A simple diagnostic milk medium for Pseudomonas aeruginosa.

An agar medium containing 10% defatted milk has been tested as a diagnostic medium for Pseudomonas aeruginosa and, in particular, for differentiating between P. aeruginosa and P. fluorescens. Only P. aeruginosa colonies gave clear zones due to hydrolysis of casein together with diffused green pigment. Results on milk agar correlated well with the pattern of results from a variety of conventional tests used to identify this organism. Pigment production of P. aeruginosa on milk agar was better than on special media commonly used to enhance this characteristic. Routine diagnosis of P. aeruginosa is recommended by streaking on a solid medium containing 10% defatted milk granules, 25% nutrient broth, and 2% agar, and examining for clear zones and pigment after 24 hours' incubation.