Phe362Tyr in AChE: A Major Factor Responsible for Azamethiphos Resistance in Lepeophtheirus salmonis in Norway

PLoS One. 2016 Feb 16;11(2):e0149264. doi: 10.1371/journal.pone.0149264. eCollection 2016.

Abstract

Organophosphates (OP) are one of the major treatments used against the salmon louse (Lepeophtherius salmonis) in Norwegian salmonid aquaculture. The use of OP since the late 1970s has resulted in widespread resistant parasites. Recently, we reported a single mutation (Phe362Tyr) in acetylcholinesterase (AChE) as the major mechanism behind resistance in salmon louse towards OP. The present study was carried out to validate this mechanism at the field level. A total of 6658 salmon louse samples were enrolled from 56 different fish farms across the Norwegian coast, from Vest Agder in the south to Finnmark in the north. All the samples were genotyped using a TaqMan probe assay for the Phe362Tyr mutation. A strong association was observed between areas with frequent use of the OP (azamethiphos) and the Phe362Tyr mutation. This was confirmed at 15 sites where results from independently conducted bioassays and genotyping of parasites correlated well. Furthermore, genotyping of surviving and moribund parasites from six bioassay experiments demonstrated a highly significant negative correlation between the frequency of resistance alleles and the probability of dying when exposed to azamethiphos in a bioassay. Based on these observations, we could strongly conclude that the Phe362Tyr mutation is a major factor responsible for OP resistance in salmon louse on Norwegian fish farms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcholinesterase / genetics*
  • Amino Acid Substitution*
  • Animals
  • Biological Assay
  • Copepoda / drug effects
  • Copepoda / enzymology*
  • Copepoda / genetics
  • Genotype
  • Insecticide Resistance / drug effects*
  • Logistic Models
  • Mutation / genetics
  • Nonlinear Dynamics
  • Norway
  • Organothiophosphates / toxicity
  • Phenylalanine / genetics*
  • Spatial Analysis
  • Tyrosine / genetics*

Substances

  • Organothiophosphates
  • Tyrosine
  • Phenylalanine
  • azamethiphos
  • Acetylcholinesterase

Grants and funding

The study was financially supported by the Norwegian Research Council through the centre for Innovation Sea Lice Research Centre, grant number NFR 203513/O30. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. This funding organisation did not play any role in the study design, data collection and analysis, decision to publish or preparation of the manuscript and provided only financial support in the form of salaries to Kiranpreet Kaur and Tor Einar Horsberg. The specific roles of all the authors are articulated in the 'author contributions' section. One of the authors of the study is from a commercial company called PatoGen Analyse AS, who contributed in sample collection, running of TaqMan Probe assay and compilation of data for analysis. Moreover, this author did not play any role in the study design, statistical data analysis or the decision to publish.