Evaluation of the Rapid ID 32A system for identification of anaerobic Gram‐negative bacilli, excluding the Bacteroides fragilis group

Objective: To evaluate the Rapid ID 32A system (bioMérieux, Marcy‐l'Etoile, France) for the identification of anaerobic Gram‐negative bacilli, excluding the Bacteroides fragilis group. Methods: Five hundred and twenty‐eight identified clinical isolates of non‐B. fragilis group anaerobic Gram‐negative bacilli were tested in the Rapid ID 32A system, and identifications were compared with those obtained with conventional biochemical tests and gas‐liquid chromatography. Results: The Rapid ID 32A system correctly identified 280 (60.9%) of the 460 isolates tested for which taxa were included in the database, without the need for additional testing. A further 97 (21.1%) isolates were correctly identified to species level following the performance of complementary tests recommended by the manufacturer. Fifty‐nine (12.8%) isolates were identified at the genus level only, and 21 (4.6%) were misidentified at the species level. Three isolates of Prevotella were not identified by the system. Of the 68 isolates belonging to taxa not included in the database, no identification was obtained for 33 (48.5%), while 35 (51.5%) were misidentified. Conclusions: The Rapid ID 32A system provided a rapid and reliable method for the identification of non‐B. fragilis group, anaerobic Gram‐negative bacilli to the genus level, while the success of species‐level identification varied with different taxa. There was poor discrimination between Fusobacterium nucleatum and F. necrophorum, between Porphyromonas asaccharolytica and Porphyromonas endodontalis, and between Prevotella buccalis, Prevotella denticola, Prevotella loescheii, Prevotella melaninogenica and Prevotella oralis. The need to perform conventional complementary tests on 149 (32.4%) of the 460 isolates compromised the usefulness of the system for rapid species identification.