The antibiotics penicillin and streptomycin have potent combined antibacterial effects against Gram-positive and Gram-negative bacteria and can be used to prevent bacterial contamination of cell cultures.Penicillin, originally purified from the fungus Penicillium, works by directly interfering with bacterial cell wall turnover and indirectly by triggering the release of enzymes that can further alter the cell wall.Streptomycin was originally purified from Streptomyces griseus.Its mechanism of action is to bind to the 30S subunit of bacterial ribosomes, thereby inhibiting protein synthesis and causing the death of sensitive bacteria.The solution contains 10,000 units of penicillin, 10,000 μg of streptomycin, and 29.2 mg/mL of L-glutamine in 10 mM citrate buffer (to maintain pH stable).