24A genetic re-identification of seven Aeromonas blood isolates revealed that phenotype-based 25 identification systems misidentified 5 (71.4%) isolates. In Aeromonas strains, A. aquariorum 26 was the most common misidentified-organism and showed the most potent cytotoxic 27 activities against human blood cell lines, suggesting that the correct identification of A. 28 aquariorum is important. 29 30 / 12The genus Aeromonas is comprised of oxidase-positive, glucose-fermenting, gram-negative 31 rods that are widely distributed in freshwater, estuarine and marine environments and causes 32 a variety of human illnesses such as enterocolitis and septicemia (Figueras, 2005; Janda & 33 Abbott, 2010; Morinaga, et al., 2011). We previously reported that Aeromonas septicemia 34 occurred frequently in hospitalized patients with underlying diseases including malignancy in 35 Japan (Morinaga, et al., 2011). Phenotypical differentiation of the genus Aeromonas or its 36 species has been recognized to be difficult because of the non-uniform biochemical reactions, 37and can lead to misidentification (Abbott, Cheung, & Janda, 2003; Aravena-Roman, Harnett, 38 Riley, Inglis, & Chang, 2011; Figueras, 2005; Figueras, Beaz-Hidalgo, Senderovich, Laviad, 39 & Halpern, 2011). The acid production from arabinose and the production of urocanic acid 40 and sodium dodecyl sulfate have been proposed for discriminating A. aquariorum from other 41 species (Esteve, Alcaide, & Blasco, 2012), but the molecular identification has been 42 emphasized as an alternative method for the correct identification (Figueras, Beaz-Hidalgo, 43 Collado, & Martínez-Murcia, 2011; Puthucheary, Puah, & Chua, 2012). To examine the 44 clinical importance of the correct identification, we molecularly re-identified the isolates 45 included in our previous report and evaluated the virulence genes and cytotoxicity on human 46 cell lines. 47Seven Aeromonas strains recovered from 7 cases with septicemia (one strain did not 48 regrowth) (Morinaga, et al., 2011) were re-identified by sequencing the rpoD gene using 49 4 / 12 primers and conditions previously described (Soler, et al., 2004). The sequences obtained 50 were independently aligned using Mega5 program with the sequences of the type and 51 reference strains of all members of the genus Aeromonas taken from our in-house data base 52 (A. J. Martinez-Murcia, et al., 2011). Percentage similarity was calculated using the Ez 53Taxon pairwise alignment tool (Chun, et al., 2007). Genetic distances and clustering were 54 determined using Kimura's two parameter model (Kimura, 1980) and the evolutionary tree 55 was constructed by the neighbour-joining method (Saitou & Nei, 1987) / 12The cytotoxicity was expressed as the median lethal dose (LD 50 ) of triplicate 87 experiments (Table 1)