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

Ruiz L, Escribano C, Vinuesa T, and Viñas M

Microbiology Unit. Department of Pathology and Experimental Therapeutics. University of Barcelona. Campus de Bellvitge. Feixa Llarga s/n 08907. Hospitalet de Llobregat. Barcelona. Spain. lidiaruizm@ub.edu

Populations of P. aeruginosa have been extensively studied although there is not 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 but other results suggested that Pseudomonas populations are panmictic. Here we compare P. aeruginosa populations from clinical and environmental samples isolated both from the Bellvitge Hospital.

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 rest of the analyses revealed a high degree of diversity. Whole-cell proteins, outer-membrane protein and pulsed field electrophoresis did not support a close relationship between clinical and environmental isolates. RAPD confirmed the distance between the isolates from both sources.

This suggests that the origin of hospital infections by P. aeruginosa are mainly due to the growth of bacterial strains acquired by patients prior to admission to hospital or from patient-to-patient through health care workers (HCWs).