AESCULIN BILE AZIDE  BROTH

 

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Selective liquid medium with sodium azide for the isolation and differentiation of Group D Streptococci.

 

Code: CB1/3142

 

Typical formula g/l

 

Tryptone	17.00
Peptone	3.00
Yeast extract	5.00
Oxgall	10.00
Sodium chloride	5.00
Sodium citrate	1.00
Aesculin	1.00
Ferric ammonium citrate	0.50
Sodium azide	0.25

 

Final pH 7.1 +/- 0.1

 

Directions

Suspend 55.7g of agar or 42.7g of broth in 1000 ml of cold distilled water. Heat to boiling with frequent agitation the agar medium or heat to dissolve the liquid medium. Distribute and sterilise by autoclaving at 121°C for 15 minutes. Do not exceed sterilisation time and tem­perature.

 

 

Description

Aesculin Bile Azide Agar and Aesculin Bile Azide Broth are selective and diagnostic media for the detection of group D Streptococci. These microorganisms grow in the presence of sodium azide and bile salts and are additionally capable of hydrolysing aesculin to glucose and aglycone 6-7 dihydroxycumarin: The aglycone reacts with the iron salts in the medium, giving them a black colouring.  Aesculin Bile Azide Agar can be used with 8 mcg/ml of vancomycin for the screening of  Vancomycin Resistant Enterococci.

 

In use

Prepare tenfold dilutions of the sample with peptone water. Within 3 hours from the sample preparation, spread 0.1 ml of the inoculum onto the plates. Incubate at 35°C or at 42°C for 18-24 hours (the higher incubation temperature increases the selectivity of the medium). Colonies of enterococci on Aesculin Bile Azide Agar (after 24 hours of incubation at 37^°C) have the following characteristic appearance: Convex colonies, translucent or whi­tish, 1-2 mm diameter, dark brown or black surrounding zone; in­cubation should not be prolonged beyond 24 hours, because ex­tensive blackening of the medium makes reading difficult. 

 

Using a sterile inoculating loop, inoculate broth with well-isolated colonies. Incubate at 37°C for 18-24 hours and observe for growth and blackening.

 

 

User quality assurance (37°C-24 and 48 h)  

 

Productivity control

E.faecalis ATCC 29212*:

Aesculin Bile Azide Agar : good growth with blackening of medium around the colonies

Aesculin Bile Azide Broth: the liquid medium turns black

 

Selectivity control

S.pyogenes ATCC 19615*: partially inhibited

E.coli ATCC 25922*: inhibited

*NCCLS M22-A2 recommended strains.

 

Storage

Dehydrated media: 15-30°C

User prepared plates: up to 7 days at 2-8°C

User prepared tubes and flasks: 1 month at 2-8°C

 

References  

Isenberg, H.D., Goldberg, D. & Sampson, J. (1970) Appl. Micr., 20, 433-436.

Jensen Bette, J. (1996) Lab.Med. 27, 53

NCCLS document M22-A2, 1996. Quality Assurance for Commercially prepared Microbiological Culture Media-2^nd ed.; Approved Standard.

Swan, A. (1954) J. Clin. Path, 7, 160-163.

Williams, R.E.O. & Hirch, A. (1950). J. Hyg (Camb.), 48, 504