Identification of enterococcus species isolated from commercial fish feeds and infected fish specimens

Abstract

The genus of lactic acid bacteria Enterococci are Gram-positive cocci bacterium that can survive in different environmental conditions such as water, plants, and soil. They are also bacteriological signs of fecal contamination. In aquaculture facilities, Enterococcus species have appeared as one of the crucial opportunistic fish pathogens. Enterococcus-caused fish diseases have been reported in different fish species like yellow tail, turbot, and tilapia. Even though Enterococcus species are used as probiotics and are members of the gastrointestinal flora, they also have pathogenic potential to produce septicemia, wound infections, urinary tract infections, and others. In this study, we isolated bacterial strains from affected rainbow trout and trout feed specimens. Based on the API 20 strep test kit, they were determined as Enterococcus faecium. While fish-isolated samples had 74.4%-99.9% similarity to E. faecium, trout feed isolated samples had 98.4%-99.9% similarity to E. faecium. In order to identify the isolates of the trout feed, PCR was performed using universal 16S rRNA primers. Sequence results indicate that the samples were E. faecium and E. faecalis. The phylogenetic tree was constructed with other Enterococcus species of 16S rRNA, and our samples were located in the E. faecium and E. faecalis species. In conclusion, there may be contamination of Enterococcus with food or other factors. Enterococcus sp. strains are opportunistic microorganisms and cause pathogenicity when the host immunity weakens. Even though all samples with API 20 strep test kit were identified as E. faecium, they had the lower percentage similarity, so they may be E. faecalis and other Enterococcus species. Thus, further studies are needed to understand their probiotic and pathogenicity functions in aquaculture production.