The Chilean salmon industry has undergone a rapid development making the country the world’s second largest producer of farmed salmon, but this growth has been accompanied by an intensive use of antibiotics. This overuse has become so significant that Chilean salmon aquaculture currently has one of the highest rates of antibiotic consumption per ton of harvested fish in the world. This review has focused on discussing use of antibiotics and current status of scientific knowledge regarding to incidence of antimicrobial resistance and associated genes in the Chilean salmonid farms. Over recent years there has been a consistent increase in the amount of antimicrobials used by Chilean salmonid farms, from 143.2 tons in 2010 to 382.5 tons in 2016. During 2016, Chilean companies utilized approximately 0.53 kg of antibiotics per ton of harvested salmon, 363.4 tons (95%) were used in marine farms, and 19.1 tons (5%) in freshwater farms dedicated to smolt production. Florfenicol and oxytetracycline were by far the most frequently used antibiotics during 2016 (82.5 and 16.8%, respectively), mainly being used to treat Piscirickettsia salmonis, currently considered the main bacterial threat to this industry. However, the increasing development of this industry in Chile, as well as the intensive use of antimicrobials, has not been accompanied by the necessary scientific research needed to understand the impact of the intensive use of antibiotics in this industry. Over the last two decades several studies assessing antimicrobial resistance and the resistome in the freshwater and marine environment impacted by salmon farming have been conducted, but information on the ecological and environmental consequences of antibiotic use in fish farming is still scarce. In addition, studies reporting the antimicrobial susceptibility of bacterial pathogens, mainly P. salmonis, have been developed, but a high number of these studies were aimed at setting their epidemiological cut-off values. In conclusion, further studies are urgently required, mainly focused on understanding the evolution and epidemiology of resistance genes in Chilean salmonid farming, and to investigate the feasibility of a link between these genes among bacteria from salmonid farms and human and fish pathogens.

The taxonomic position of a chlorophenol-degrading bacterium, strain S37^T, was investigated. The 16S rDNA sequence indicated that this strain belongs to the genus Sphingopyxis, exhibiting high sequence similarity to the 16S rDNA sequences of Sphingomonas alaskensis LMG 18877^T (98·8 %), Sphingopyxis macrogoltabida LMG 17324^T (98·2 %), Sphingopyxis terrae IFO 15098^T (95 %) and Sphingomonas adhaesiva GIFU 11458^T (92 %). These strains (except Sphingopyxis terrae IFO 15098^T, which was not investigated) and the novel isolate accumulated polyhydroxyalkanoates consisting of 3-hydroxybutyric acid and 3-hydroxyvaleric acid from glucose as carbon source. The G+C content of the DNA of strain S37^T was 65·5 mol%. The major cellular fatty acids of this strain were octadecenoic acid (18 : 1ω7c), heptadecenoic acid (17 : 1ω6c) and hexadecanoic acid (16 : 0). The results of DNA–DNA hybridization experiments and its physiological characteristics clearly distinguished the novel isolate from all known Sphingopyxis species and indicated that the strain represents a novel Sphingopyxis species. Therefore, the species Sphingopyxis chilensis sp. nov. is proposed, with strain S37^T (=LMG 20986^T =DSM 14889^T) as the type strain. The transfer of Sphingomonas alaskensis to the genus Sphingopyxis as Sphingopyxis alaskensis comb. nov. is also proposed.