Differential primary plating medium for enhancement of pigment production by Pseudomonas aeruginosa

A cost-effective and more rapid means of detection of Pseudomonas aeruginosa in cultures from clinical specimens would be very advantageous. We have developed a modified MacConkey agar (MMA), which enhances pigment production of P. aeruginosa and which, if pyocyanin pigment is present, provides a relatively rapid and very cost-effective identification. The MMA medium inhibits the gram-positive organisms, while lactose- and non-lactose-fermenting gram-negative rods are easily distinguishable from pigment-producing pseudomonads. Organisms that produce pyocyanin, pyoverdin, or pyorubin, or both pyocyanin and pyoverdin, are easily recognized on the medium. Pyocyanin production is clearly distinguishable from other Pseudomonas pigments on MMA. In a comparative study, MMA identified 97% of the P. aeruginosa strains 24 h earlier than routine laboratory biochemical methods. Highly mucoid strains which did not produce detectable pigments on standard biochemicals produced detectable pigments on the MMA within 48 h. This medium can provide a very practical, reliable, and cost-effective means for early characterization of P. aeruginosa.