What will grow on mannitol salt agar besides staph?

Answer 1

Mannitol Salt Agar (MSA) is a selective/differential media that inhibits the growth of gram negative bacteria. Only a few bacteria can tolerate the 7.5% NaCl found within this media. The high salt content selects for Staphylococcus and a few salt tolerant enterococci. The presence of the sugar mannitol gives this media its differential properties. When mannitol is fermented (utilized by the bacteria) microorganisms release acidic byproducts that change the pH of the surrounding media. The pH change is indicated by a change in the pH indicator (phenol red) from pink to yellow.

Answer 2

Mannitol salt agar is a selective and differential primary culture medium useful in recovery and identification of staphylococci from specimens containing mixed flora. The high salt concentration (7.5%) inhibits most gram-negative and gram-positive bacteria except Staphylococcus species. Staphylococcus aureus is able to ferment mannitol, the sole carbohydrate in the medium, to produce acid products. This lowers the pH and changes the color of the pH indicator, phenol red, to yellow. Colonies of S. aureus typically appear yellow, surrounded by a yellow zone. Other Staphylococcus and Micrococcusspecies usually do not ferment mannitol and therefore produced reddish colonies that may exhibit a red to purple surrounding zone due to peptone breakdown.

Reference:

Mahon, C. Manuselis, George: Textbook of Diagnostic Microbiology 2nd Edition 2000; Selected Bacteriologic Culture Media APPENDIX A (pg. 1130)

Answer 3

Mannitol salt agar is selective for Staphylococcus species due to its high salt concentration. However, some species of Micrococcus can also grow on this medium due to their salt tolerance.