Mannitol Salt Agar with Oxacillin (4μg/mL)

Selectively and differentially isolate methicillin-resistant staphylococci from clinical specimens using Thermo Scientific™ Remel™ Mannitol Salt Agar with Oxacillin (4μg/mL). This agar contains 7.5% sodium chloride as a selective agent as reported by Koch in 1942¹. Coagulase-positive staphylococci strains grow on this agar, producing yellow zones because of mannitol fermentation whereas coagulase-negative staphylococci strains produce tiny colonies with no color change.

Staphylococci are widespread in nature, although they are mainly found on the skin, skin glands and mucous membranes of mammals and birds. The coagulase-positive species, i.e. Staphylococcus aureus, is well documented as a human opportunistic pathogen. The ability to clot plasma continues to be the most widely used and accepted criterion for the identification of pathogenic staphylococci associated with acute infections². One of the pathogenic strains is methicillin-resistant strain. Methicillin resistance is associated with production of a unique penicillin-binding protein (PBP), 2a, which is bound and inactivated only at high concentrations of beta-lactam antibiotics. The heterogeneous expression of methicillin resistance by staphylococci poses problems in the detection of resistant strains³.

Use Mannitol Salt Agar with Oxacillin for selective and differential isolation of methicillin-resistant staphylococci.

• Easy-to-differentiate: Differentiates between coagulase-positive and coagulase-negative staphylococci.
• Selective: Sodium chloride in the concentration of 7.5% inhibits many bacteria other than staphylococci.
• Ready-to-use: Convenience of prepared media.

This medium contains casein and meat peptones that supply nitrogen, amino acids, and peptides necessary for bacterial growth. Beef extract is a source of essential nutrients, carbon and sulfur for microbial growth. Phenol red is the pH indicator which causes a color change in the medium from red-orange to yellow when acid is produced. Colonies of Staphylococci that ferment mannitol will be surrounded by a yellow zone, while those that do not ferment mannitol will have no color change. Oxacillin (4μg/ml) is added to inhibit the growth of non-MRSA staphylococci and other susceptible organisms.

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