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

The performances of five automated microbial identification systems, relati ve to that of a reference identification system, far their ability to accur ately and repeatedly identify six common food-borne pathogens were assessed . The systems assessed were the MicroLog system (Biolog Inc., Hayward, Cali f.), the Microbial Identification System (MIS; MIDI Inc., Newark, Del.), th e VITEK system (bioMerieux Vitek, Hazelwood, Mo.), the MicroScan WalkAway 4 0 system (Dade-MicroScan International, West Sacramento, Calif.), and the R eplianalyzer system (Oxoid Inc., Nepean, Ontario, Canada). The sensitivitie s and specificities of these systems for the identification of food-borne i solates of Bacillus cereus, Campylobacter jejuni, Listeria monocytogenes, S taphylococcus aureus, Salmonella spp., and verotoxigenic Escherichia coli w ere determined with 40 reference positive isolates and 40 reference negativ e isolates for each pathogen. The sensitivities of these systems for the id entification of these pathogens ranged from 42.5 to 100%, and the specifici ties 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 refere nce identification tests. The sensitivity of MIS for the identification of S. aureus, B. cercus, 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 identif ication of B. cereus was 42.5%. The specificities of four of the five syste ms for the identification of all of the species tested with the available d atabases 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 i t 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 lev el. The repeatability of these systems for the identification of test isola tes ranged from 30 to 100%. Not all systems included all six pathogens in t heir databases; thus, some species could not be tested with all systems, Th e choice of automated microbial identification system for the identificatio n of a food-borne pathogen would depend on the availability of identificati on libraries within the systems and the performance of the systems for the identification of the pathogen.