THE EFFECT OF MODIFICATIONS IN THE COUNTING MEDIUM ON THE VIABILITY AND GROWTH OF BACTERIA DAMAGED BY PHENOLS

Abstract

SUMMARY Bacteriological agar has been shown to be toxic towards Escherichia coli and Staphylococcus aureus . The effect was observed when nutrient agar was treated with Norit or ferric chloride and when the agar component alone was treated similarly. With both agents, larger colonies from untreated suspensions of Staph. aureus and higher counts from phenol treated suspensions of both species, were produced. Aluminium and chromium gave effects similar to those of iron, but iron gave the largest colonies of Staph. aureus. Magnesium also was especially successful in inducing high counts of damaged cells. A batch of Japanese agar, although apparently of poor quality, was superior by both the above criteria to two batches of New Zealand agar; but all three batches of agar were toxic to some degree.