Penicillin G is a narrow spectrum antibiotic. It is the drug of choice for Streptococcus pneumoniae, groups A, B, C and G streptococci, nonenterococcal group D streptococci, viridans group streptococci, and non-penicillinase producing staphylococcus. Penicillin G potassium salt is used to study murosomes of staphylococci and the penicillin-induced lysis of Streptococcus mutans.