DECARBOXYLASE BASE BROTH (Moeller)

Base for amino acid decarboxylation tests.

Code: CB1/5672M

Typical formula g/l

Peptone	5.00
Beef extract	5.00
Pyridoxal	0.005
Glucose	0.50
Bromocresol purple	0.01
Cresol red	0.005

pH 6.0 +/- 0.1

Description

Decarboxylase Base Broth M is the base used for amino acid decarboxylation tests for the identification of Enterobacteriaceae. Arginine, lysine and ornithine are converted to the correspondent amines.

Directions

Suspend 10.5g of Moeller Broth Base in 1000ml of cold distilled water heat to dissolve, add L-amino acids in a final concentration of 1% (w/v); if necessary readjust the pH. Distribute in 1-1.5 ml amounts in small tubes, seal with sterile liquid paraffin and sterilise at 121^{_{°C for 15 minutes.}}

Method

The three sets of tubes containing respectively the three amino acids are inoculated with the organism by using a needle, covered with 4-5ml of mineral oil and incubated at 37°C for 4 days. Carry out the relevant checks by using tubes inoculated without the amino acids and daily check the colour change of the medium in all the tubes. Moeller medium contains bromocresol purple and bromocresol red and is violet coloured; Falkow medium contains only bromocresol purple and is purple coloured. Glucose present in both media is fermented by all the enterobacteria with colour change of the indicator system from violet to yellow. The medium, when made acidic, allows the amino acid decarboxylation reactions with formation of amines (cadaverine from lysine, putrescine from arginine and ornithine). These amines make the medium alkaline and cause a new colour change of the indicator from yellow to violet or purple. The negative reaction is therefore given by the appearance of a yellow colour in the tube, the positive reaction by a violet or purple colour. The following table summarises the reactions given by a few organisms.

Microorganisms Lysine Ornithine Arginine

Escherichia coli + var. var.

Enterobacter cloacae + +

Enterobacter aerogenes + + -

Edwardsiella tarda + + -

Salmonella typhi + - var.

Citrotacrer treundi - var. var.

Proteus vulgaris - - -

Proteus mirabilis - + -

Shigella dysenteriae - -

Shigella sonnei + -

Serratia liquefaciens var. - -

Serratia marcescens + + -

Klebsiella pneumoniae - + -

User quality assurance (37°C-48 h with mineral oil)

Positive control

Decarboxylase Medium + Lysine: S.marcescens ATCC 81100

Decarboxylase Medium + Lysine: S.marcescens ATCC 13124

Decarboxylase Medium + Arginine: E.cloacae ATCC 13047

Negative control

Decarboxylase Medium + Lysine: E.cloacae ATCC 13047

Decarboxylase Medium + Lysine: K.pneumoniae ATCC 23357

Decarboxylase Medium + Arginine: P.mirabilis ATCC 25933

Storage

Dehydrated media: 15-30°C

User prepared tubes: 1 month at 2-8°C

References

Cowan and Steel’s Manual for Identification of Medical Bacteria, 2nd edition. Cambrige: University Press, 1974.

Moeller V. (1955) - Acta Path. Microbiol. Scand., 36, 158.