Evaluation of an impedance method for subtyping of Pseudomonas aeruginosa

Eight isolates (no. 1 to 8) of Pseudomonas aeruginosa isolated from 8 burn patients were typed by pulsed-field gel electrophoresis (PFGE), arbitrarily primed polymerase chain reaction (PCR) (AP-PCR), biotyping, antimicrobial susceptibility testing, and a newly developed technique-impedance method. By both PFGE and AP-PCR, isolates 1 and 2 were designated type A, while isolates 3 to 8 were designated type B. However, isolates 3 to 8 could be further divided into three distinct subtypes (B, C, and D) by the impedance method. Four antibiograms were obtained by testing the 8 isolates against six antimicrobial agents and designation of antibiogram to each of the 8 isolates was in accordance with those obtained by the impedance method. The results of biotyping did not agree with any of the above typing methods. In conclusion, the impedance technique had a high discriminatory ability to differentiate genetically related clones into subtypes. The method is simple, reproducible, and has a high typeability.