Blysine Iron Agar Test

Intended Use • Lysine Iron Agar is used for the differentiation of enteric organisms based on their ability to decarboxylate or deaminate lysine and to form hydrogen sulfide  Components: 

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Lysine deamination • Reaction in the slant  Lysine

decarboxylation • Reaction in the butt

Lysine deamination

is an aerobic process which occurs on the slant of the media  If the bacterium can deaminate Lysine in the slant, it will produce an unknown orange product  This orange product will react with the Brom-cresol Purple  If the organism has the ability to deaminate lysine, the ammonia produced will react with the ferric ammonium citrate to produce a dark red color on the slant of the tube (Positive deamination: red slant) (Negative deamination:  purple slant)  The genus that will give a positive red slant are Proteus, Providencia, Citrobacter and Morganella 

is an anaerobic process which occurs in the butt of the media  Due to overneutralizing the acid formed from glucose fermentation  The bacteria that is inoculated into the butt of this tube can ferment the glucose, producing a low or acidic pH 

This induces the bacteria to form the carboxylase enzyme which removes the -COOH from the lysine molecule, creating an amine end product, that is alkaline in pH 

If the organism has the ability to decarboxylate lysine, it produces an amine end-product which reacts with the pH indicator to give a purple color in the butt of the tube (Positive decarboxylation: purple butt) (Negative decarboxylation:  yellow butt)

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Organisms which produce hydrogen sulfide gas will exhibit a black precipitate in the butt of the tube



LIA is not as reliable an indicator of H2S as are KIA and TSI

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Splitting of the agar in the butt indicates gas production.

Procedures:

Inoculate the organism into the Lysine Iron Agar medium Stab the butt twice all the way down, then streak the slant using a straight wire needle Incubate at 37OC for 18-24 hours.

SLANT P/P

- /+

purple slant lysine deaminase negative

P/Y

-/-

purple slant lysine deaminase negative

R/Y

+/-

red slant lysine deaminase positive

BUTT purple butt lysine decarboxylase positive yellow butt lysine decarboxylase negative yellow butt

lysine decarboxylase you cannot have a + slant with a + butt! negative