The genus Aeromonas comprises primarily aquatic bacteria and also serious human and animal pathogens with the occurrence in clinical material, drinking water, and food. Aeromonads are typical for their complex taxonomy and nomenclature and for limited possibilities of identification to the species level. According to studies describing the use of MALDI-TOF MS in diagnostics of aeromonads, this modern chemotaxonomical approach reveals quite high percentage of correctly identified isolates. We analyzed 64 Aeromonas reference strains from the set of 27 species. After extending the range of analyzed Aeromonas species by newly described ones, we proved that MALDI-TOF MS procedure accompanied by Biotyper tool is not a reliable diagnostic technique for aeromonads. We obtained quite high percentage of false-positive, incorrect, and uncertain results. The identification of newly described species is accompanied with misidentifications that were observed also in the case of pathogenic aeromonads.

When MALDI-TOF MS profiling of bacteria is used for strain discrimination, the cultivation conditions should be properly optimized and controlled as they significantly contribute to the discriminatory power of the method.

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Fluorescent Pseudomonas putida CCM 3656 (ATCC 11250) was analysed according to the methods of polyphasic approach which were based on sequence analyses involving the rpoB and rrs genes, manual ribotyping using endonuclease HindIII, DNA base composition determination and DNA-DNA hybridization. The results obtained by these genotyping methods showed that the strain CCM 3656 is distant from P. putida taxon, which was supported with phenotype characterization represented by whole-cell protein profile analysis, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry profiling and extended biotyping. The DNA-DNA hybridization experiments performed between the strain CCM 3656 and the closest relatives revealed 77 % similarity with Pseudomonas jessenii. However, the outcomes of sequencing, ribotyping and phenotype characterization allow distinguishing the studied strain from P. jessenii. On the basis of the obtained taxonomic data, we suggest reclassifying strain CCM 3656 to a novel subspecies of P. jessenii and propose naming P. jessenii subsp. pseudoputida subsp. nov. with CCM 3656(T) as type strain. Furthermore, we present an amended description of P. jessenii and proposal of P. jessenii subsp. jessenii subsp. nov.