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Vocabulary flashcards covering key terms related to selective & differential media (EMB, MSA) and the streak-for-isolation technique discussed in Week 6.
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Selective Medium
A culture medium formulated to inhibit the growth of some microorganisms while allowing others to grow.
Differential Medium
A medium designed to distinguish between microorganisms, often through visible color changes produced by metabolic differences.
Eosin Methylene Blue (EMB) Agar
Selective for Gram-negative bacteria and differential for lactose fermentation; strong fermenters produce metallic green, black, or purple colonies.
Mannitol Salt Agar (MSA)
Selective for Gram-positive staphylococci due to 7.5 % NaCl and differential for mannitol fermentation indicated by a yellow color change.
Enterobacteriaceae (Enterics)
Gram-negative bacilli commonly found in the gut or soil that can ferment lactose and other sugars.
Escherichia coli (E. coli)
A lactose-fermenting enteric that forms a metallic green sheen on EMB agar.
Staphylococcus aureus
Gram-positive staphylococcus that ferments mannitol, turning MSA yellow.
Staphylococcus epidermidis
Gram-positive staphylococcus that grows on MSA but does not ferment mannitol; medium remains pink/red.
Pseudomonas aeruginosa
Gram-negative rod that grows on EMB without dark coloration because it does not ferment lactose.
Phenol Red Indicator
pH indicator in MSA that turns yellow in acidic conditions produced by mannitol fermentation.
7.5 % NaCl
High salt concentration in MSA that inhibits most bacteria except staphylococci, making the medium selective.
Streak for Isolation
Technique that dilutes bacterial samples across an agar plate to obtain discrete colonies for pure cultures.
T Streak
Three-section streak pattern shaped like a ‘T’ used to isolate colonies on an agar plate.
Quadrant Streak
Four-section streak method that progressively dilutes bacteria to achieve isolated colonies.
Metallic Green Sheen (on EMB)
Colony appearance indicating high acid production from lactose fermentation, characteristic of E. coli.