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Vancomycin resistant enterococci (VRE) in Swedish sewage sludge

Graeme Baldwin, BioMed Central May 28, 2009

Vancomycin resistant enterococci (VRE) have been found in sewage sludge, a by-product of waste-water treatment frequently used as a fertilizer. Researchers writing in the open access journal Acta Veterinaria Scandinavica point out the danger of antibiotic resistance genes passing into the human food chain.

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Leena Sahlström, from the Finnish Food safety Authority, worked with a team of researchers from the Swedish National Veterinary Institute to study sewage sludge from a waste-water treatment plant in Uppsala, Sweden. She said, “Antimicrobial resistance is a serious threat in veterinary medicine and human healthcare. Resistance genes can spread from animals, through the food-chain, and back to humans. Sewage sludge may act as one link in this chain”.

The researchers collected sludge from the plant every week for four months, for a total of 77 samples. Of these, 79% tested positive for the drug resistant superbugs. Although VRE themselves are not generally considered to be highly pathogenic, the danger is that they may pass on their resistance genes to other bacteria. Sahlström concludes, “Our results demonstrate a need for more efficient hygienic treatment of sewage sludge, in order to avoid possible spread of antimicrobial resistance through use of sewage sludge on arable land”.

Abstract: Vancomycin resistant enterococci (VRE) in Swedish sewage sludge

Acta Veterinaria Scandinavica 2009
Published: 29 May 2009

Background

Antimicrobial resistance is a serious threat in veterinary medicine and human healthcare. Resistance genes can spread from animals, through the food-chain, and back to humans. Sewage sludge may act as the link back from humans to animals. The main aims of this study were to investigate the occurrence of vancomycin resistant enterococci (VRE) in treated sewage sludge, in a Swedish waste water treatment plant (WWTP), and to compare VRE isolates from sewage sludge with isolates from humans and chickens. Methods

During a four month long study, sewage sludge was collected weekly and cultured for VRE. The VRE isolates from sewage sludge were analysed and compared to each other and to human and chicken VRE isolates by biochemical typing (PhenePlate), PFGE and antibiograms. Results

Biochemical typing (PhenePlate-FS) and pulsed field gel electrophoresis (PFGE) revealed prevalence of specific VRE strains in sewage sludge for up to 16 weeks. No connection was found between the VRE strains isolated from sludge, chickens and humans, indicating that human VRE did not originate from Swedish chicken. Conclusions

This study demonstrated widespread occurrence of VRE in sewage sludge in the studied WWTP. This implies a risk of antimicrobial resistance being spread to new farms and to the society via the environment if the sewage sludge is used on arable land.