TCDD influences reservoir of antibiotic resistance genes in murine gut microbiome

Abstract

One sentence summary: An environmental toxicant that is not a metal, biocide or antimicrobial indirectly (via a non-inflammatory host response) influences the reservoir of antibiotic resistance genes in the murine gut. Editor: Kornelia Smalla ABSTRACTDysbiosis of the gut microbiome via antibiotics, changes in diet and infection can select for bacterial groups that more frequently harbor antimicrobial resistance genes (ARGs) and mobile genetic elements (MGEs). However, the impact of environmental toxicants on the reservoir of ARGs in the gut microbiome has received less attention. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent aryl hydrocarbon receptor (AhR) agonist with multiple toxic health effects including immune dysfunction. The selective pressure of TCDD on the abundance of ARG and MGE-harboring gut populations was examined using C57BL/6 mice exposed to 0-30 μg/kg TCDD for 28 and 92 days with the latter having a 30-day recovery period. DNA extracted from temporally collected fecal pellets was characterized using a qPCR array with 384 assays targeting ARGs and MGEs. Fourteen genes, typically observed in Enterobacteriaceae, increased significantly within 8 days of initial dosing, persisted throughout the treatment period, and remained induced 30 days post dosing. A qPCR primer set targeting Enterobacteriaceae also showed 10-to 100-fold higher abundance in TCDD-treated groups, which was further verified using metagenomics. Results show a bloom of ARG-harboring bacterial groups in the gut due to a xenobiotic compound that is not a metal, biocide or antimicrobial.

TCDD administered on activated carbon eliminates bioavailability and subsequent shifts to a key murine gut commensal

“…In detail, only three bacterial families including Methanosaetaceae , Erysipelotrichaceae , and a group from clostridia were significantly reduced ( p < 0.05) in mice dosed with CO. In our previous studies using sesame oil—a common vehicle (Brown et al 1998; Kopec et al 2008), we observed a response that opposed TCDD in terms of shifting SFB, Firmicutes , and Enterobacteriaceae (Bhaduri 2015; Stedtfeld et al 2017, submitted). For example, compared to the relative abundance 1 day before dosing, Enterobacteriaceae in fecal pellets decreased ~ 10-fold and 300-fold, 3 and 7 days following an initial dose of sesame oil, respectively.…”

“…SFB was selected as a marker because it interacts with host immunity (Ivanov et al 2009) and responds to TCDD in the murine model (Stedtfeld et al 2017; Bhaduri 2015). Previous studies have surmised that shift in the gut microbiome, including SFB, is an indirect response to TCDD-induced modulation of the immune system (Zhang et al 2015; Lefever et al 2016; Stedtfeld et al 2017).…”

“…This is an important question as the gut microbiota plays a crucial role in host health and immune competence (Littman and Pamer 2011; Honda and Littman 2016). Previous studies have observed TCDD-induced dysbiosis of gut commensals including Candidatus Savagella also known as segmented filamentous bacteria (SFB), Firmicutes , and Enterobacteriaceae (Bhaduri 2015; Lefever et al 2016; Stedtfeld et al 2017, Modulatory influence of segmented filamentous bacteria on transcriptomic response of gnotobiotic mice exposed to TCDD, submitted). Experiments performed by our group and others suggest that gut commensal response is the result of TCDD-induced toxicity to the host, mediated in part, through the aryl hydrocarbon receptor (AhR), and not the direct influence of TCDD on bacteria (Lefever et al 2016; Stedtfeld et al 2017).…”

“…Previous studies have observed TCDD-induced dysbiosis of gut commensals including Candidatus Savagella also known as segmented filamentous bacteria (SFB), Firmicutes , and Enterobacteriaceae (Bhaduri 2015; Lefever et al 2016; Stedtfeld et al 2017, Modulatory influence of segmented filamentous bacteria on transcriptomic response of gnotobiotic mice exposed to TCDD, submitted). Experiments performed by our group and others suggest that gut commensal response is the result of TCDD-induced toxicity to the host, mediated in part, through the aryl hydrocarbon receptor (AhR), and not the direct influence of TCDD on bacteria (Lefever et al 2016; Stedtfeld et al 2017). Given the recently demonstrated limited bioavailability of AC-TCDD to hallmark responses in mice (Boyd et al 2017), we hypothesized that the response of key gut commensals would also be muted.…”

“…Given the recently demonstrated limited bioavailability of AC-TCDD to hallmark responses in mice (Boyd et al 2017), we hypothesized that the response of key gut commensals would also be muted. To test this hypothesis, the transcriptomic response of SFB was examined, which has previously been shown to respond to the toxicity induced by TCDD (Bhaduri 2015; Stedtfeld et al 2017) and other AhR ligands (Zhang et al 2015). …”