Evaluation of Biolog system for identification of some gram-negative bacteria of clinical importance

The Biolog system (Biolog, Inc., Hayward, Calif.) was evaluated for the identification of 55 gram-negative taxa (789 strains) likely to be encountered commonly in clinical laboratories. The Biolog system performed best with oxidase-positive fermenters and biochemically active nonfermenters and had the most problems with unreactive nonfermenters. It gave significantly better results when the MicroPlates were read manually rather than when they were read by the automated reader. Plates read manually gave the following performances: oxidase-positive fermenters, five taxa, 64 strains, 92% correct, 3% not identified, and 5% incorrect; biochemically active nonfermenters, eight taxa, 122 strains, 88% correct, 6% not identified, and 6% incorrect; members of the family Enterobacteriaceae, 35 taxa, 511 strains, 77% correct, 8% not identified, and 15% incorrect; unreactive nonfermenters, seven taxa, 92 strains, 38% correct, 24% not identified, and 38% incorrect. We found the system easy to use, but while for 39 of 55 of the taxa an identification rate of > 70% was achieved, problems were encountered, particularly with identification of capsulated strains of some Enterobacter and Klebsiella taxa, as well as the least biochemically active Moraxella and Neisseria strains.