Comparison of the Oxi/Ferm and N/F systems for identification of infrequently encountered nonfermentative and oxidase-positive fermentative bacilli.

The N/F system (Flow Laboratories, Inc. Rockville, Md) and the Oxi/Ferm Tube, (Roche Diagnostics, Div. Hoffman-La Roche, Inc. Nutley, N.J.) were evaluated in parallel for identification of infrequently encountered nonfermentative gram-negative bacilli and oxidase-positive, fermentative gram-negative bacilli selected from fresh clinical isolates and stock cultures. When compared with conventional media, the Flow N/F system correctly identified 97.7% (86 or 88) of all strains tested. No organisms were misidentified, but this system failed to identify two strains. Six supplemental tests were needed for the complete identification of 16 strains (18%); however, correct results were obtained within 48 h for 85% of the isolates. The Oxi/Ferm method correctly identified 87.5% of the isolates; 7% were incorrectly identified, and the method failed to identify five strains. Seventeen supplemental tests were required to identify 64 strains (73%). Complete identification within 48 h was obtained for 60% of the organisms tested.