Enrichment of cadmium-mediated antibiotic-resistant bacteria in a Douglas fir (Pseudotsuga menziesii) litter microcosm

Abstract

A set of Douglas-fir needle litter microcosms was amended with cadmium, acid, a combination of both, or neither. After 2 weeks of incubation, bacterial colony counts were made of litter homogenates inoculated onto agar media containing an antibiotic (streptomycin, chloromycetin, ampicillin, or gentamicin), cadmium, both, or neither. In all microcosms bacterial abundance was similar but the quality was very dissimilar. Cadmium-treated microcosms had populations enriched for cadmium and gentamicin resitance and streptomycin and chloramphenicol sensitivity. Acid amendment had no consistent effect on the microcosm populations except that which could be attributed to the cadmium treatment amendment alone.