. Harvesting & Stabilization – Bacteria are washed and suspended in stabilizers.

4. Quality Control – Ensures attenuation, purity, and viability.

5. Formulation & Packaging – Often freeze-dried (lyophilized) for stability.

Examples:

• BCG vaccine (for tuberculosis) is a live attenuated strain of Mycobacterium bovis.

3) Subunit / Conjugate Bacterial Vaccines

Steps:

1. Antigen Isolation – Extract bacterial polysaccharides, proteins, or toxins.

2. Purification – Ensures high purity (e.g., capsular polysaccharides from S. pneumoniae).

3. Conjugation (if needed) – Polysaccharides linked to protein carriers (e.g., diphtheria toxoid) for stronger immunity.

4. Formulation & Filling – Combined with adjuvants and tested for sterility, potency, and purity.

Examples:

• Pneumococcal conjugate vaccine (PCV13).

• Haemophilus influenzae type b (Hib) conjugate vaccine.