Thermo Scientific™ Iso-Sensitest Agar (Dehydrated)

Description

Perform effortless antimicrobial susceptibility testing using Thermo Scientific™ Oxoid™ Iso-Sensitest Agar (Dehydrated), a semi-defined medium specifically designed for antimicrobial susceptibility testing (AST). Iso-Sensitest Broth is carefully constructed to give reproducible results. It allows the growth of the majority of microorganisms without the need for further supplementation.

Iso-Sensitest Agar has been designed to overcome objections made about Mueller-Hinton Media by various workers ^{1,2,3,4,5,6,7}

These objections were:

1. Different MIC values in the broth and agar versions of the medium.
2. Agar versions showing antagonistic effects towards tetracycline.
3. High levels of sulphonamide and trimethoprim antagonists.
4. Poor reproducibility with different manufacturers' peptones.
5. Poor growth-supporting ability for streptococci and variable growth rates with gram-positive organisms generally

Some mutant strains which are totally dependent on thymine and thymidine for their growth will, however, not grow in Iso-Sensitest Agar, which has these two compounds at very low levels, as they are the naturally occurring antagonists of trimethoprim. Care must be taken to recognize these strains^8,9,10.

Iso-Sensitest Agar was developed from Oxoid™ Sensitest Agar (CM0409) which has been used successfully in several centers throughout the world^11,12,13. The role of metal ions as antagonists to certain antibiotics has been described by many workers^{14,15,16,17,18,19}. A stabilized mineral content in sensitivity test media is, therefore, important.

Reller, Schoenknecht, Kenny & Sherris³ demonstrated the contribution of cations provided in media by ordinary agars. A considerable difference in mineral content between the agar and broth media was shown. Only by using an agar which is specially processed to remove the free anions and cations can a stabilized mineral content be obtained.

Iso-Sensitest Agar has stability in mineral content and the ability to produce optimum antimicrobial zones of inhibition. The amino-nitrogen base of acid-hydrolyzed casein and special peptones has been supplemented with defined growth factors. Careful preparation of the nutrients ensures that trimethoprim and sulphonamide antagonists are at very low levels.

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Remel™ and Oxoid™ products are now part of the Thermo Scientific brand.