title: Tetracycline resistance genes persist at aquaculture farms in the absence of selection pressure.
abstract: The prophylactic and therapeutic use of tetracyclines in aquaculture has been shown to contribute to the spread of tetracycline resistance in the environment. In this work, the prevalence of four different tetracycline-resistance genes, tetA, tetC, tetH, and tetM, in sediments from four aquaculture farms and their surroundings in the Baltic Sea was monitored by quantitative polymerase chain reaction (qPCR). The presence of three additional tetracycline-resistance genes (tetE, tetG, and tetW) was studied qualitatively by standard PCR, and the amount of bioavailable tetracyclines and total amounts of tetracycline and oxytetracycline in samples were also measured. None of the farms were using tetracycline at the time of the sampling and one of the farms had stopped all antibiotic use six years prior to the first sampling. Two of the farms were sampled over four successive summers and two were sampled once. Our results showed greater copy numbers of tetA, tetC, tetH, and tetM at the farms compared to pristine sites and demonstrated the presence of tetE, tetG, and tetW genes in the sediments under aquaculture farms at most sampling times. However, no resistance genes were found in samples collected 200 m from any of the farms. None of the samples contained therapeutically active concentrations of tetracyclines at any of the sampling times, suggesting that the increase in the prevalence of tetracycline resistance genes is caused by the persistence of these genes in the absence of selection pressure.
authors.affiliation: Department of Food and Environmental Sciences, University of Helsinki, Helsinki, Finland. manu.tamminen@helsinki.fi
authors.forename: Manu
authors.initials: M
authors.lastname: Tamminen
authors.forename: Antti
authors.initials: A
authors.lastname: Karkman
authors.forename: Andres
authors.initials: A
authors.lastname: Lõhmus
authors.forename: Windi Indra
authors.initials: WI
authors.lastname: Muziasari
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takasu
authors.forename: Shigeki
authors.initials: S
authors.lastname: Wada
authors.forename: Satoru
authors.initials: S
authors.lastname: Suzuki
authors.forename: Marko
authors.initials: M
authors.lastname: Virta
mesh_terms: D017920:Antiporters / Q000032:analysis; D017756:Aquaculture; D001419:Bacteria / Q000235:genetics; D001426:Bacterial Proteins / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D015373:Bacterial Typing Techniques; D005798:Genes, Bacterial; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction; D012097:Repressor Proteins / Q000032:analysis; D012623:Seawater / Q000737:chemistry / Q000382:microbiology; D012641:Selection, Genetic; D013752:Tetracycline / Q000032:analysis / Q000378:metabolism / Q000633:toxicity; D013753:Tetracycline Resistance / Q000235:genetics*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism / Q000633:toxicity
chemical_list: D017920:Antiporters; D001426:Bacterial Proteins; D012097:Repressor Proteins; C107173:TetC protein, Bacteria; D014874:Water Pollutants, Chemical; C079051:tetA protein, Bacteria; D013752:Tetracycline