Evaluation of three phenotypic identification systems for clinical isolates of Raoultella ornithinolytica.

Raoultella spp. have recently been separated from the genus Klebsiella based on their molecular characteristics. It was discovered that Raoultella ornithinolytica can be misidentified as Klebsiella oxytoca by commonly used phenotypic identification systems. Therefore, this study evaluated the ability of three phenotypic systems to identify R. ornithinolytica compared with the genotypic methods sequence-specific primer PCR (SSP-PCR), 16S rRNA gene sequence analysis using the MicroSeq 500 system16S rDNA bacterial identification system or comparison with GenBank sequences using blast. The phenotypic systems examined in this study were the VITEK 2 GN ID card, the MicroScan Neg Combo 32 panel and API 20E. The SSP-PCR panel was able to distinguish the R. ornithinolytica reference strain from other Raoultella spp. and K. oxytoca. Of the 27 isolates identified as R. ornithinolytica by SSP-PCR, VITEK 2 identified all of them as R. ornithinolytica. MicroScan and API identified 25 isolates (92.6%) and 24 isolates (88.9%) as K. oxytoca, respectively. These isolates were ornithine decarboxylase (ODC) negative in all three phenotypic systems. MicroSeq 500 identified 24 isolates (88.9%) as R. ornithinolytica, whereas GenBank identification was heterogeneous. Of the 68 isolates identified as K. oxytoca by SSP-PCR, 66 isolates (97.1%) were identified as K. oxytoca by VITEK 2, MicroScan and API. MicroScan and API require additional biochemical tests to differentiate between ODC-negative R. ornithinolytica and K. oxytoca.