BROLAC Agar (Bromothymol-blue Lactose Agar)

EMD Cat. No. 1.01639.0500
500 g


Elective culture medium, free from inhibitors, for separating lactose-positive from lactose-negative colonies, used especially for Enterobacteriaceae.

Typical Composition (g/liter)                               


Mode of Action
 BROLAC agar contains lactose which, when degraded to acid, causes the pH indicator bromothymol blue to change its color to yellow. Alkalinization produces a blue coloration.

Typical Composition (g/liter)
 Peptone from meat 3.5; peptone from casein 3.5; sodium chloride 5.0; lactose 15.5; bromothymol blue 0.04; agar-agar 13.0.

Preparation
 Suspend 40.5 g in 1 liter of purified water. Autoclave (15 min at 121°C), pour plates.
 pH: 7.0 ± 0.2 at 25°C.
 The plates are clear and green to green-blue.

Experimental Procedure and Evaluation
 Inoculate by thinly speading the sample material on the surface of the plates.
 Incubation: 24 hours at optimum temperature, usually 35 °C aerobically.

Appearance of Colonies
 		Microorganisms
Green to blue, sometimes surrounded by a blue zone
 		Lactose-negative:
 Salmonella, Shigella, Serratia, Proteus, Providencia and others.
Golden yellow, surrounded by a yellow zone
 		Lactose-positive:
 Escherichia, Coliform bacteria and others.


Quality control
Test strains
 Growth
 		color change to yellow
Escherichia coli ATCC 25922
 		good / very good
 		+
Klebsiella pneumoniae ATCC 13883
 		good / very good
 		+
Salmonella typhimurium ATCC 14028
 		good / very good
 		-
Proteus vulgaris ATCC 13315
 		good / very good
 		+ / -
Staphylococcus aureus ATCC 25923
 		fair / good
 		+ / -
Enterococcus faecalis 33186
 		fair / good
 		+