Phylogenetic analysis of the pathogenic genus Aeromonas spp. isolated from diseased eels in China

Analyses of 16S rRNA and housekeeping genes (HKGs) were valuated as identification markers for pathogenic Aeromonas isolated from diseased eels. The interrelationships of 32 Aeromonas strains which had been verified as pathogens to eels were studied using phylogenetic analysis with 16S rRNA and HKG sequences (cpn60, gyrB, rpoB and dnaJ) and identified by Biolog automatic microbiology analysis system (gene III). From the analysis of 5 genes, the mean gene divergences of 16S rRNA, cpn60, gyrB, rpoB and dnaJ in 32 isolates were 1.4 ± 0.2%, 7.1 ± 0.7%, 5.2 ± 0.5%, 2.2 ± 0.4% and 6.8 ± 0.5%, respectively. The results of comparative phylogeny between nucleotide based analyses (excluding the third codon position) of four HKGs with the sequences from 55 strains of Aeromonas (including 23 referenced strains of Aeromonas) showed cpn60 and dnaJ have higher discriminate power than gyrB and rpoB comparing with the taxonomical identification by Biolog system. In addition, amino acid sequences of concatenated cpn60-rpoB-gyrB is a good method for Aeromonas pathogens identification. This study showed analysis of HKG sequences can be used as an alternative method for sound identification of bacterial pathogens isolated from diseased eels in China.