Tellurite Blood Agar I Purpose and Composition I Selective Media I Bacterial Culture Media I Microbe скачать в хорошем качестве

Tellurite Blood Agar I Purpose and Composition I Selective Media I Bacterial Culture Media I Microbe

Tellurite Blood Agar (TBA) is a selective medium containing potassium tellurite and blood, mainly used for the isolation of Corynebacterium diphtheriae. Colonies appear black or gray due to tellurite reduction, which helps in selective identification. Tellurite Blood Agar (TBA) is a selective and differential medium used primarily for the isolation of Corynebacterium diphtheriae (the causative agent of diphtheria). It is a blood agar base supplemented with potassium tellurite, which inhibits most respiratory flora while allowing C. diphtheriae to grow. 2. Purpose / Uses Selective isolation of Corynebacterium diphtheriae from throat swabs, nasal swabs, and clinical specimens. Differentiates Corynebacterium based on tellurite reduction → colonies turn gray to black. Used in diagnostic microbiology for diphtheria detection. 3. Composition (per liter, typical) Base: Blood Agar / Infusion Agar Peptone – 10 g (amino acids, nitrogen source). Beef extract – 5 g (growth factors, vitamins). Sodium chloride – 5 g (osmotic balance). Agar – 15 g (solidifying agent). Defibrinated sheep blood – 50 mL (enrichment). Potassium tellurite (0.04%) – selective agent (inhibits most flora, reduced to metallic tellurium → black colonies). Final pH: 7.4 ± 0.2 at 25 °C 4. Principle Tellurite → inhibits most Gram-negative bacilli and many Gram-positive organisms. Corynebacterium diphtheriae reduces tellurite → metallic tellurium, giving black/gray colonies. Blood in the medium enhances growth of fastidious organisms and allows observation of hemolysis patterns. 5. Colony Characteristics Corynebacterium diphtheriae: Gray to black colonies due to tellurite reduction. May show halo zones around colonies. Other throat flora: Mostly inhibited. 6. Summary Tellurite Blood Agar (Selective Media): Purpose: Selective medium for isolation of Corynebacterium diphtheriae (diphtheria). Composition: Peptone, beef extract, NaCl, agar, sheep blood, potassium tellurite. Key Point: C. diphtheriae → gray/black colonies from tellurite reduction.