English: Pseudomonas aeruginosa is a nonfastidious, Gram-negative (Fig. J), oxidase postive (Fig. H), nonfermenting rod. P. aeruginosa produces pyoverdin, a water-soluble yellow-green pigment (Fig. A, C, D1, D2). Many P. aeruginosa strains also produce the blue pigment pyocyanin (Fig. B, F). When pyoverdin combines with pyocyanin, the bright green color characteristic of P. aeruginosa is created (Fig. C). Some strains rarely produce other pigments: brown pyomelanin (D3) or red pyorubrin (D4). For the isolation and presumptive identification from clinical and environmental samples a selective agar containing cetrimide can be used (Fig. G).

Fig. A, B Trypticase soy agar (B: P.aeruginosa + S.aureus), Fig. C, D, I Mueller-Hinton agar Fig. E Larger colonies of P. aeruginosa and smaller colonies of Enterococcus faecalis on tripticase soy agar. Reflected light. Fig. F Bluish colonies of P. aeruginosa, yellow colonies of S. aureus and white colonies of Enterococcus faecalis on trypticase soy agar.

Fig. I Plaques are frequently found in freshly isolated strains, especially in the area of confluent growth. In some strains these are caused by phage, in others by bacteriocins.