The Bacille Calmette-Guerin (BCG) vaccine strain currently used worldwide was derived from which parent organism?
- A Mycobacterium tuberculosis attenuated by chemical mutagenesis
- B Mycobacterium bovis attenuated by serial subculture over 13 years ✓
- C Mycobacterium avium attenuated by heat killing
- D Mycobacterium africanum selected from a human sputum isolate
Correct answer: B. Mycobacterium bovis attenuated by serial subculture over 13 years
Explanation
Calmette and Guerin derived BCG from a virulent strain of Mycobacterium bovis obtained from a cow with tuberculous mastitis. They maintained it through approximately 239 serial passages on bile-potato medium over 13 years (1908 to 1921) until it lost virulence while retaining immunogenicity. It remains a live attenuated vaccine. Heat-killed organisms cannot replicate and were never the basis of BCG, and the strain is of bovine, not human, origin.
Reference: Park Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.