Molecular phylogenetic and matrix-assisted laser desorption ionization time-of-flight mass spectrometry identification of isolates from horses identified as Enterobacter cloacae by biochemical identification.

Enterobacter cloacae is an opportunistic pathogen of horses. Thirty isolates obtained from horses and their environments and identified as Enterobacter cloacae by biochemical methods were reidentified by taxonomic identification based on multilocus sequence analysis (MLSA) and by a commercial identification system based on matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). MLSA identified the 30 equine isolates as E. ludwigii (9/30), E. asburiae (1/30), or E. cloacae (1/30); 19 isolates were not identified. The MALDI-TOF MS system could not clearly distinguish isolates to the species level, and the limited numbers of reference spectra for Enterobacter species might have contributed to the poor identification.