USEFULNESS OF THE API-20E SYSTEM FOR THE IDENTIFICATION OF BACTERIAL FISH PATHOGENS

A total of 223 isolates belonging to motile Aeromonas, A. salmonicida, Vibrio anguillarum, Pasteurella piscicida and Yersinia ruckeri specie s were tested by the API-20E system and the results compared with thos e obtained with standard biochemical tube and plate tests. Depending o n the species, the API-20E yielded false negative and positive reactio ns for fermentation of different sugars, lysine decarboxylase (LDC), V oges Proskauer (VP), citrate and gelatinase reactions. Thirteen of 32 (41%) A. salmonicida strains and 9 of 53 (17%) Y. ruckeri isolates wer e correctly identified using the API index. Forty-five of 69 (65%) mot ile Aeromonas tested (including 34 A. hydrophila, 10 A. sobria and 1 A . caviae strains) were identified as A. hydrophila. The low discrimina tion profiles generated by 9 Yersinia and 2 motile Aeromonas isolates were avoided using the supplementary tests cited in the API index. In the case of V. anguillarum and P. piscicida, which are not at present included in the API-20E system, 35 of 53 strains of V. anguillarum wer e wrongly identified as A. hydrophila, and all the P. piscicida isolat es were incorrectly identified as Pseudomonas fluorescens/Ps. putida. A large number of isolates, including some reference strains, produced uncoded profiles. From these results, we consider that the API-20E sy stem will be a useful tool for field diagnosis of bacterial fish disea ses if its database is expanded to include V. anguillarum, P. piscicid a, A. sobria and A. caviae species and the new profiles generated by s trains of species already considered. In addition, some reactions nece ssary to discriminate between strains which share the same profile num ber are proposed.