Comparison of two selective media developed to isolate Pseudomonas cepacia from patients with cystic fibrosis.

Two media selective for Pseudomonas cepacia have been described recently: OF-polymyxinbacitracin-lactose agar (OFPBL) and P. cepacia agar (PCA). We compared these by culturing sputum from 27 patients with cystic fibrosis. Sputum from each patient was studied using streak-plate (SP) and quantitative (Q) culture methods. Five strains of P. cepacia were isolated from four patients (15%). P. cepacia was not found on routine media by SP or Q methods in three of the four patients. All five isolates grew on both OFPBL and PCA and all were recovered by SP and Q culture methods. Colony counts of P. cepacia obtained by Q cultures were similar on both selective media. Each of the selective media allowed the growth of other organisms; nineteen of 27 specimens cultured on OFPBL yielded non-P. cepacia spp. and six of 27 specimens cultured on PCA yielded non-P. cepacia spp. species (p less than 0.005). Pseudomonas aeruginosa was isolated from 26 of 27 patients on routine media (96%). This organism was recovered from four specimens cultured on OFPBL but from none on PCA (p less than 0.05). OFPBL and PCA are both selective for P. cepacia and enhance the ability to recover this organism from patients with cystic fibrosis using either SP or Q cultures of sputum; however, PCA is significantly more inhibitory for non-P. cepacia spp. than OFPBL.