Effect of secondary metabolites on the organisms producing them: effect of nisin on Streptococcus lactis and enterotoxin B on Staphylococcus aureus.

The effect of secondary metabolites added to cultures of the organisms producing them was investigated. Nisin was added to growing cultures of a nisin-producing strain of Streptococcus lactis (354/07) and enterotoxin B to strains of Staphylococcus aureus (S6 and 243) producing enterotoxin B. One quarter (12 mug/ml) of the amount of nisin formed by the culture of S. lactis inhibited lag-phase cells and lysed log-phase cells. The same amount of nisin added before inoculation or at a time when nisin synthesis had started (in late log phase), caused only transient delay in growth. Inhibition of growth of the two enterotoxin B-producing strains of S. aureus could not be demonstrated at any stage of their growth cycle with as much as 1 mg of enterotoxin B per ml of medium.