To confirm the presence
of phase I in strain 1173, which exhibits a significantly
higher level of antibiotic activity than phase II, the stock
inoculum was spread on NBTA medium (45 g nutrient
agar; 0. 025 g bromothymol blue; 0. 04 g 2,3,5-triphenyl-
tetrazolium; 1,000 mL H
2
O) and incubated at 28
±
1
°
C
for 48 h.