Mannitol Salt Agar (MSA) Quiz

Mannitol Salt Agar (MSA)

• The main selective ingredient in Mannitol Salt Agar (MSA) is a high concentration of salt (7.5-10% NaCl).
• The high salinity of MSA promotes the growth of halophilic microorganisms, besides Staphylococci, such as certain species of Micrococcus and Bacillus.
• MSA differentiates between microorganisms based on their ability to ferment mannitol, which is a sugar, and their tolerance to high salt concentrations.
• Mannitol fermentation is indicated by a yellow color change in the agar, while non-fermenters produce a pink or red color.

Staphylococcus aureus

• The strain of Staphylococcus aureus often implicated in infections obtained in hospital settings is Methicillin-Resistant Staphylococcus aureus (MRSA).
• Staphylococcus aureus can acquire resistance to antibiotics through horizontal gene transfer, mutation, and gene expression.
• Resistance to antibiotics can be acquired through the production of enzymes that degrade antibiotics, alteration of target sites, and active efflux of antibiotics.

Detection of Antibiotic-Resistant Strains

• Detection of MRSA or other antibiotic-resistant strains can be performed using Mannitol Salt Agar, which selects for Staphylococci and allows for the detection of mannitol fermentation.
• After isolating Staphylococci spp. on MSA, a Kirby-Bauer disk diffusion test is typically performed to determine antibiotic susceptibility.

Test your knowledge on Mannitol Salt Agar (MSA), a selective and differential media used for the identification of Staphylococcus species. Learn about the main selective ingredient, its purpose, and how it differentiates microorganisms based on their ability to ferment mannitol.