Antimicrobial activity of bacteriocin‐producing Carnobacterium spp. isolated from healthy Patagonian trout and their potential for use in aquaculture

In this study, bacteria from the intestines of Patagonian trout displaying fish pathogen antimicrobial activity were isolated and characterized. Isolates T4, T15 and M5 showed extracellular antimicrobial activity against the fish pathogen Carnobacterium maltaromaticum CECT 4020, by the agar well diffusion assay. They were identified as Gram-positive catalase-negative bacilli belonging to the genus Carnobacterium (based on 99.93% identity with the 16S rRNA gene sequence of C. maltaromaticum DSM 20342T). After 48 hr of incubation in MRS broth, the highest antimicrobial activity titre (327,680 AU/ml) was recorded for T4, followed by T15 and M5. The antimicrobial agents produced by these isolates were thermostable peptides. LC-MS/MS peptide analysis indicated that T4 and T5 bacteriocins belonged to the class IIa. The identified peptides for T4 bacteriocin included almost the entire divercin V41 sequence, which was previously believed to be exclusively produced by Carnobacterium divergens. In addition, no negative fish health effects were observed after administrating T4 to zebrafish. Among the isolates from healthy Patagonian trout, due to its early bacteriocin production, its greater inhibition titre and its innocuous feature, Carnobacterium sp. T4 emerged as the most promising isolate for in vivo challenges targeting its further aquaculture application.