Trypticasein Soy Agar (TSA) No.2

Trypticasein Soy Agar No. 2, supplemented with 5% sheep blood, offers clear and visible hemolytic reactions with group A streptococci (Streptococcus pyogenes).

Tryptone H enhances hemolysin production. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Soy peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Bacteriological agar is the solidifying agent. Blood is an additional source that provides growth factors for the microorganisms and is the basis for determining haemolytic reactions.

Hemolytic streptococci can be seen as translucent or opaque, grayish, small (1 mm), or large matt and mucoid (2-4 mm) colonies, surrounded by a hemolysis zone. Staphylococci appear as opaque, white to gold-yellow colonies with or without zones of beta hemolysis.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 40 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation and boil for one minute. Sterilize in autoclave at 121 °C for 15 minutes. Cool to 45-50 °C, and add 5-10% sterile defibrinated blood, homogenize and pour into Petri dishes. Be careful to avoid bubble formation when adding the blood to the cooled medium and rotate the flask or bottle slowly to create a homogeneous solution.

Instructions for use

Inoculate and incubate the plates at a temperature of 35 ± 2 °C in an atmosphere with 5-10% CO₂ and observe after 18-24 hours.

• U.S. Food and Drug Administration. 1995. Bacteriological analytical manual, 8th ed. AOAC International, Gaithersburg, Md.
• Downes and Ito (ed.). 2001. Compendium of methods for the microbiological examination of foods, 4th ed. American Public Health Association, Washington, D.C.
• Ruoff, Whiley and Beighton. 1999. In Murray, Baron, Pfaller, Tenover and Yolken (ed.), Manual of clinical microbiology, 7th ed. American Society for Microbiology, Washington, D.C.