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 Patricio Feest

Flavobacterium psychrophilum is a Gram negative bacteria and the etiological agent of cold water disease and rainbow trout fry syndrome in salmon farming. In Chilean aquaculture, its presence was described for the first time in 1993. Despite the severe impact of this disease, antimicrobial therapy is the only method currently available to control this condition in farmed fish, however, overuse of antibiotics in aquaculture has caused an alarming increase in resistant bacteria.

According to the study, one of the main factors influencing the bacterial resistance to antibiotics is the ability of bacteria to form biofilms. "When a pathogenic bacterium lives in a heterogeneous biofilm, biocides and antibiotics have no visible effect, so that a concentration of various magnitudes to eliminate pathogens that inhabit a biofilm is needed," said researcher and co-author of the scientific work, Dr Homero Urrutia.

"Many Antarctic researches with bacteria have focused on the search for antimicrobial compounds, because the Antarctic microorganisms have developed unique strategies for survival as the secretion of extracellular compounds to reduce interspecific competition, giving them a competitive advantage," said the research team.

The aim of the study was to evaluate the effect of extracellular compounds produced by isolates obtained in Antarctica on biofilm formation of F. psychrophilum. To do this, the authors used a total of 67 supernatants from Antarctic isolates obtained from surface rocks, the water column, sediment and rhizosphere of mosses collected in the Fildes Peninsula, King George Island and the Chilean Antarctic Territory, during January 2010.

18 of the supernatants obtained (26.9%) strongly inhibited biofilm formation. Of these, the researchers chose the supernatant M19B insulation, which showed the lowest rate of biofilm formation (SBF = 0.19) compared to (SBF = 4.9) in the control.

The isolate M19B provided 99% identity with the species Pseudomonas fragi (GenBank access number AB685646.1). The sequence obtained in this work (824 bp) was entered in the GenBank access code KC854411.

The importance of this study lies in the high mortality seen in Chilean salmonids associated with F. psychrophilum (Flavobacteriosis) which represents around 8.5% of the total losses with infectious cause in 2014, ranking as the sixth leading cause of mortality at the fry stage (according to information from the Technological Institute of Salmon, Intesal).