Accuracy and reproducibility of the Oxi/Ferm system in identifying a select group of unusual gram-negative bacilli

Abstract

The Oxi/Ferm (O/F) identification system was compared in a double-blind study to a conventional test battery for the characterization of 96 reference and clinical strains consisting of 83 nonfermentative and 13 oxidase-producing, fermentative gram-negative bacilli. The O/F tube and supplemental tests correctly identified 84% of the nonfermentative and 77% of the oxidase-producing, fermentative bacilli. When the supplemental tests were excluded and the biochemical profiles generated by all 9 O/F tube reactions were examined, the profile accuracy reached 95% (79 of 83) of the nonfermentative and 93% (12 of 13) for oxidase-producing, fermentative bacilli. Of the 9 O/F substrate reactions, 7 demonstrated .gtoreq. 89% agreement with conventional reactions, whereas the urea and arginine reactions provided 82 and 85% agreement, respectively. Replicate O/F tests with 6 selected organisms demonstrated 97% identification reproducibility and 84% overall substrate reproducibility. The mean O/F identification time was 2.6 days as compared to 3.3 days for the conventional system. Although the O/F system is a convenient, rapid and accurate alternative to conventional identification methods, several modifications are recommended.