Overview:
Bile Esculin Azide Agar is a highly selective and differential solid medium specifically designed for the isolation and presumptive identification of enterococci (Enterococcus faecalis, E. faecium, E. durans, E. avium, etc.) from clinical, food, water, and environmental samples. It combines three selective agents (bile, sodium azide, and high salt) with the esculin�ferric citrate system. Only enterococci grow well and produce characteristic black halos within 24�48 h. It is the reference medium in ISO 7899-2 (water) and many food microbiology standards.
Applications:
Isolation and enumeration of enterococci in drinking, bathing, and waste water (ISO 7899-2)
Detection of faecal enterococci in foods, dairy, and meat products
Confirmation of enterococci in clinical specimens (especially VRE screening)
Preferred over BEA when maximum selectivity is required
Key Features:
Triple selection: 0.04 % bile + 0.015 % sodium azide + high salt ? inhibits streptococci, staphylococci, Gram-negatives
Esculin hydrolysis ? intense black zones around colonies
Faster and cleaner results than Bile Esculin Agar alone
Positive reaction visible in 18�24 h
Composition (per liter):
Peptone 17.0 g
Beef Extract 3.0 g
Yeast Extract 5.0 g
Oxgall (bile) 10.0 g
Esculin 1.0 g
Ferric Ammonium Citrate 0.5 g
Sodium Chloride 5.0 g
Sodium Azide 0.15 g
Agar 15.0 g
Final pH: 7.1 � 0.2 at 25�C
Preparation:
Suspend 56.65 g dehydrated medium in 1 L purified water.
Heat with frequent agitation and boil for 1 minute.
DO NOT AUTOCLAVE (azide and esculin are heat-sensitive).
Cool to 45�50�C, swirl gently, and pour plates.
Incubation:
35�37�C for 24�48 h (most enterococci positive within 24 h).
Interpretation:
Enterococci: black or dark-brown colonies with black halo ? 5 mm
Other organisms: inhibited or growth without blackening
Storage:
Dehydrated medium: cool, dry place below 30�C
Prepared plates: 2�8�C, protected from light, use within 3 weeks
Safety note: Contains sodium azide � toxic and explosive with metals. Dispose properly.
For laboratory use only. Official reference medium: ISO 7899-2, APHA, FDA-BAM.