Auxotrophic variants of Pseudomonas aeruginosa are selected from prototrophic wild-type strains in respiratory infections in patients with cystic fibrosis

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Abstract
Twenty-four nutritionally dependent (auxotrophic) Pseudomonas aeruginosa strains were isolated from 20 cystic fibrosis (CF) patients and tested for their amino acid requirements. Two different methods were necessary to identify the nutritional status of all isolates. Methionine was the most common single amino acid required (9 of 24 isolates), followed by leucine and arginine or ornithine. In total, a requirement for 12 different compounds or combination of compounds was demonstrated. Auxotrophic and prototrophic pairs of isolates from the same patient were compared by macrorestriction analysis of DNA in pulsed-field gel electrophoresis. Thirteen of 18 pairs analyzed presented identical restriction fragment length polymorphism profiles following digestion of DNA with XbaI. Three of the remaining pairs showed percentage similarities of 77, 91, and 98%, and the profiles of two pairs could not be compared because of the excessive degradation of their DNA. These results suggest that auxotrophic and prototrophic P. aeruginosa isolates colonizing the same CF patient constitute an isogenic group and raise the possibility that auxotrophs are selected from the prototrophic population during the course of pulmonary infection in CF patients.