Arginine dihydrolase medium

Purpose

Used to distinguish the Pseudomonas syringae group from other Pseudomonas spp.

Ingredients

Ingredient	500 ml	250 ml
Distilled water	500 ml	250 ml
Bacto peptone	0.5 g	0.25 g
NaC1	2.5 g	1.25 g
K2HPO4	0.15 g	0.075 g
Phenol red	0.005 g	0.0025 g
L-Arginine HCL *	5 g	2.5 g
Agar	1.5 g	0.75 g

Instructions

1. Heat to melt the agar and dispense 4 ml per 100 mm disposable tube. Autoclave. The medium should be orange-pink.
2. Stab-inoculate tubes in duplicate then seal one tube with about 1 cm depth of sterile mineral oil. Incubate for 3-7 days at 27 °C depending on original work. The enzyme arginine dihydrolase releases ammonium from arginine. The resulting alkalinity is indicated by the pH indicator phenol red, which turns a dark pink color under oil as opposed to the orange-pink of uninoculated controls. The unsealed inoculated tube will turn pink but is only to serve as a "positive control."

• Use 1% of the L form or 2% of the DL form.

Notes

• Be careful not to let the pH get too high when making the medium. If the medium is too pink (high pH), it may not be possible to discern a positive reaction.

• The enzyme, arginine dihydrolase, releases ammonium from arginine. The resulting alkalinity is indicated by the pH indicator phenol red, which turns a dark pink color under oil as in contrast to the orange pink of uninoculated controls or arginine dihydrolase-negative cultures.

References

• Fahy, P. C., and Persley, G. J. 1983. Plant Bacterial Diseases, A Diagnostic Guide. (p.356). Academic Press, New York. 393 pp.

• Thornley, M. J. 1960. The differentiation of Pseudomonas from other Gram-negative bacteria on the basis of arginine metabolism. Journal of Applied Bacteriology 23:37-52.

Contributed by

From the Culture Media for Plant Pathogenic Fungi and Bacteria, University of Massachusetts: Contributed by Robert L. Wick