A selective medium for enumeration and recovery of Pseudomonas cepacia biotypes from soil

Abstract

TB-T medium provides a high degree of selectivity for and detection of Pseudomonas cepacia biotypes upon initial plating from soil. TB-T medium consists of a basal medium with glucose as the sole carbon source and asparagine as the sole nitrogen source. The selectivity of TB-T medium is based on the combination of trypan blue (TB) and tetracycline (T) (pH 5.5). On TB-T medium, 216 of 300 isolates (72%) from five different soil types were identified as P. cepacia. The remaining 28% were facultative organisms that could be separated readily from P. cepacia by anaerobic glucose fermentation and by their inability to grow at 41 degrees C. Molds were controlled on low soil dilutions by adding crystal violet, nystatin, or both. Elimination of either ingredient or elevation of the pH to 7.5 resulted in a pronounced loss of selectivity. The efficiency of recovery varied considerably among P. cepacia strains but was high enough for some strains (76 to 86%) to permit quantitative studies. TB-T medium combines a defined formulation with high selectivity and allows recovery of P. cepacia biotypes from low soil dilutions (10(1) to 10(3)).