Molecular study of a false outbreak of ticarcillin-resistant Pseudomonas aeruginosa infections in a clinical hematology department.

Molecular methods for bacterial strain typing are becoming available outsid e teaching hospitals and large structures. Although it seems reasonable to use conventional markers, most notably the serotype, whenever possible, the limitations of these methods are particularly conspicuous with P. aerugino sa. Combined use of several methods such as quantitative antibiotic suscept ibility testing and serotype determination has proved adequate for characte rizing P. aeruginosa strains in some cases. In the case of the outbreak rep orted herein, this approach failed to provide high quality epidemiological data. In contrast, pulsed field gel electrophoresis ruled out epidemic spre ad of a P. aeruginosa strain in the clinical hematology department.