Inhibition of Pseudomonas aeruginosa from cystic fibrosis by selective media.

Pseudomonas Isolation Agar (selective agent, Irgasan, 25 mg/1) and Pseudomonas Selective Agar (selective agents, cetrimide 200mg/1 and nalidixic acid 15 mg/1) inhibited some strains of P aeruginosa from cystic fibrosis sputum but did not inhibit isolates from other sources. Of 200 cystic fibrosis isolates, 22 were inhibited by 16 mg/1 Irgasan, 45 by 8 mg/1 nalidixic acid, and 15 by 128 mg/1 cetrimide. We recommend that cystic fibrosis sputum should be cultured on selective and non-selective media to maximise the isolation of P aeruginosa.