Pyrorubrin-producing Pseudomonas Aeruginosa.

Pyrorubrin, a red pigment produced by some Pseudomonas aeruginosa cultures, was first described by Meader, Robinson, and Leonard (Amer. J. Hyg. 5:682, 1925). The object of this note is to record the incidence of pyrorubrinforming strains in clinical material and the more frequent occurrence of these strains in urinary isolates of P. aeruginosa. During an investigation in which different typing methods were applied to P. aeruginosa, 688 strains isolated in 24 hospitals in the United Kingdom and other countries were examined for their ability to produce pyrorubrin on stock nutrient agar plates. Formation of red diffusible pigment was recorded after 16 hr of incubation at 37 C and an additional 24 hr at room temperature. The determination of the sero-pyocine type was useful in that only the first pyrorubrinproducing strain isolated in a ward of a particular hospital and belonging to a certain type was included. This policy would provide better identified as P. aeruginosa by the following reactions: oxidation of gluconate and production of slime within 3 days at 37 C; good growth at 42 C; growth on tetraphenyl tetrazolium chloride agar and cadmium sulfate agar; production of proteolytic enzymes (gelatinase and collagenase); production of pyocines; slide-agglutination with polyvalent P. aeruginosa antiserum. The details of these tests are presented elsewhere (Wahba and Darrell, J. Gen. Microbiol., in press). As shown in Table 1, the overall incidence of pyrorubrin-forming strains was 3.5%, and the largest number of these strains was isolated from urine (58.3% of the total). Their more frequent occurrence in the sero-pyocine types A/2 and D/6 does not appear to be significant, as these two types are among the most common ones in any large series (Darrell and Wahba, J. Clin. Pathol. 17:236, 1964). Strains producing pyrorubrin did not appear to produce pyocyanin and vice versa.