AZIDE BLOOD AGAR BASE
A medium base and ready to use plates for the isolation of Streptococci and Staphylococci.
Code: CB1/3002
Typical formula g/l
| Tryptose |
10.0 |
| Beef extract |
3.0 |
| Sodium chloride |
5.0 |
| Sodium azide |
0.2 |
| Agar |
15.0 |
Final pH 7.2 +/-0.2
Directions
Suspend 33.2 g in 1000 ml of cold distilled water. Heat to boiling and sterilise by autoclaving at 121°C for 15 minutes. Cool to 50°C and, under aseptic conditions; add 5% sterile defibrinated blood.
WARNING: Read Hazardous precautions for media containing azide.
Description
Azide Blood Agar Base is recommended for the selective isolation of streptococci and staphylococci from faeces, water, foodstuffs and other specimens grossly contaminated with Gram-negative flora. The review by Hartman et al. lists more than forty types of selective media for streptococci with sodium azide base; this substance has a bacteriostatic effect on a number of bacterial species, particularly Gram-negative ones (probably by blocking the metalloporphyrinic enzymatic systems: catalase, cytochrome C oxidase). It inhibits the swarming of Proteus spp., which does not interfere with the phenomenon of haemolysis, and allows the development of some Gram-positive species, particularly streptococci, staphylococci and some anaerobes. The material under examination can be plated onto the surface, or included into the agar mass. The latter method is preferable: it is noticed that streptolysin O is inactivated by oxygen and that some strains of streptococci grow better when oxygen presence is reduced. Several authors recommend anaerobic incubation, or the preparation of a double set of plates, one for anaerobic and the other for aerobic incubation. The typical appearance of haemolysis in Azide Blood Agar plates is as follows: α-haemolysis: greenish-brown ring, sometimes surrounded by a light zone; under the microscope the red cells appear discoloured but intact. β-haemolysis: transparent red ring. The diagnosis of streptococci is confirmed with standard microscopic, biochemical and serological examination.
User quality assurance (37°C-24 h)
Productivity control
S.pyogenes ATCC 19615: growth, beta haemolysis
S.pneumoniae ATCC 6305: growth alpha haemolysis
S.aureus ATCC 25923: growth
Selectivity control
P.mirabilis ATCC 12453: partially inhibited
Storage
Dehydrated medium: 15-30°C
User prepared plates: up to 7 days at 2-8°C
References
Hartman. P.A. Beinbold, G.W. & Saraswat D.S. (1966) - Adv. Appl. Micr. 8, 253-289.
Moody, M.D. (1972) - Old and new techniques for rapid identification of Group A Streptococci.
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