Development of polymerase chain reaction assays specific for individual pathogenic Aeromonas species

The genus Aeromonas, a group of Gram-negative bacilli, inhabits a wide variety of aquatic environments, including rivers, lakes, and coastal seas. Among Aeromonas species, A. hydrophila, A. caviae, A. veronii, and A. dhakensis are clinically important species that cause infections in humans, leading to diarrhea associated with gastroenteritis, necrotizing fasciitis, and sepsis. A. dhakensis is a newly established species that was reclassified in 2013, and it is considered more pathogenic than other Aeromonas species. However, accurate identification of Aeromonas species by biochemical characteristics, mass spectrometry, and 16S rRNA gene analysis can sometimes be difficult. In this study, 24 strains were classified into nine species by homology and phylogenetic analysis of the RNA polymerase B subunit gene (rpoB), the gold standard method for identifying Aeromonas species. The results of 16S rRNA gene analysis were consistent with those of rpoB analysis for all strains. The results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry were consistent with those of rpoB analysis for all strains excluding A. dhakensis; however, all five A. dhakensis strains were misidentified as other species. Therefore, we attempted to develop species-specific polymerase chain reactions (PCR) for four pathogenic Aeromonas species. The results of these PCRs were completely consistent with those of rpoB gene analysis. These PCR-based methods can permit the identification of pathogenic Aeromonas species, especially A. dhakensis, more quickly and simply than conventional methods.