Azide Blood Agar Base M158
Azide Blood Agar Base is used for the selective isolation and cultivation of Staphylococcus Streptococcus Streptococci ; species from mixed bacterial flora.
Ingredients Gms / Litre Peptone, special 10.000 Beef extract 3.000 Sodium chloride 5.000 Sodium azide 0.200 Agar 15.000 Final pH ( at 25°C) 7.2±0.2 **Formula adjusted, standardized to suit performance parameters
Suspend 33.2 grams in 1000 ml of distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to 45-50°C. For preparing Blood Agar plates, 5% v/v sterile defibrinated blood is added aseptically. Mix well and pour into sterile Petri plates. Warning : Sodium azide has a tendency to form explosive metal azides with plumbing materials. It is advisable to use enough water to flush off the disposables.
Principle And Interpretation
Azide Blood Agar Base is recommended for the isolation and cultivation of Streptococcus species from clinical and nonclinical specimens. It is a modification of the broth medium originally formulated by Edwards for the detection of Streptococci from bovine mastitis cases (1). The original broth medium of Edwards was modified to a blood agar by Packer containing sodium azide and crystal violet (2). Peptone special and beef extract are the sources of carbon, nitrogen and essential growth factors. Sodium azide acts as a selective agent by suppressing the growth of gram-negative bacteria. It also prevents the swarming of Proteus (3, 4). Sodium chloride helps to maintain the osmotic balance of the medium. The media can be supplemented with sterile defibrinated blood to prepare blood agar. Blood serves as an additional source of growth factors and it also helps to visualize the haemolytic pattern. The pH of the medium influences the inhibitory action of sodium azide (2). At pH 7.2, sodium azide does not interfere with the haemolytic reactions of however, haemolytic pattern of Streptococci is different on Azide Blood Agar as compared on nonselective blood agar. For best results, use light inoculum and incubate anaerobically for enhancement in haemolytic reaction. Different types of haemolysis can be visualized on blood agar plates (5). The degree of haemolysis or the haemolytic pattern obtained differs with the type of blood used for preparation of blood agar, and also the composition of blood agar used (6).
Storage and Shelf Life
Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label.
1. Edwards, 1933, J. Comp. Pathol. Therap., 46:211. 2. Packer, 1943, J. Bacteriol., 1943, 46:343 3. Snyder and Lichstein, 1940, J. Infect. Dis., 67:113. 4. Lichstein and Snyder, 1941, J. Bacteriol., 42:653. 5. Isenberg, (Ed.), 1992, Clinical Microbiology Procedures Handbook, Vol. I., American Society for Microbiology, Washington, D.C. 6. Murray P. R., Baron E. J., Jorgensen J. H., Pfaller M. A., Yolken R. H., (Eds.),8th Ed., 2003, Manual of Clinical Microbiology, ASM, Washington, D.C.