drops of a 0.04% bromothymol-blue solution are applied to colony sites; the individual colonies should first be removed with a platinum loop.
According to STONE (1935), gelatinolysis is an indicator of toxicity and it is shown by the appearance of clear zones around the colonies about 10 minutes after applying drops of a saturated ammonium sulfate solution or a 20% sulfosalicylic acid solution.
Further tests should be performed to confirm the results.