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Raoultella ornithinolytica is an encapsulated Gram-negative, oxidase-negative, catalase-positive, aerobic, non-motile rod that belongs to the Enterobacteriaceae family. This bacterium was initially classified in the genus Klebsiella as Klebsiella ornithinolytica, until the creation of the genus Raoultella in 2001. R. ornithinolytica is usually found in water environments and soil, and due to its ability to convert histidine to histamine, it has been associated with histamine poisoning in humans. R. ornithinolytica is an emerging entity in human infections, with several reports of virulent infections in comorbid at-risk patients. Increasing reports are potentially due to better and more precise identification tools. The objective of this article is to provide a comprehensive review of reported cases of R. ornithinolytica infections, the emergent virulence of described multiresistant strains, and an overview of currently used identification methods.

Raoultella Planticola is a gram-negative, non-motile, anaerobic bacterium of the Genus Raoultella most commonly found in water, soil, and aquatic environments1 Originally classified as a member of the genus Klebsiella, it was reclassified as Raoultella spp. in 2001 based on 16S rRNA and rpoB gene sequencing.1 This bacterium is a rare source of infection in humans; current literature provides few serious cases. The first Raoultella invasive human infection was found in 1984 in a patient with sepsis.2 Most reported cases since then have been associated with bacteremia. We present a case of R. Planticola in a patient with UTI, as well as a review of prior reported cases of R. Planticola associated with cystitis. There is weak evidence for susceptibility to R. Planticola cystitis; risk factors include immunosuppression, invasive procedures, and contaminated equipment3, 4, 5, Table 2. Table 2 References.

Background: Raoultella is a Gram-negative bacteria, which commonly occur in the natural environment such as water, soil and on plants. In recent years, Raoultella spp. gained more interest. There is also an increasing number of publications describing mainly clinical cases involving these bacteria. Identification of Raoultella spp. is difficult due to a phylogenetic relationship with Klebsiella spp. Purpose: Available biochemical tests do not always allow for their identification to species. Thus, the aim of this study was to evaluate selected methods of identification of Raoultella spp. and their differentiation from genus Klebsiella. Materials and Methods: In this evaluation three methods were used such as manual test ID32E (bioMérieux), automatic test VITEK2 Compact (bioMérieux) and matrix-assisted laser desorption ionisation-time of flight mass spectrometry (MALDI-TOF MS) method (Bruker). Results: Good identification of the species was obtained for 81.4% of the strains in the ID32E test, 93.3% in VITEK2 Compact test, and 97.4% in MALDI-TOF MS method, respectively. Conclusion: It was established that MALDI-TOF MS method is reliable in identifying genus Raoultella.

Rapid and reliable identification of microorganisms in the clinical laboratory is essential for an early and accurate diagnosis guiding timely therapy. However, conventional methods are sometimes unreliable and show controversial outcomes. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been reported as a rapid and reliable method for identification of bacteria and fungi isolated from clinical samples. Members of the genus Raoultella are increasingly recognized as clinically relevant. There are difficulties in their identification at the species level since sequencing the 16S rRNA or the rpoB genes does not show conclusive results. The aim of this study has been to compare two MALDI-TOF MS systems (Vitek MS and Bruker Biotyper) with Vitek2 and API20E systems for differentiation of Raoultella species. A collection of 97 clinical isolates of Raoultella species was identified with Vitek MS, in parallel with Vitek2 and API, and finally with Bruker Biotyper. Among the two most widely used MALDI-TOF MS platforms, results obtained with Vitek MS were slightly superior to those obtained with the Bruker Biotyper system, with sensitivities and specificities of 98.9/57.9% and 98.8/37.0%, respectively. The current commercial phenotypic identification systems are not optimized for the identification of Raoultella species. Our results indicate that MALDI-TOF-based identification is more accurate and sensitive than that provided by phenotypic methods.

The genus Raoultella was excised from Klebsiella in 2001, but difficulties in its identification may have led to an underestimation of its incidence and uncertainty on its pathogenic role. Recently, clinical reports involving Raoultella have increased, probably through the introduction of mass-spectrometry in clinical microbiology laboratories and the development of accurate molecular techniques. We performed a retrospective analysis using our blood culture collection (2011-14) to identify Raoultella isolates that could have been erroneously reported as Klebsiella. PCR and gene sequencing of highly specific chromosomal class A β-lactamase genes was established as the reference method, and compared with 16S rRNA and rpoβ sequencing, as well as matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS), MicroScan Walkaway system and API20E biochemical identification. MALDI-TOF and rpoβ correctly identified all Raoultella isolates, whereas 16S rRNA provided inconclusive results, and MicroScan and API20E failed to detect this genus. The analysis of the clinical characteristics of all Raoultella bacteraemia cases reported in the literature supports the role of Raoultella as an opportunistic pathogen that causes biliary tract infections in elderly patients who suffer from some kind of malignancy or have undergone an invasive procedure. Two salient conclusions are that Raoultella shows tropism for the biliary tract and so its identification could help clinicians to suspect underlying biliary tract disease when bacteraemia occurs. Concomitantly, as most phenotypic identification systems are not optimized for the identification of Raoultella, the use of MALDI-TOF or additional phenotypic tests is recommended for the reliable identification of this genus.

We report here the emergence of seven IMP-4-producing Raoultella ornithinolytica isolates obtained from one patient. All isolates carried the bla IMP-4 carbapenemase gene, five isolates also carried bla SHV-12 , four contained bla TEM-1 , and one contained bla OXA-1 . Notably, the R. ornithinolytica isolate Ro25724 also expressed Klebsiella pneumoniae carbapenemase (KPC)-2. The bla KPC-2 gene was located on a Tn 3 -Tn 4401 integration structure on a plasmid of ∼450 kb. This is the first description of the coexistence of bla KPC-2 and bla IMP-4 from the genus Raoultella .

The genus Raoultella is composed of Gram-negative, aerobic, oxidase-negative, catalase-positive, nonmotile, capsulated rods belonging to the Enterobacteriaceae family ([1][1]). Raoultella ornithinolytica is found in aquatic and hospital environments ([2][2]). Occurrence of Raoultella in human