Why penicillin and streptomycin is added to culture medium?

Penicillin and streptomycin are added to culture mediums primarily to prevent bacterial contamination during the growth of desired microorganisms or cell cultures. Penicillin targets gram-positive bacteria by inhibiting cell wall synthesis, while streptomycin interferes with bacterial protein synthesis, effectively suppressing the growth of a broad range of gram-negative and some gram-positive bacteria. This combination helps ensure a sterile environment, allowing for the successful cultivation of the intended organisms without interference from contaminants.