Technical Advantage: Effective against Gram-positive and Gram-negative bacteria This product is a mix of the antibiotics Penicillin (10,000 IU/mL) and Streptomycin (10,000 µg/ml) in a 100-fold working concentration. Penicillin (Penicillin G) works by inhibiting peptidoglycan synthesis, while Streptomycin inhibits protein synthesis. Penicillin-Streptomycin is effective against Gram-negative and Gram-positive bacteria.