Ribotyping of Pseudomonas aeruginosa from infected patients: evidence of common strain types.

Sixty-nine strains of Pseudomonas aeruginosa isolated from infected patients at three hospitals in Valencia were serotyped and analyzed by comparison of restriction fragment length polymorphisms of ribosomal RNA genes (ribotyping). Genomic Southern blots of EcoRI restriction digests were hybridized with a universal rRNA gene probe from Escherichia coli 16S and 23S rRNA. Strains were genetically diverse and 12 different ribotypes of 2 to 7 bands between 5 and 21.5 kb were defined. All strains shared a common band of 6.0 kb. The predominant ribotypes were R1 and R2, representing 25% and 41% of all isolates, respectively. Ribotypes were not consistently associated with serotypes, but they clearly subtyped strains of the same serotype. This study demonstrated the prevalence of certain strain types associated with infected patients at Valencia hospitals, confirming the high typability and reproducibility of a single enzyme ribotyping for epidemiological studies of Pseudomonas aeruginosa. Ribotyping could be particularly useful if used in conjunction with serotyping.