Selective vs. Differential Media

What is differential media?

Differentiates closely related organisms or groups of organisms based on the organism's biochemical characteristics.

What organisms show an A/A TSI?

E. coli, Klebsiella pneumoniae, Enterobacter aerogenes

What organisms are lactose fermenters?

E. coli, Klebsiella pneumoniae, enterobacter aerogenes.

What organisms are positive for H2S?

Salmonella

What bacteria show K/A TSI?

Salmonella enteritidis, Citrobacter diversus, Proteus mirabilis, Morganella morganii, Providencia alcafaciens

What organisms are not lactose fermenters?

Salmonella enteritidis, Citrobacter diversus, Proteus mirabilis, Morganella morganii, Providencia alcafaciens, Alcaligenes faecalis, Pseudomonas aeruginosa

For what is MacConkey Agar selective and differential?

Selective: for Gram-negative bacteria because bile salts and crystal violet inhibit the growth of Gram-positive bacteria. Differential: based on ability to ferment lactose (bacteria that can ferment lactose cause a drop in pH which turns indicator pink).

For what is mannitol salt agar selective and differential?

Selective: high salt selects for Staphylococci. Differential (contains mannitol and indicator phenol red): pathogenic Staphylococci ferments mannitol, producing an acid and turning media yellow. Non-pathogenic Staphylococci do not ferment mannitol and so leave the media pink.

What is a triple sugar iron test?

Tests for sugar fermentation and sulfur reduction. Glucose is limiting but lactose and sucrose are abundant. Rapid glucose fermentation decreases pH in butt (red slant and yellow butt). Fermentation of glucose and actors &/or sucrose results in yellow slant and butt. Sulfur reducers produce H2S, resulting in a black precipitate. CO2 production yields cracks in agar. Acid (A)=yellow. Alkaline (K)=red.

What bacteria show K/K TSI?

Alcaligenes faecalis, Pseudomonas aeruginosa

What is selective media?

Allows the growth of some organisms while inhibiting the growth of others.