Comparison of the Minitek system with conventional methods for identification of nonfermentative and oxidase-positive fermentative gram-negative bacilli.

The Minitek system was compared with conventional test methods for identifying a wide range of nonfermentative and oxidase-positive fermentative gram-negative bacilli. A total of 230 isolates representing 33 species and biotypes were tested against 12 Minitek substrates and the corresponding conventional tube media. In addition, supplementary tests were included for 141 (61.3%) of the isolates. Overall, 88% of the positive reactions agreed, and negative reactions agreed 95.5%. Anaerobic dextrose, maltose, lactose, and citrate were responsible for 62.4% of the 93 discrepant positive reactions, and 51.8% of the 83 discrepant negative reactions involved the aerobic dextrose, nitrate, and citrate disks. Some discrepancies were related to specific organisms. The system and supplementary tests correctly identified 88.3% of the isolates to species level and 92.6% to correct genus. No particular organism or substrate was responsible for misidentification errors. In a test challenge with 19 selected organisms, 3 were incorrectly identified to species and 4 were misidentified to genus level. Most of the errors responsible for these incorect identifications were due to factors other than the Minitek disks and pointed out the importance of using appropriate supplemental data, and the need for a coding manual and a more enriched broth for certain types of isolates.