A dual approach employing MALDI-TOF MS and real-time PCR for fast species identification within the Enterobacter cloacae complex

A real-time PCR procedure targeting the gene of the molecular cochaperon DnaJ (dnaJ) was developed for specific detection of strains belonging to the Enterobacter cloacae group. The inclusivity and exclusivity of the real-time PCR assay were assessed with seven reference strains of E. cloacae, 12 other Enterobacter species and 41 non-Enterobacter strains. Inclusivity as well as exclusivity of the duplex real-time PCR was 100%. In contrast, resolution of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) was inadequate for delineation of Enterobacter asburiae, Enterobacter hormaechei, Enterobacter kobei and Enterobacter ludwigii from E. cloacae. Eleven of 56 (20%) clinical isolates of the E. cloacae group could not be clearly identified as a certain species using MALDI-TOF MS. In summary, the combination of MALDI-TOF MS with the E. cloacae-specific duplex real-time PCR is an appropriate method for identification of the six species of the E. cloacae complex.