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.
Root tips were soaked 1-2 hours at 18-20" C. in a freshly prepared saturated aqueous solution of a-bromonaphthalene, 1-2 hours in water, and fixed in a mixture consisting of 1% chromic acid, 5 ml.; 2% osmic acid, 1 ml.; and 0.002 M 8-0xyquinoline, 1 ml. for 0.5-1.0 hour at 10-14" C. They were then successively treated as follows: water 1-2 minutes; 1% H,SO,, 10-15 minutes; water, 1-2 minutes; 1% Cr03, 0.5-1.0 hour; water 3-5 minutes; 1 N HCl, 45 minutes at 60" C.; water 3-5 minutes; leucobasic fuchsin (de Tomasi) 0.5-1.0 hour. The brightly stained tips of the roots were cut off and squashed in the usual manner in a drop of aceto-carmine under a cover glass. The cover glass was sealed with paraffin and the slide stored overnight. T h e paraffin was removed and the cover glass separated in a -l : l mixture of acetic acid and n-butyl alcohol. Final processing consisted of passing the slide through pure n-butyl alcohol; a 1:l mixture of redistilled turpentine and n-butyl alcohol (to remove-the osmic acid stain); n-butyl alcohol, 2 changes, and covering in balsam.
:A review of the literature published in 2008 is presented on topics related to occurrence and detection of fecal indicators and pathogens. This review is divided into three major sections: occurrence, persistence, and transport of fecal indicators and pathogens, detection methods, and microbial source tracking. The first section is subdivided into persistence and transport of fecal indicators, microbiological quality of recreational beaches, occurrence of fecal indicator and pathogens in shellfish, alternative fecal indicators, and fecal indicators and pathogens in groundwater, watersheds, and wetlands. The second section describes the studies related to endpoint PCR and reverse transcription PCR, real‐time PCR and real‐time reverse transcription PCR, loop mediated isothermal amplification, microarrays, immunoassay‐based detection schemes, labelindependent detection schemes, and sample concentration. The third section covers genotypic and phenotypic microbial source tracking methods.
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