Magnesium and iron addition to casein hydrolysate medium for production of staphylococcal enterotoxins A, B, and C

From comparisons of 4% N-Z Amine NAK made with distilled water, naturally hard water, and synthetic salt solutions, it appeared that magnesium and, to a lesser extent, iron were limiting factors in the production of staphylococcal enterotoxins B and C but not A. Maximum enterotoxin production with NAK medium was achieved by the addition of 5 mg of Mg2/ per liter (for a total of 9 mg of Mg2+ per liter) and 0.5 mg of Fe2+ per liter. Higher levels of magnesium were not inhibitory. Supplementing NAK with commonly used complex components, which added Mg2+ above the 9-mg/liter level, did not result in maximum yields of enterotoxin. Variability in the ability of different lots of NAK to support enterotoxin production may be minimized by supplementing NAK medium with magnesium and iron.