Hoyle's agar is a selective medium that uses tellurite to differentially select ''

Corynebacterium diphtheriae ''Corynebacterium diphtheriae'' is a Gram-positive pathogenic bacterium that causes diphtheria. It is also known as the Klebs–Löffler bacillus because it was discovered in 1884 by German bacteriologists Edwin Klebs (1834–1912) and Friedrich ...

'' from other

upper respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respiratory ...

flora. The medium appears cream to yellow colored, and takes the form of a free-floating powder. It is a modification of Neill's medium. Hoyle's tellurite agar contains: The medium inhibits growth of

Gram-negative bacteria Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelo ...

and many

Gram-positive bacteria In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain ...

, and reduction of the tellurite is characteristic of corynebacteria (though not entirely exclusive to them.) Microscopic examination of samples of suspected colonies, using Neisser differential

staining Staining is a technique used to enhance contrast in samples, generally at the Microscope, microscopic level. Stains and dyes are frequently used in histology (microscopic study of biological tissue (biology), tissues), in cytology (microscopic ...

, is required for confirmation.

References

Microbiological media {{Microbiology-stub