Typing of strains from a single-source outbreak of Pseudomonas pickettii

Plasmid profiles, genome restriction fragment polymorphisms, carbohydrate oxidation-fermentation reactions, methylumbelliferyl substrate hydrolysis patterns, antimicrobial susceptibilities, and results obtained with the Biolog GN biochemical substrate kit were used to type 19 common-source, but mixed-biotype, outbreak strains and one epidemiologically distinct strain of Pseudomonas pickettii. Biotyping with conventional and methylumbelliferyl substrates failed to distinguish between strains. Plasmid profile testing was found to be inconsistent and not reproducible. The Biolog GN kit allowed greater strain differentiation than restriction fragment polymorphism did (12 biotypes versus 5 biotypes); antimicrobial susceptibility testing yielded 4 biotypes, and oxidation-fermentation tests gave 3 biotypes. Oxidation-fermentation results were consistent with restriction fragment polymorphs in all but 1 of the 20 strains tested. For ease of typing, comprehensive typeability, and reproducibility, oxidation-fermentation tests should be performed initially and followed if necessary by restriction fragment polymorph analysis for the elucidation of P. pickettii infection outbreaks.