503 UI MEDIUM
Use Medium No. 284 supplemented with final 0.2 g yeast extract and 1.0 ml Trace vitamins solution in Solution A (per 900 ml) and with 0.414 g 4-hydroxybenzoic acid in Solution B (per 100 ml) instead of sodium pyruvate. Otherwise, prepare the medium as described in the recipe of Medium No. 284.