Selective & Differential Media: Gram Negative Bacteria

These flashcards cover key vocabulary related to selective and differential media used for isolating and identifying Gram-negative bacteria.

MacConkey (MAC) Agar

A selective and differential medium that isolates and differentiates Enterobacteriaceae based on lactose fermentation.

Selective Medium

A type of media that inhibits the growth of certain bacteria while allowing others to grow.

Differential Medium

A type of media that allows differentiation of bacteria based on their biochemical activities.

Enterobacteriaceae

A family of bacteria that includes both coliforms and non-coliforms, often associated with intestinal flora.

Lactose Fermentation

The metabolic process by which bacteria convert lactose into lactic acid; often indicated by a color change on culture media.

Neutral Red Dye

A pH indicator used in MacConkey agar that turns pink in acidic environments (pH < 6.8) and colorless in neutral or basic environments.

Coliform Bacteria

Bacteria that are indicators of fecal contamination; capable of fermenting lactose.

Eosin Methylene Blue (EMB) Agar

A selective and differential medium for Gram-negative bacteria that detects lactose fermentation.

Green Metallic Sheen

Characteristic appearance on EMB agar indicating strong acid production from lactose fermentation, seen in E. coli.

Hektoen (HEK) Enteric Agar

A complex medium used to isolate Salmonella and Shigella from other enteric bacteria, useful in identifying sulfur reducers.

Hydrogen Sulfide (H2S) Production

A metabolic process in which bacteria reduce sodium thiosulfate to produce hydrogen sulfide gas, indicated by black colonies.

Coliform vs Noncoliform

Coliforms produce acid from lactose fermentation resulting in yellow or salmon colonies, while noncoliforms do not.