Fate of antibiotic resistant E. coli and antibiotic resistance genes during full scale conventional and advanced anaerobic digestion of sewage sludge

Abstract

Antibiotic resistant bacteria (ARB) and their genes (ARGs) have become recognised as significant emerging environmental pollutants. ARB and ARGs in sewage sludge can be transmitted back to humans via the food chain when sludge is recycled to agricultural land, making sludge treatment key to control the release of ARB and ARGs to the environment. This study investigated the fate of antibiotic resistant Escherichia coli and a large set of antibiotic resistance genes (ARGs) during full scale anaerobic digestion (AD) of sewage sludge at two U.K. wastewater treatment plants and evaluated the impact of thermal hydrolysis (TH) pre-treatment on their abundance and diversity. Absolute abundance of 13 ARGs and the Class I integron gene intI1 was calculated using single gene quantitative (q) PCR. High through-put qPCR analysis was also used to determine the relative abundance of 370 ARGs and mobile genetic elements (MGEs). Results revealed that TH reduced the absolute abundance of all ARGs tested and intI1 by 10–12,000 fold. After subsequent AD, a rebound effect was seen in many ARGs. The fate of ARGs during AD without pre-treatment was variable. Relative abundance of most ARGs and MGEs decreased or fluctuated, with the exception of macrolide resistance genes, which were enriched at both plants, and tetracyline and glycopeptide resistance genes which were enriched in the plant employing TH. Diversity of ARGs and MGEs decreased in both plants during sludge treatment. Principal coordinates analysis revealed that ARGs are clearly distinguished according to treatment step, whereas MGEs in digested sludge cluster according to site. This study provides a comprehensive within-digestor analysis of the fate of ARGs, MGEs and antibiotic resistant E. coli and highlights the effectiveness of AD, particularly when TH is used as a pre-treatment, at reducing the abundance of most ARGs and MGEs in sludgeand preventing their release into the environment.

Bench-Scale Liquid-Phase Microaeration and Iron Dosing Comparison for In Situ Biogas Desulfurization and Antibiotic Resistance Management in Mesophilic Anaerobic Digestion

“…It is worth noting that the abundance of various ARGs was within the range of absolute abundance of ARGs about 10 4 to 10 10 copies per gram of sludge reported for digestate from full-scale sludge mesophilic AD in the literature. 52,53 Overall, the total copies of ARGs for the microaeration and iron-dosed reactors were 8.8 × 10 4 and 9.1 × 10 4 per gram of sludge which was significantly lower (p-value = <0.001) than the control (1.2 × 10 5 gene copies/g sludge) (Figure 5). Analogous to ARGs, MGEs (intl1 and intl2) also showed similar patterns, i.e., substantially higher levels (p-value = <0.001) in the control than in test reactors.…”

Effect of Wastewater Treatment on Bacterial Community, Antibiotic-Resistant Bacteria and Endoparasites

“…In untreated sludge, Redhead et al [ 72 ] found higher resistance of E. coli isolates to amoxicillin, trimethoprim, ciprofloxacin, and gentamicin. After thermal hydrolysis at WWTPs, the absolute abundance was markedly reduced in dfrA1 , dfrA5 , dfrA7 , aac(3)-1 , CTX-M-1, CTX-M-9, bla-Imp , qnrS , tetM , sul1 , and intl1 genes, which is similar to the data observed by Martins et al [ 73 ] and Raven et al [ 74 ].…”

Long-Term, Simultaneous Impact of Antimicrobials on the Efficiency of Anaerobic Digestion of Sewage Sludge and Changes in the Microbial Community

“…The impact of antimicrobials on anaerobic digestion [27,28] and the elimination of ARGs during methane fermentation [29,30] have been explored by many researchers. These problems were also addressed in our previous research [5,31].…”