Antibiotic-Antimycotic is a solution that is commonly added to cell culture media to prevent contamination by various bacteria and fungi. It generally contains 10,000 units per milliliter penicillin, 10,000 micrograms per milliliter streptomycin, and 25 micrograms per milliliter amphotericin B.[1]

Penicillin is a Beta-lactam antibiotic that is effective in inhibiting Gram-positive bacteria. Streptomycin is an aminoglycoside antibiotic which is effective against most Gram-negative bacteria. Amphotericin B is effective against multi-cellular fungi and yeasts.
https://en.wikipedia.org/wiki/Antibiotic-Antimycotic