Antimicrobial resistance and molecular characterization of Pantoea agglomerans isolated from rainbow trout (Oncorhynchus mykiss) fry

Aquaculture has become an important candidate as an animal protein source through its growth over the last decade. Based upon a report from the Food and Agriculture Organization of the United Nations, it is the fastest growing sector of the food industry, yet the pathogenicity of many biological agents involved in aquaculture is still unknown. In this study, we isolated Pantoe agglomerans from diseased rainbow trout on several occasions and also attempted to determine their phenotypic and genotypic characteristics, including antimicrobial resistance, of four bacterial isolates. In the present study, P. agglomerans was isolated from diseased rainbow trout as a pathogenic agent. The identification of the P. agglomerans isolates from the rainbow trout was performed through biochemical tests and 16S rRNA sequence analysis. These isolates were predominately biochemically homogeneous, although some features were different, such as seen in methyl-red, mannose and lipase activity tests. All four studied isolates were identified as 99% identical to P. agglomerans based on sequence analysis. The isolates were compared through a phylogenetic analysis with P. agglomerans sequences recovered from 16 other countries and accessed from the GenBank database. All isolates in our study were at least 98.2% similar to sequences from GenBank. Furthermore, the phenotypic antimicrobial susceptibility of the isolates in this study was analyzed through both disc diffusion and broth micro dilution minimum inhibitory concentration (MIC) tests. Although there were some differences between two phenotypic antimicrobial tests, all studied isolates were found susceptible to different antimicrobials. In addition genotypic antimicrobial resistance characteristics were assessed by the presence of antimicrobial resistance genes (ARGs), in which qnrS and sul2 were detected for the first time in P. agglomerans.