Twenty-nine bacterial isolates representing eight genera from the gastrointestinal tracts of feral brook trout Salvelinus fontinalis (Mitchell) demonstrated multiple maximal antibiotic resistances and concomitant broad-spectrum mercury (Hg) resistance. Equivalent viable plate counts on tryptic soy agar supplemented with either 0 or 25 μM HgCl2 verified the ubiquity of mercury resistance in this microbial environment. Mercury levels in lake water samples measured 1.5 ng L-1; mercury concentrations in fish filets ranged from 81.8 to 1,080 ng g-1 and correlated with fish length. The presence of similar antibiotic and Hg resistance patterns in multiple genera of gastrointestinal microflora supports a growing body of research that multiple selective genes can be transferred horizontally in the presence of an unrelated individual selective pressure.We present data that bioaccumulation of non-point source Hg pollution could be a selective pressure to accumulate both antibiotic and Hg resistant bacteria.
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The authors would like to acknowledge Drs. A.O. Summers (University of Georgia, Athens, GA, USA), and G.M. King (Louisiana State University, Baton Rouge, LA, USA), for helpful advice and assistance in experimental design. The project was supported at Colby College by grants from the National Center for Research Resources (5P20RR016463-12) and the National Institute of General Medical Sciences (8 P20 GM103423-12) from the National Institutes of Health, Colby College Student Special Projects Fund, Colby College Natural Science Division Grant (#01.2375, F.A. Fekete), the Maine Department of Inland Fisheries & Wildlife, by the Department of Biology and the Office of Teaching and Faculty Development at Bradley University (K.A. Johnson), and by the National Science Foundation through a Research Experiences for Undergraduates supplement to EAR-0525374 (T. Barkay).