Elucidating selection processes for antibiotic resistance in sewage treatment plants using metagenomics
Artikel i vetenskaplig tidskrift, 2016

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.

Microbial ecology

Wastewater treatment

Risk assessment

Fecal bacteria

Antibiotic resistance genes



Johan Bengtsson-Palme

Göteborgs universitet

Rickard Hammarén

Göteborgs universitet

C. Pal

Göteborgs universitet

M. Ostman

Umea universitet

Berndt Björlenius

The Royal Institute of Technology (KTH)

Carl-Fredrik Flach

Göteborgs universitet

Erik Kristiansson

Göteborgs universitet

Chalmers, Matematiska vetenskaper, matematisk statistik

Jerker Fick

Chalmers University of Technology

Centre for Antibiotic Resistance Research (CARe) at University of Gothenburg

M. Tysklind

Umea universitet

D. G. Joakim Larsson

Göteborgs universitet

Science of the Total Environment

0048-9697 (ISSN)

Vol. 572 697-712