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Elucidating selection processes for antibiotic resistance in sewage treatment plants using metagenomics
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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2016 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 572, p. 697-712Article in journal (Refereed) Published
Abstract [en]

Sewage treatment plants (STPs) have repeatedly been suggested as “hotspots” for the emergence and dissemination of antibiotic-resistant bacteria. A critical question still unanswered is if selection pressures within STPs, caused by residual antibiotics or other co-selective agents, are sufficient to specifically promote resistance. To address this, we employed shotgun metagenomic sequencing of samples from different steps of the treatment process in three Swedish STPs. In parallel, concentrations of selected antibiotics, biocides and metals were analyzed. We found that concentrations of tetracycline and ciprofloxacin in the influent were above predicted concentrations for resistance selection, however, there was no consistent enrichment of resistance genes to any particular class of antibiotics in the STPs, neither for biocide and metal resistance genes. The most substantial change of the bacterial communities compared to human feces occurred already in the sewage pipes, manifested by a strong shift from obligate to facultative anaerobes. Through the treatment process, resistance genes against antibiotics, biocides and metals were not reduced to the same extent as fecal bacteria. The OXA-48 gene was consistently enriched in surplus and digested sludge. We find this worrying as OXA-48, still rare in Swedish clinical isolates, provides resistance to carbapenems, one of our most critically important classes of antibiotics. Taken together, metagenomics analyses did not provide clear support for specific antibiotic resistance selection. However, stronger selective forces affecting gross taxonomic composition, and with that resistance gene abundances, limit interpretability. Comprehensive analyses of resistant/non-resistant strains within relevant species are therefore warranted.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 572, p. 697-712
Keywords [en]
Antibiotic resistance genes, Co-selection, Fecal bacteria, Microbial ecology, Risk assessment, Wastewater treatment
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-128824DOI: 10.1016/j.scitotenv.2016.06.228ISI: 000387807200068PubMedID: 27542633OAI: oai:DiVA.org:umu-128824DiVA, id: diva2:1056754
Available from: 2016-12-15 Created: 2016-12-15 Last updated: 2018-10-11Bibliographically approved
In thesis
1. Antimicrobials in sewage treatment plants: occurrence, fate and resistance
Open this publication in new window or tab >>Antimicrobials in sewage treatment plants: occurrence, fate and resistance
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Antimikrobiella ämnen i avloppsreningsverk : förekomst, avskiljning och resistens
Abstract [en]

The World Health Organization (WHO) has identified antibiotic resistance as a major threat to human health. The environment has been suggested to play an important role in the emergence of antibiotic resistant bacteria. The external environment can act as a source of resistance genes that could potentially be transferred into human pathogens. It is also an important route for the dissemination of antibiotic resistance genes and bacteria. Sewage treatment plants (STPs) are among the most important routes by which antibiotics and antibiotic resistance genes enter the environment. It has been suggested that STPs are hotspots for the development of antibiotic resistance because they contain relatively high concentrations of antibiotics as well as both human and environmental bacteria. Further complicating matters, there is evidence that other substances with antimicrobial properties, such as biocides and metals, can cause antibiotic resistance due to co- and cross-resistance.

This thesis contributes new knowledge on the concentrations, mass flows, and removal efficiencies of antimicrobials in STPs and their connections to the emergence of antibiotic resistance. Paper I presents data on the levels of 40 different antimicrobials in the incoming wastewater, treated effluent, and digested sludge of eleven different STPs. Although not previously detected in STPs, chlorhexidine is shown to be ubiquitous in such plants. In Paper II, mass flows and removal efficiencies are calculated for eleven antimicrobials over various treatment steps in three STPs, showing that polar antimicrobials were inefficiently removed from the wastewater. In Paper III, the minimum selective concentration (MSC) for the antibiotic tetracycline was determined in a complex bacterial aquatic biofilm using both phenotypic and genotypic endpoints. It was found that 10 µg/L selected for phenotypic resistance, and 1 µg/L selected for certain resistance genes. Paper VI used metagenomics to determine whether there is selection for antibiotic-resistant bacteria in STPs and whether the extent of this selection can be correlated to the concentrations of antimicrobial compounds. No clear evidence for selection was identified. Paper V evaluates advanced wastewater treatment techniques for removing antimicrobial compounds using ozonation and granular activated carbon (GAC). The identity of the GAC material was found to strongly affect removal efficiency, and GAC was more efficient than ozonation for most compounds at the tested concentrations.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2018. p. 77
Keywords
biocides, antibiotics, sewage treatment plants, wastewater, sludge, ozonation, activated carbon, antibiotic resistance, antimicrobials, mass flows, LC-MS/MS, environment, advanced water treatment
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:umu:diva-152554 (URN)978-91-7601-938-2 (ISBN)
Public defence
2018-11-07, Aula Anatomica (Bio.A.206), Biologihuset, Umeå, 13:00 (English)
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Available from: 2018-10-17 Created: 2018-10-11 Last updated: 2018-10-15Bibliographically approved

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Östman, MarcusFick, JerkerTysklind, Mats

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