Hemolytic colonies with gram-positive cocci in chains suggest either alpha or beta-hemolytic streptococci. Bacitracin sensitivity is used to differentiate between streptococci as follows: Group A: Bacitracin sensitive Group B: Bacitracin resistant Bile solubility and optochin sensitivity are used to differentiate Pneumococcus and Streptococcus viridans Catalase test is used to differentiate Streptococcus and Staphylococcus Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition