Raoultella spp. - reliable identification, susceptibility to antimicrobials and antibiotic resistance mechanisms.

Introduction. Raoultella spp. representatives are Gram-negative rod-shaped bacteria of the Enterobacteriaceae family. These bacteria are commonly found in the natural environment.Aim. The aim of the study was to indicate the reliable method for Raoultella spp. strains identification, evaluate the susceptibility of Raoultella spp. strains to selected antimicrobials and to detect their resistance mechanisms to beta-lactams.Methodology. Susceptibility of the strains to chosen antimicrobials was determined using the automatic method. The presence of particular antimicrobial resistant mechanism and genes encoding ESBLs and MBLs was determined respectively with double-disc synergy test and commercially available kit - eazyplex SuperBug CRE test (Amplex Diagnostics) and standard PCR. For the selected strains, DNA sequencing was performed.Results. Amongst 105 of the examined Raoultella spp. strains, majority were sensitive to: imipenem (99.0 %), meropenem (98.1 %), gentamicin (93.3 %) and ciprofloxacin (92.4 %). Of the tested Raoultella strains, thirteen (12.4 %) produced ESBLs and one strain simultaneously ESBLs and MBLs. The DNA sequencing results were as follows: for all the reference strains the correct species identification was achieved, for the analysed strains two were identified as R. planticola and one as R. ornithinolytica.Conclusion. Although Raoultella spp. strains remain sensitive to antibiotics, there is a constant need to monitor the sensitivity of these bacteria to selected antimicrobials. Isolation of a multi-drug resistant R. ornithinolytica strain indicates that even the less frequently isolated species of Enterobacteriaceae family should be precisely identified because they might be of clinical importance and the particular strain can also produce enzymes that pose the greatest threat today.