Characterization and phylogenetic analysis of a Aeromonas veronii clinical strain isolated from blood culture

Objective To identify an unknown pathogenic strain (X1) isolated from blood culture of an inpatient and to conduct a phylogenetic analysis on it. Methods The X1 strain was isolated from blood culture of an inpatient in the Second Xiangya Hospital of Central South University in 2016. It was identified by morphology biochemical testing and 16S rRNA gene sequencing. Based on genetic distances, a phylogenetic tree was constructed to compare the X1 strain with its homologous species in GenBank in order to reveal its genetic evolution. Results The X1 strain was gram-negative. Biochemical testing for oxidase, glucose and V-P reaction were positive (+ ), while the result of citrate was negative (-). Sequence alignment analysis of 16S rRNA showed that the X1 strain (1 466 bp) was highly homologous with Aeromonas veronii X71120.1 with a similarity of more than 99%. Genetic distances between the X1 strain and its homologous species, including Aeromonas veronii, Aeromonas hydrophila and Aeromonas sobria, were calculated by MEGA5.0 and the results revealed that the genetic distance (0.014) between it and Aeromonas veronii X71120.1 was the shortest, but the subspecies of it was unable to identify. Cluster analysis also indicated that the X1 strain and Aeromonas veronii were clustered to a small branch. Conclusions The X1 isolate was an Aeromonas veronii strain. Besides, Aeromonas veronii and Aeromonas sobria were similar in genetic characteristics. Key words: Aeromonas veronii; Identification; 16S rRNA; Phylogenetic tree