Antibiotic resistance genes in sewage sludge submitted to anaerobic digestion
Résumé
Anaerobic digestion (AD) can be applied to optimize the treatment and recycling of sewage sludge. However, owing to its origin, sewage sludge may be rich in antibiotic residues and antibiotic resistance genes (ARG), possibly persisting in the digestate, produced during AD. It has been demonstrated that two other processes, composting and drying, significantly reduced the relative abundance of ARG as well as mobile genetic element genes (MGEG) in organic waste. We hypothesize that a similar reduction of ARG may occur during AD. The goal of the current study was to survey the amounts of ARG and MGEG in sewage sludge during AD. Dry batch co-digestion of manure and sludge was studied in pilot reactors (5 weeks, 37°C). Relevant physico-chemical parameters like biogas production were monitored. Copy numbers of 380 ARG and MGEG were determined from the DNA extracted from the digestate, using high throughput quantitative PCR (SmartChip System, Takara). Fifty-six genes could be detected corresponding to 10 MGEG, 13 amino-glycosides, 9 tetracycline, 8 Macrolide-lincosamide-streptogramine, 5 beta lactams, 2 sulfonamide, one phenicol, one trimethoprim, one fluoroquinolone and 5 multi drug resistance genes. Four of the most abundant genes were from Macrolide-lincosamide-streptogramine (notably erm gene). The hypothesized diminution of ARG during anaerobic digestion was not revealed.
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