Chapman Stone Agar Usp 1017 Condalab

Chapman Stone Agar is used for the isolation of pathogenic Staphylococci in foods. It is like Staphylococcus N° 110 Agar (Cat. CL-1032) but contains ammonium sulphate to detect the gelatinase activity (Stone’s reaction), and sodium chloride concentration is reduced to 5.5%. The main modification of this medium is the inclusion of ammonium sulphate that allows the direct observation of gelatin hydrolysis instead of adding reagents to the plate medium. Due to the presence of ammonium sulfate in the medium itself, there is no need to flood the plate with the ammonium solution to detect the gelatin liquefaction (Stone’s method). Ammonium sulphate precipitates unhydrolyzed gelatin, so a transparent halo will appear around the gelatinase (+) colonies. Casein peptone provides nitrogen, vitamins, minerals, and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. D-Mannitol is the fermentable carbohydrate providing carbon and energy. Sodium chloride, in high concentrations, inhibits most bacteria except Staphylococci.

Gelatin is a protein derived by the hydrolysis of collagen, found abundantly in bones, skin, tendons, cartilage, and animal tissue. It is used in culture media to determine gelatinolysis by bacteria. The gelatinoses produced by the microorganisms hydrolyse, the gelatin liquefying a solid medium or preventing the gelation of a medium containing gelatin. Bacteriological agar is the solidifying agent. The staphylococcal colonies are yellow, yellow-gold or orange, ferment mannitol, coagulase-positive, produce beta-haemolysis in media such as Blood Agar (Cat. CL-1108) and are gelatinase-positive. Any pigmented colony that is surrounded by a clear zone is probably a pathogenic Staphylococcus. Pale colonies, practically lacking in colour or not producing pigment, should not be considered as positives, even if they are surrounded by a clear zone (halo), and are presumptively identified as S. epidermidis colonies. It is recommended to pick the colony and inoculate it in 0,1-0,2 ml of Brain Heart Infusion Broth (Cat. CL-1400) and perform the coagulase test. At the same time, add a drop of Bromocresol purple to the colony site to determine mannitol fermentation: a yellow colour formation is a positive reaction. The zones of clear halos around the colonies indicate degradation by the enzyme gelatinase (gelatin hydrolysis).