VP Test

One of the IMViC tests to distinguish members of Enterobacteriaceae

 alpha-napthol and KOH added to tube

Positive: Red color. 2,3-butanediol is produced through fermentation from acetoin

Negative: No color change. 2,3-butanediol is produced through fermentation with no acetoin

MR test (Methyl Red)

One of the IMViC tests to distinguish members of Enterobacteriaceae

Methyl Red is added to inoculated tube

Positive: Red color. Mixed acid fermentation takes place.

Negative: No color change. No mixed acid fermentation. 

Citrate Test

One of the IMViC tests to distinguish members of Enterobacteriaceae

Simmons Citrate agar slants. 

Positive: Slant turns blue with growth on slant, OR just growth. Organism utilizes citrate.

Negative: No growth on slant. Does not utilize citrate. 

Mannitol Salt Agar (MSA)

Positive: Yellow growth or halo is S. aureus.  Ferments mannitol. 

Red growth with no halo is Staph, but not aureus.

No growth indicates it isnt a Staph (so growth inhibited by NaCl)

MacConkey Agar

Differentiates Gram + and Gram -

Good growth means Gram-.  

Pink/red growth (may have participate) produces acid from lactose fermentation so probably coliform.

Growth that isn't pink/red does not ferment lactose. Noncoliform. 

Eosin Methylene Blue Agar

Used to isolate fecal coliforms

Growth indicates Gram-. 

Pink/Mucoid growth is a probably a fecal coliform that ferments lactose w/ little acid (slow) production. 

"Colorless" growth (no pink, purple, metallic sheen) is possible coliform that ferments lactose/sucrose with fast acid production

"Colorless" growth (not red/pink) does not ferment lactose/sucrose, noncoliform.  

Hektoen Enteric Agar (HEA)

Used to isolate salmonella and shigella from other enterics

Growth indicates Gram-.

Pink/orange growth is produces acid from lactose fermentation and is not salm/shig

Blue-green growth with black precipitate doesn't ferment lactose but reduces sulfur to H2S: Salmonella

Blue-green growth with no participate doesn't ferment lactose or reduce sulfur: Shigella

DNase test.

Clearing around growth indicates organism secrets exoenzyme DNase that break down DNA.

No clearing opposite.

Used to distinguish some species from others..

Phenylethyl Alcohol Agar (PEA)

Used to isolate staph and strep from specimens with a mixture of flora

Good growth: probable staph, strep, enterococcus or lactococcus. not inhibited by phenylethylalcohol

Selective for Gram+

Triple Salt Iron Agar

Used to differentiate members of Enterobacteriacaea

Yellow slant and butt - glucose and lactose fermentation with acid accumulation

Red slant/yellow butt - glucose fermentation with acid production, proteins catabolized aerobically in the slant with alkaline products

Red slant and butt - no fermentation. peptone catabolized with alkaline products. Not a Entero

Red slant/no change in butt - no fermentation, not a entero

No change at all - not an entero, no fermentation

black participate in the agar - sulfur reduction.

cracks in or lifting of agar - gas production