- Tinsdale Agar is used for the primary isolation and identification of Corynebacterium diptheriae. The medium differentiates between C. diphtheriae and the diphtheroids found in the upper respiratory tract and sometimes on the skin. This differentiation was based on the ability of C. diphtheriae to produce greyish-black colonies, surrounded by a brown/black halo. Diphtheroids do not have this ability.
Corynebacterium diphtheriae on Tinsdale medium
Brown halo surround Corynebacterium diphtheriae colonies
- Tinsdale original formulated an agar containing cystine, serum, tellurite and formolised blood. Later it was modified by Billings to a medium with improved differential qualities.
- Due to the production of H2S, the potassium tellurite (present in the supplement) is reduced to a metallic tellurite and forms a dark (black to brown) halo surrounding the colony. Additionally potassium tellurite inhibits the gram negative bacteria and most of the upper respiratory tract normal flora.
- Diphtheroids (C. pseudodiphtheriticum), Haemophilus, Klebsiella, Neisseria, Staphylococcus and Streptococcus species build dark, brown colonies without halos.
