Nalidixic Acid Cetrimide Agar

A New Selective Plating Medium for the Selective Isolation of Pseudomonas aeruginosa

Abstract

Attempts were made to modify the formula devised by Brown and Lowbury (1965) for more effective selection of Pseudomonas aeruginosa. An improved formula was devised by the authors as follows: Peptone (Eiken) 2.0%, dipotassium phosphate 0.03%, magnesium sulfate (anhydrous) 0.03%, cetrimide 0.02%, nalidixic acid 15 μg/ml, agar 1.5%, with a final pH 7.4-7.6. On this media the growth and pigment production of Ps. aeruginosa was nearly equal to that of Brown-Lowbury's composition. Strains of Enterobacteriaceae such as Klebsiella, Proteus and Providencia were strongly suppressed on the author's medium although some of them showed a moderate growth on BrownLowbury's medium.