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:

Lysine deamination• Reaction in the slant

Lysine decarboxylation• Reaction in the butt

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

Lysine deamination

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)

Organisms that can decarboxylate lysine :Salmonella, Klebsiella, Enterobacter, Serratia

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

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 BUTT

P/P - /+ purple slantlysine deaminase negative

purple buttlysine decarboxylase positive

P/Y - / - purple slantlysine deaminase negative

yellow buttlysine decarboxylase negative

R/Y + / - red slantlysine deaminase positive

yellow buttlysine decarboxylase negative

you cannot have a + slant with a + butt!