Selective medium for Pseudomonas aeruginosa that uses 1,10-phenanthroline as the selective agent

Abstract

The MIC of 1,10-phenanthroline for 35 Pseudomonas aeruginosa strains was 128 to 160 μg/ml, whereas 32 μg or less per ml inhibited all other microorganisms tested. On the basis of these results, a selective agar for P. aeruginosa which contained 15 g of Trypticase soy broth (BBL Microbiology Systems), 15 g of agar, and 0.1 g of phenanthroline per liter was formulated. Forty-four P. aeruginosa strains yielded a mean efficiency of plating on this medium of 79% of the counts obtained on Trypticase soy agar, which was significantly higher than that obtained with pseudomonas isolation agar on Pseudosel agar. Pseudomonas cepacia, Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas stutzeri, representatives of 13 other genera (including gram-negative rods, gram-positive rods, and cocci), and a yeast were not recovered within 48 h at 35°C when approximately 107 CFU were plated on this medium. Only small colonies from one strain each of P. fluorescens and P. putida could be seen at 3 and 7 days, respectively, and they had an efficiency of plating of only <0.001%. When 107 CFU of either of these strains was plated with 102 CFU of P. aeruginosa, it did not interfere with the quantitative recovery of P. aeruginosa.