Relationship between clinical and environmental isolates of Pseudomonas aeruginosa in a hospital setting

Populations of Pseudomonas aeruginosa have been extensively studied, although there is no general agreement concerning their genetic structure. It has been proposed that P. aeruginosa is a very homogeneous species with 90% of individuals within the same clonal group; nonetheless, other results suggested that Pseudomonas populations are panmictic. Here we compared P. aeruginosa populations from clinical and environmental samples, both isolated from the Bellvitge Hospital of the University of Barcelona in Spain.

Antibiotic susceptibility determination as well as whole cell and outer membrane protein denaturing gel electrophoresis, pulsed-field electrophoresis, and random amplified polymorphic DNA analysis were performed.

Environmental isolates were much more susceptible to antibiotics than those isolated from clinical specimens. The remainder of the analyses revealed high degree of diversity.

Whole-cell proteins, outer-membrane proteins, and pulsed field electrophoresis did not support a close relationship between clinical and environmental isolates. Random amplified polymorphic DNA (RAPD) confirmed the distance between isolates from both sources. This suggests that the origin of hospital infections by P. aeruginosa is due mainly to growth of bacterial strains acquired by patients prior to hospital admission or from patient-to-patient through healthcare workers (HCWs).