Fluorescence-based DNA fingerprinting elucidates nosocomial transmission of phenotypically variable Pseudomonas aeruginosa in intensive care units.

DNA fingerprinting based on automated laser fluorescence analysis of randomly amplified polymorphic DNA (RAPD-ALFA) is a rapid and convenient technique for detecting clonal relatedness of bacterial isolates of nosocomial concern. During an outbreak of Pseudomonas aeruginosa among five patients in a medical intensive care unit, transmission was not suspected because of the phenotypic variability of the initial isolates. However, DNA fingerprinting by RAPD-ALFA and macrorestriction analysis identified a single genotype (strain A) for isolates from three patients and another genotype (strain B) for isolates from the remaining two patients. Strain A isolates displayed three phenotypes defined by different antibiotypes and distinct colony appearance. Retrospective analysis of DNA fingerprints demonstrated that strain A had been transmitted to the index patient one year previously in a different intensive care unit. The study demonstrates that genetic typing approaches are warranted should epidemiological relatedness be identified between phenotypically variant pathogens. Automated laser fluorescence analysis of PCR fingerprints may facilitate routine screening of bacterial isolates for in-house epidemiological surveillance. Antibiograms are an unsuitable approach for the typing of Pseudomonas aeruginosa.