Unusual mechanism of pathogenicity of Pseudomonas aeruginosa isolates from patients with cystic fibrosis.

A Pseudomonas aeruginosa strain was isolated from a patient with cystic fibrosis and was found capable of growing within polymorphonuclear leucocytes. As illustrated by electron microscopy, several mechanisms accounted for the intracellular growth: (a) Cell division occurred within the lysosomes; (b) The fusion of the phagosome with the primary lysosome was inhibited; (c) The phagosomal membrane disintegrated, and the bacteria grew within the cytosol; (d) Cytosolic material was separated from the surroundings by bacterial membranes, and subsequently the bacteria coated with host material were released from the leucocyte. The patient suffered from several severe acute pulmonary exacerbations as long as the intracellularly growing variant was detectable in his sputum. After the strain had been eliminated by antibiotic therapy the patient improved (from stage two to one).