Effect of Various Sludge Digestion Conditions on Sulfonamide, Macrolide, and Tetracycline Resistance Genes and Class I Integrons

Abstract

Wastewater treatment processes are of growing interest as a potential means to limit the dissemination of antibiotic resistance. This study examines the response of nine representative antibiotic resistance genes (ARGs) encoding resistance to sulfonamide (sulI, sulII), erythromycin (erm(B), erm(F)), and tetracycline (tet(O), tet(W), tet(C), tet(G), tet(X)) to various laboratory-scale sludge digestion processes. The class I integron gene (intI1) was also monitored as an indicator of horizontal gene transfer potential and multiple antibiotic resistance. Mesophilic anaerobic digestion at both 10 and 20 day solids retention times (SRTs) significantly reduced sulI, suII, tet(C), tet(G), and tet(X) with longer SRT exhibiting a greater extent of removal; however, tet(W), erm(B) and erm(F) genes increased relative to the feed. Thermophilic anaerobic digesters operating at 47 °C, 52 °C, and 59 °C performed similarly to each other and provided more effective reduction of erm(B), erm(F), tet(O), and tet(W) compared to mesophilic digestion. However, thermophilic digestion resulted in similar or poorer removal of all other ARGs and intI1. Thermal hydrolysis pretreatment drastically reduced all ARGs, but they generally rebounded during subsequent anaerobic and aerobic digestion treatments. To gain insight into potential mechanisms driving ARG behavior in the digesters, the dominant bacterial communities were compared by denaturing gradient gel electrophoresis. The overall results suggest that bacterial community composition of the sludge digestion process, as controlled by the physical operating characteristics, drives the distribution of ARGs present in the produced biosolids, more so than the influent ARG composition.

Effects of electron acceptors on removal of antibiotic resistant Escherichia coli, resistance genes and class 1 integrons under anaerobic conditions

“…2). The BES anode essentially functioned as an anaerobic digester under the open circuit condition, but the log removal of ARGs achieved (ranging from 2.16 to 3.19 log reduction) here was higher than that reported for mesophilic and thermophilic anaerobic digesters (Ma et al, 2011). This higher removal could be related to the highly specific environment (acetate as the sole carbon source) and limited electron acceptors in the BES anode (no electron acceptors were added in the substrate).…”

“…The culture isolated with HiCrome™ m-TEC agar was confirmed to be E. coli by detecting the E. coli specific gene uidA (Maheux et al, 2009). A series of PCR assays served to detect ARGs (Ma et al, 2011). The presence of sulI, tet(E) and intI1 was confirmed to be of the expected size using gel electrophoresis (SI Fig.…”

“…Quantitative PCR was performed on a Real Time PCR System (7300, Applied Biosystems, CA, USA) with SsoFast Evagreen Supermix (Bio-Rad Laboratories, CA, USA) to quantify bacterial 16S rRNA gene, uidA, intI1 and sulI, tet(E). The qPCR protocols have been validated and reported in a previous study (Ma et al, 2011). A dilution series was performed and 1:20 was selected and applied across DNA extracts to minimize inhibitory effects.…”

“…It has been reported that a two-stage thermophilic/ mesophilic anaerobic digestion system can efficiently remove ARGs associated with tetracycline resistance (Ghosh et al, 2009). In another study, both the mesophilic and thermophilic anaerobic digesters showed approximately 1 log removal of nine ARGs, while a longer solids retention time and elevated temperature were suspected to play an important role in their fate (Ma et al, 2011). The removal rate and efficiency of ARGs encoding tetracycline resistance could be increased with increased temperature of the digester (Diehl and LaPara, 2010).…”

Antibiotic resistance genes in manure-amended soil and vegetables at harvest

“…In this study, it was found that intI1 gene had significantly positive correlation with sulI, sulII, tetA, tetC, tetG, and tetBP genes, indicating that intI1 gene may play certain role in the dissemination of ARGs. Previous study have demonstrated that integrons can be used by Gram-positive and Gram-negative bacteria to stockpile and express different exogenous resistance genes and are considered to play a central role in the worldwide problem of antibiotic resistance [39][40][41]. Partridge et al found that sulI gene was carried within the 3 conserved region of class 1 integron, and such an association may facilitate and enhance its persistence [42].…”