Abstract
Pseudomonas aeruginosa was recovered (in numnbers ranging from 102 to 105 colony-forming units per millilitre) from heavily contaminated hospital waste water when grown at 41.5.degree. C on a differential medium agar containing 9-chloro-9-(4-diethylaminophenyl)-10-phenylacridan (C-390) at a final concentration of 30 .mu.g/mL. The medium appeared to be highly selective for P. aeruginosa with 95-100% of all colonies isolated from four different hospital waste waters being identified as P. aeruginosa. Many strains of P. aeruginosa isolated from hospital waste waters failed to hydrolyse casein when grown on skim milk agar and this medium appeared to restrict pigment production to only pyoverdin (detectable only under ultraviolet light). However, most strains were capable of casein hydrolysis when grown on a modified skim milk medium.