Overview:
BROLAC Agar is a differential, non-selective solid medium used primarily for the isolation and rapid differentiation of lactose-fermenting and non-fermenting Enterobacteriaceae from foods, dairy products, and environmental samples. The medium contains bromothymol blue as pH indicator and lactose as the sole fermentable carbohydrate. Lactose-fermenters produce yellow colonies, whereas non-fermenters remain blue-green.
Applications:
Rapid screening of coliforms vs. Salmonella/Shigella in food microbiology
Preliminary differentiation after selective enrichment
Teaching and routine laboratories where simple, cost-effective differentiation is needed
Traditional medium in some European food-control protocols
Key Features:
Clear colour change: yellow (lactose +) vs. blue-green (lactose �)
No inhibitors ? good growth of injured cells
Transparent base ? easy colony counting and picking
Composition (per liter):
Peptone 10.0 g
Meat Extract or Beef Extract 5.0 g
Lactose 10.0 g
NaCl 5.0 g
Bromothymol Blue 0.06�0.08 g
Agar 12.0�15.0 g
Final pH: 7.2 � 0.2 at 25�C
Preparation:
Suspend 42.1�42.3 g dehydrated medium in 1 L purified water.
Heat with frequent agitation and boil for 1 minute.
Autoclave at 121�C for 15 minutes.
Cool to 45�50�C, mix well, and pour plates.
Colony appearance (18�24 h at 35�37�C):
Lactose fermenters (E. coli, Klebsiella, Enterobacter): yellow to yellow-green colonies with yellow halo
Lactose non-fermenters (Salmonella, Shigella, Proteus): blue-green to dark blue colonies
Pseudomonas: often irregular, greenish
Storage:
Dehydrated medium: cool, dry place below 30�C
Prepared plates: 2�8�C, protected from light, use within 4 weeks
For food and general microbiology use only.
Classic medium still found in many European and Asian teaching/research labs.