Pathogenic significance of Pseudomonas fluorescens and Pseudomonas putida.

Among the members of the genus Pseudomonas, P. aeruginosa and P. pseudomallei were, until recently, considered the human pathogens. However, since the early 1960s, other Pseudomonas species have been found in clinical specimens, and their number and frequency of isolation seem to be growing.' The "simple fluorescent" species, P. fluorescens and P. putida, belong to those that were thought by earlier authors28 to be nonpathogenic for man. A few instances of possible human pathogenicity, however, have been reported since 1953 when Pittman' described six strains with the characteristics of P. fluorescens that had grown in transfusion blood and had caused severe to fatal reactions in the recipients. Rutenburg et al.' mentioned three urinary tract infections and one wound infection from which P. fluorescens was recovered in pure culture; septicemia developed in the latter case. The authors also reported a mixed urine culture with P. fluorescens. Rogers' cultured P. putida from the blood of an 8-year old boy with a fatal septicemia and otherwise unexplained lymphadenopathy and hepatosplenomegaly. Sutter7 isolated P. fluorescens repeatedly from the blood of a patient with an abdominal abscess following bowel resection. Furthermore, she cultured P. putida from a bile drain, from two urines (in pure culture from an asymptomatic patient and in mixed culture from another patient with chronic urinary tract infection), and from a sputum after pneumococcal pneumonia treated with erythromycin and tetracycline. Pathogenicity of the P. putida strains could not be established in these cases. Pickett et al.' found P. putida in urines of ten patients. Two cultures were pure and came from debilitated patients with no clinical signs of urinary tract infection, while three other strains from different sources as well as 43 strains of P. fluorescens were not considered etiologically significant by these authors. In view of such reports, it is not surprising that there is no unanimity as to the pathogenic significance of P. fluorescens and P. putida for man. This paper is intended as a contribution to the discussion. In the two-year period from March, 1969 to February, 1971, 11 strains of P. putida and 4 strains