LB6-4-3 Mannitol Salt Agar
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9 terms
Terms | Definitions |
|---|---|
 3 Broth Cultures | Escherichia Coli Staphylococcus Epidermidis Staphylococcus Aureus |
| Mannitol salt is both: | Selective media & Differential media |
| Selective Media | Favors growth of Staphylococcus species Inhibits growth of Gram (-) bacteria |
| Differential Media | Isolate Staphylococcus aureus from other staph species |
| MSA Contains: | 1.NaCl-7.5%-inhibits Gram (-) bacteria (E. Coli) 2.Mannitol-carbohydrate S. aurerus produces enzyme-mannitol dehydrogenase-breaks mannitol into pyruvate which ferments to produce an acid 3. Phenol Red-pH indicator Yellow (acid) < 6.8 Red (neutral) 7.4-8.4 Pink (base) > 8.4 |
| 1. What purpose does the Nutrient Agar plate serve? In what way does it increase validity of the test result? | Serves as a control Increases validity-shows that Gram (-) bacteria (e. coli) are viable |
| What would be the likely consequence of omitting the NaCl in Mannitol Salt Agar? Why? | Salt is the selective ingredient. With no NaCl, all organisms, Gram (+) & Gram (-) would grow equally |
| With the diversity of microorganisms in the world, how can a single test such as MSA be used to confidently identify staphylococcus aures? | Salt levels in MSA inhibit all Gram (-) leaving gram (+) cells. Only staph species can tolerate high salt, eliminating all other gram (+) microbes Only S. Aures can ferminent mannitol, eliminating all other staph species. |
| RESULTS: | E. Coli-no growth! Why? 7.5% salt inhibition S. Aureus-Yellow!-Enzyme breakdown Mannitol-produce acid S. Epidermidis S. Aures fermits mannitol acid (yellow) S. Epidermidis grows but cant fermit mannitol-no acid E. Coli-No growth-high salt |
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