Bacteriophages in sputum of cystic fibrosis patients as a possible cause of in vivo changes in serotypes of Pseudomonas aeruginosa.

Twenty sputum samples from cystic fibrosis patients were examined for contents of free bacteriophages. Thirty-nine Pseudomonas aeruginosa strains from twenty-seven sputum samples were examined for spontaneously-released phages and mitomycin-induced phages. All of these phages were tested for their ability to change serotype, phage type and resistance pattern of the clinical Pseudomonas strains. Nine of the phages were able to cause change of serotype but not change in phage type or resistance pattern. The mitomycin-induced phages lysed more strains than the spontaneously released phages, while the free phages lysed the highest number of Pseudomonas strains.