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:
Cultivation – Bacteria grown in controlled media.
Harvesting – Cells collected via centrifugation/filtration.
Inactivation – Killed using heat or chemicals (e.g., formaldehyde).
Purification – Removes residual media/toxins.
Formulation – Mixed with stabilizers/adjuvants (e.g., aluminum salts).
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:
Strain Selection – A naturally weak or genetically modified attenuated strain is chosen.
Cultivation – Grown under strict aseptic conditions.
Harvesting & Stabilization – Bacteria are washed and suspended in stabilizers.
Quality Control – Ensures attenuation, purity, and viability.
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:
Antigen Isolation – Extract bacterial polysaccharides, proteins, or toxins.
Purification – Ensures high purity (e.g., capsular polysaccharides from S. pneumoniae).
Conjugation (if needed) – Polysaccharides linked to protein carriers (e.g., diphtheria toxoid) for stronger immunity.
Formulation & Filling – Combined with adjuvants and tested for sterility, potency, and purity.
Examples:
Pneumococcal conjugate vaccine (PCV13).
Haemophilus influenzae type b (Hib) conjugate vaccine.
