An evaluation of the use of three phenotypic test-systems for biochemical identification of Enterobacteriaceae and Pseudomonadaceae

Different methods are available for the phenotypic identification of Enterobacteriaceae and Pseudomonadaceae and in this study, three commercial systems, the Api® 20E-system, the Microbact™ 24E-system, and the Biolog system, were compared. One hundred and nine strains isolated from 72 samples of mixed salads, 23 clinical isolates and 14 reference strains were identified with the three systems. Identification of the 109 isolates from ready-to-eat salads was unsatisfactory. Serious problems occurred when using the Api® 20E-system which identified 19 strains incorrectly as Enterobacter sakazakii, Acinetobacter baumannii, and Acinetobacter haemolyticus were often identified when using the Microbact™ 24E-system. These identifications were not confirmed by the other systems. Difficulties in the evaluation with both systems were mostly encountered with variations in the colour and thus interpretation of the results. The Biolog system often led to multiple identifications for one strain. The identification results of the 23 clinical isolates and the 14 reference strains were more satisfactory, despite the described problems. It could be shown that biochemical identification of Enterobacteriaceae and Pseudomonadaceae with these three systems can only be accepted with reservation.