Assessing the probiotic potential of Lactococcus lactis isolated from the intestine and gill of rainbow trout (Oncorhynchus mykiss) through in vitro analysis

Abstract

The emergence of diseases and the indiscriminate use of antibiotics have had deleterious consequences in the aquaculture industry. Consequently, the growing emphasis on eco-friendly alternatives has taken center stage, and probiotics have emerged as a notable solution. This investigation aimed to identify and characterize potential probiotic bacteria present in the gills and intestine of rainbow trout (Oncorhynchus mykiss (Walbaum)). A total of 29 isolates were selected for in vitro evaluation. The assays included morphological evaluation, catalase, oxidase, hemolysis, pathogen antagonism, antimicrobial susceptibility, protease, and amylase tests. Seven isolates exhibited antagonism against one of the three pathogens tested (Aeromonas hydrophila, Streptococcus agalactiae, and Lactococcus garvieae). None of the isolates showed resistance to the antibiotics ampicillin, florfenicol, or tetracycline. Furthermore, all isolates showed proteolytic but not amylolytic activity. The isolates with the best characteristics were identified as Lactococcus lactis (n=7) by 16S rRNA gene sequencing.