Identification of Gram-negative non-fermenters and oxidase-positive fermenters by the Oxi/Ferm Tube

Abstract

Since the recent introduction of the Roche Oxi/Ferm Tube to the UK two identification schemes have been developed by the manufacturer for use with the kit. We evaluated the success of these two schemes in identifying 222 predominantly culture collection strains belonging to 45 taxa of non-fermenters and nine taxa of oxidase-positive fermenters. The strains were chosen to represent all the taxa included in the two identification schemes developed by the manufacturer and we have therefore been able to assess the overall success of identification by the two schemes. Since, however, our choice of strains does not reflect their incidence in clinical material, our identification rates are not necessarily those that might be obtained in a routine clinical laboratory. The most advanced identification scheme so far developed for the Oxi/Ferm Tube (CCIS System 1977-1432) allowed 62% of the 222 strains to be correctly identified although a disturbing feature was that more of the strains that were not correctly identified were incorrectly identified (24%) rather than not identified (14%); these figures represent an improvement over the earlier identification scheme (CCIS System 1976-621-74346) for which the corresponding figures were 56%, 32%, and 12%. CCIS System 1977-1432 seems likely to give a better performance in a routine clinical laboratory than in this study since for those taxa which, we would judge from the material sent to us for identification, are most commonly seen in a routine laboratory (Acinetobacter calcoaceticus, A. lwoffii, Pseudomonas aeruginosa, P. fluorescens, P. maltophilia, P. pseudoalcaligenes, and P. putida) 89% were correctly identified, none remained unidentified, and 11% were incorrectly identified. Thirty strains, each of a different taxon, were tested in triplicate to assess the reproducibility of reactions in the Oxi/Ferm Tube.