Evaluation of accuracy and repeatability of identification of food-borne pathogens by automated bacterial identification systems.

The performances of five automated microbial identification systems, relative to that of a reference identification system, for their ability to accurately and repeatedly identify six common food-borne pathogens were assessed. The systems assessed were the MicroLog system (Biolog Inc., Hayward, Calif.), the Microbial Identification System (MIS; MIDI Inc., Newark, Del.), the VITEK system (bioMérieux Vitek, Hazelwood, Mo.), the MicroScan WalkAway 40 system (Dade-MicroScan International, West Sacramento, Calif.), and the Replianalyzer system (Oxoid Inc., Nepean, Ontario, Canada). The sensitivities and specificities of these systems for the identification of food-borne isolates of Bacillus cereus, Campylobacter jejuni, Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., and verotoxigenic Escherichia coli were determined with 40 reference positive isolates and 40 reference negative isolates for each pathogen. The sensitivities of these systems for the identification of these pathogens ranged from 42.5 to 100%, and the specificities of these systems for the identification of these pathogens ranged from 32.5 to 100%. Some of the systems had difficulty correctly identifying the reference isolates when the results were compared to those from the reference identification tests. The sensitivity of MIS for the identification of S. aureus, B. cereus, E. coli, and C. jejuni, for example, ranged from 47.5 to 72. 5%. The sensitivity of the Microlog system for the identification of E. coli was 72.5%, and the sensitivity of the VITEK system for the identification of B. cereus was 42.5%. The specificities of four of the five systems for the identification of all of the species tested with the available databases were greater than or equal to 97.5%; the exception was MIS for the identification of C. jejuni, which displayed a specificity of 32.5% when it was tested with reference negative isolates including Campylobacter coli and other Campylobacter species. All systems had >80% sensitivities for the identification of Salmonella species and Listeria species at the genus level. The repeatability of these systems for the identification of test isolates ranged from 30 to 100%. Not all systems included all six pathogens in their databases; thus, some species could not be tested with all systems. The choice of automated microbial identification system for the identification of a food-borne pathogen would depend on the availability of identification libraries within the systems and the performance of the systems for the identification of the pathogen.