Question

Which of the following is a mismatch?

• A. Live R strain - Non-virulent
• B. Heat-killed R strain - Virulent
• C. Live S strain - Pathogenic
• D. Heat-killed S strain - Non-pathogenic

Answer 1

The correct option is B

Heat-killed R strain - Virulent

Griffith considered two different strains of the bacterium Streptococcus pneumoniae - S strain and R strain. The former is pathogenic/virulent and can cause the disease, while the latter is non-pathogenic/non-virulent and cannot cause the disease. Heat-killed S strain bacteria however, lose their virulence and become non-pathogenic. R strain bacteria in general, don’t need to be heat-killed as they are already non-pathogenic.