[Pyocine typing of Pseudomonas aeruginosa strains from nosocomial outbreaks - after the elimination of possible sources of mistakes by heat-treatment (author's transl)].

In 25% of the freshly cultivated Pseudomonas aeruginosa strains (isolated from nosocomial infections) a change of the pyocine type determined according to the method of Gillies and Govan results from passages on selective or non-selective media or from several days' storage at room temperature (Tab. 1 and 2). This inconstancy of the pyocine type can be avoided by exposure of the strains to 56 degrees C for 5-75 min. After this heat treatment the agarose-gel-electrophoresis of the strains shows the loss of all non-conjugative plasmids smaller than 25 kbp (Fig. 2). By typing more than 1,000 strains from nosocomial Pyocyaneus outbreaks we could demonstrate the reliability of the pyocine typing after having cured the strains by heat. Further we propose a binary numbering system for the pyocine types using the results of the 8 indicator strains (Tab. 3).