Investigation of an outbreak of Pseudomonas putida using antimicrobial susceptibility patterns, pulsed-field gel electrophoresis of genomic DNA and restriction fragment length polymorphism of PCR-amplified rRNA operons.

Seventeen Pseudomonas putida isolates were investigated which were collected from the urine specimens of 14 patients and one reflectrometer by comparing antimicrobial susceptibility patterns, pulsed-field gel electrophoresis (PFGE) of genomic DNA, and restriction fragment length polymorphism (RFLP) of PCR-amplified rRNA operons. Three susceptibility patterns were defined by testing 22 antimicrobial agents, with 14 isolates resistant to all agents. PFGE of XbaI-genomic DNA fragments divided the 17 isolates into 9 distinct types. One type, seen in 6 isolates showing identical patterns of approximately 35 fragments of 10 to 350 kb, was defined as the outbreak strain. Another 4 types, in a total of 6 isolates, were considered closely related to the outbreak strain; 2 types in 1 isolate each were possibly related to the outbreak strain; and 2 types in a total of 3 isolates were different from the outbreak strain. All 12 outbreak or closely related isolates were from patients in the surgical intensive care unit and a surgical ward, and were different from isolates in other wards, clearly indicating an outbreak of P. putida. Only two types were defined by the RFLP of 4.5 kb PCR-amplified rRNA operons; one type was seen in 15 isolates, while the other was seen in only 2 isolates. In conclusion, PFGE of genomic DNA is a highly discriminatory and reproducible method for epidemiological typing of P. putida.