Numerial Taxonomy and DNA-DNA Hybridizations of Aeromonas strains Isolated from Human diarrhoeal Stool, Fish and Environment

Abstract

Summary A numerical taxonomic study and DNA-DNA hybridizations were performed on seventy-one isolates of Aeromonas collected from children diarrhoeal stool, dead and alive fish Rutilus rutilus, and environment. These isolates were compared with the fifteen type and reference strains of the presently recognized Aeromonas genomic species. Results of the phenotypic tests were analysed by numerical taxonomic techniques, using the simple matching coefficient (SSM) and Jaccard coefficient (SJ), and the unweighted average linkage clustering (UPGMA). At SSM > 85% and SJ > 75% these analyses resolved 6 groups and 9 single strains. DNA-DNA hybridization experiments revealed seven genomic groups among the examined Aeromonas isolates. Clusters were identified as A. hydrophila/A. bestiarum (two groups), A. veronii biotype sobria (two groups), A. caviae/A. medial A. eucrenophila, and A. media. The results obtained with the numerical taxonomy were not in perfect agreement with the DNA-DNA hybridization results and showed genetic heterogeneity of some phena. In some cases strains of one genomic species were found in different clusters or one cluster contained more than one hybridization group (HG). Among isolates of HG 8/10 biovariants were found. Strains of HG 1–3 and of HG 4–6 showed high phenotypic homogeneity. The results of this study emphasise the need to use of molecular methods in addition to phenotypic characteristics for identification of Aeromonas isolates with the genomic species.