TYPING OF STRAINS FROM A SINGLE-SOURCE OUTBREAK OF PSEUDOMONAS-PICKETTII

Plasmid profiles, genome restriction fragment polymorphisms, carbohydr ate oxidation-fermentation reactions, methylumbelliferyl substrate hyd rolysis patterns, antimicrobial susceptibilities, and results obtained with the Biolog GN biochemical substrate kit were used to type 19 com mon-source, but mixed-biotype, outbreak strains and one epidemiologica lly distinct strain of Pseudomonas pickettii. Biotyping with conventio nal and methylumbelliferyl substrates failed to distinguish between st rains. Plasmid profile testing was found to be inconsistent and not re producible. The Biolog GN kit allowed greater strain differentiation t han restriction fragment polymorphism did (12 biotypes versus 5 biotyp es); antimicrobial susceptibility testing yielded 4 biotypes, and oxid ation-fermentation tests gave 3 biotypes. Oxidation-fermentation resul ts were consistent with restriction fragment polymorphs in all but 1 o f the 20 strains tested. For ease of typing, comprehensive typeability , and reproducibility, oxidation-fermentation tests should be performe d initially and followed if necessary by restriction fragment polymorp h analysis for the elucidation of P. pickettii infection outbreaks.