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.

Antibacterial Drugs in Fish Farms: Application and Its Effects

“…Tetracycline-resistance genes are found even in small farms which rarely use antibacterials. The copy numbers of tetA, tetC, tetH, and tetM genes (tetR reported by Seyfried et al, (2010)) remain elevated at farms over the surveillance period of four years in the absence of any selection pressure from tetracycline or even other antibacterials (Schmitt & Römbke, 2008;Tamminen et al, 2010). The continued introduction of tetracycline-resistant organisms from the hatchery to the stream, even after a significant time period had elapsed since the use of antibacterials, indicates the presence of reservoirs of organisms or unknown sources of resistance (Stachowiak et al, 2010) as well as other aquatic bacteria, and also illustrates that these bacteria can act as reservoirs of resistance genes that can be further disseminated.…”

“…The presence of feed residue in the aquatic system would have an important effect for the generation and maintenance of the drug resistance of bacteria in sediment (Yu et al, 2009). These results call for the development of better management strategies for fish farming so as to prevent the emergence of resistant gene pools in the sediments of aquaculture facilities, and to promote the disappearance of established resistant gene pools (Tamminen et al, 2010). Principles for the prudent use of antibacterials should be developed and awareness of the problem of antibacterial resistance should be raised by informing the public (FAO, 2005).…”

Removal of antibiotics and antibiotic resistance genes from domestic sewage by constructed wetlands: Optimization of wetland substrates and hydraulic loading

“…Use of antibiotics in humans and animals could also lead to development and spread of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the environment (Pruden et al, 2006;Tao et al, 2010;Su et al, 2012). Therefore, antibiotics and ARGs have been regarded as emerging environmental contaminants and detected in diverse environmental compartments (Tamminen et al, 2010;Su et al, 2012;Cheng et al, 2013;Coleman et al, 2013). It is found that ARGs can be disseminated among bacteria via vertical and horizontal gene transfer, and distributed from human and animal sources to receiving environment .…”

Removal of antibiotics and antibiotic resistance genes from domestic sewage by constructed wetlands: Effect of flow configuration and plant species

“…Previous studies have reported wide detection of various antibiotics and ARGs in effluent and sludge from wastewater treatment plants (WWTPs), which could be a major cause for the ubiquitous occurrence of antibiotics and ARGs in various environmental compartments (Pruden et al, 2006;Durham et al, 2010;Li and Zhang, 2010;Tamminen et al, 2011;Gao et al, 2012;Jia et al, 2012;Su et al, 2012;Cheng et al, 2013;Coleman et al, 2013;Zhou et al, 2013). Therefore, a better wastewater treatment technology is needed for removing antibiotics and ARGs.…”