Bile Esculin Azide (BSA) Medium

Bile Esculin Azide (BSA) medium is a differential medium in the isolation and presumptive identification of enterococci/group D streptococci. Esculin hydrolysis was first described by Rochaix in 19241 and Swan introduced the use of Bile Esculin Agar in 19542. The ability to hydrolyze esculin in the presence of bile is a characteristic of enterococci and group D streptococci. According to Facklam and Moody the bile esculin test provided a reliable means of identifying group D streptococci and differentiating them from non-group D streptococci3. Other researchers have used this medium for the presumptive identification of Enterobacter spp., Klebsiella spp., and Serratia spp., among the Enterobacteriaceae.

Enterococci and certain streptococci hydrolyze esculin, to esculetin and dextrose. Esculetin then reacts with Ferric citrate forming a dark brown or black iron complex from its original amber color. This color formation is an indicator of esculin hydrolysis. Oxgall and Sodium azide are added to the medium for additional selectivity where it inhibits growth of gram-positive bacteria. Vancomycin can be added BSA medium to identify and isolate vancomycin resistant enterococci and group D streptococci.


Product NameCatalog #Quantity
BSA Agar mono plate, 90 x 15 mm CB9140P 10/pk
BSA Agar Slant CB9140S 10/pk
BSA Agar w/Vancomycin mono plate, 90 x 15 mm CB9141P 10/pk
BSA Agar w/Vancomycin mono plate, 90 x 15 mm w/o Glutamine & Sodium bicarbonate CB9142P 10/pk
BSA Agar Slant, w/Vancomycin CB9141S 10/pk


Quality Control



The following organisms are routinely used for testing for this medium.
Test OrganismsResults
Enterococcus faecalisb ATCC® 29212 Growth; (+)
Escherichia coli ATCC® 25922 Partial inhibition; small colorless colonies. Growth inhibited in broth.
Streptococcus pyogenes ATCC® 19615 Partial to complete inhibition; (-)


User Quality Control



Check for signs of contamination and deterioration. Users of commercially prepared media may be required to perform quality control testing with at least one known organism to demonstrate growth or a positive reaction; and at least one organism to demonstrate inhibition or a negative reaction (where applicable).

Ingredients g/L

(Final pH 7.1 +/- 0.3 at 25°C)
Pancreatic Digest of Casein 16.0
Oxbile 10.0
Yeast Enriched Meat Peptone 9.5
Sodium Chloride 5.0
Sodium Citrate 1.0
Esculin 1.0
Ferric Ammonium Citrate 0.5
Sodium Azide 0.25
Agar (where applicable) 15.0
3 total citations

  1. Rochaix. 1924. Cr. Soc. Biol., Paris; 90:771.
  2. Swan, A. 1954. J. Clin. Path.; 7:160-163.
  3. Facklam, R.R., and M.D. Moody. 1970. Appl. Microbiol., 20:245
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