This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
All are true about streptococcus except : 
Select and explain. 
A. M-protein is responsible for production of mucoid colonies, B. M- protein is responsible for virulence, C. Mucoid colonies are virulent, D. No resistance to penicillin has been reported
A: M-protein is responsible for production of mucoid colonies
Answer: A: M-protein is responsible for production of mucoid colonies 
Explanation: “Mucoid colonies are due to production of capsule of hyaluronic acid not due to M protein.”
Harrison 17/e, p 882
Growth characteristic of Strep. pyogenes :

On blood agar virulent stains forms matt or mucoid colonies while avirulent form glossy colonies.
M, T, R are proteins found on outer part of cell wall and forms the basis of Griffith classification.

– M protein - Acts as virulence factor and antibody against it are protective.
– T and R protein - No relation to virulence

Streptococci (Except enterococci) are usually susceptible to penicillin so option “d” is not completely wrong. As option “a” is completely wrong, that would be the answer.