Jump to content

Mannitol salt agar

From Wikipedia, the free encyclopedia
(Redirected from Mannitol Salt Agar)
An MSA plate with Micrococcus sp. (1), Staphylococcus epidermidis (2) and S. aureus colonies (3).

Mannitol salt agar or MSA is a commonly used selective and differential growth medium in microbiology. It encourages the growth of a group of certain bacteria while inhibiting the growth of others.[1] It contains a high concentration (about 7.5–10%) of salt (NaCl) which is inhibitory to most bacteria - making MSA selective against most Gram-negative and selective for some Gram-positive bacteria (Staphylococcus, Enterococcus and Micrococcaceae) that tolerate high salt concentrations.[2] It is also a differential medium for mannitol-fermenting staphylococci, containing the sugar alcohol mannitol and the indicator phenol red, a pH indicator for detecting acid produced by mannitol-fermenting staphylococci.[3] Staphylococcus aureus produces yellow colonies with yellow zones, whereas other coagulase-negative staphylococci produce small pink or red colonies with no colour change to the medium.[4] If an organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red in the agar to turn yellow.[1] It is used for the selective isolation of presumptive pathogenic (pp) Staphylococcus species.[5]

Expected results

[edit]
  • Gram + Staphylococcus: fermenting mannitol: medium turns yellow (e.g. S. aureus)
  • Gram + Staphylococcus: not fermenting mannitol, medium does not change color (e.g. S. epidermidis)
  • Gram + Streptococcus: inhibited growth
  • Gram -: inhibited growth[1]

Typical composition

[edit]

MSA typically contains:[6]

References

[edit]
  1. ^ a b c Bachoon, Dave S.; Dustman, Wendy A. (2008). "Exercise 8: Selective and Differential Media for Isolation". In Michael Stranz (ed.). Microbiology Laboratory Manual. Mason, OH: Cengage Learning.
  2. ^ "Mannitol salt agar" (PDF). Becton, Dickinson and Company. 2005. Archived from the original (PDF) on 2009-01-26.
  3. ^ Anderson, Cindy (2013). Great Adventures in the Microbiology Laboratory. Pearson. pp. 175–176. ISBN 978-1-269-39068-2.
  4. ^ "Mannitol salt agar (7143)" (PDF). Neogen Corp. 2011. Archived from the original (PDF) on 2016-03-03.
  5. ^ Identification of Staphylococcus aureus: DNase and Mannitol salt agar improve the efficiency of the tube coagulase test
  6. ^ The United States Pharmacopeia (23rd ed.). Rockville, MD: The United States Pharmacopeial Convention. 1995.