Spatial correlation between antibiotic resistance and heavy metal concentration in contaminated streams.
Tuckfield, R. Cary1, McArthur, J Vaun2, 1 Savannah River Technology Center, Aiken, SC, USA2 Savanah River Ecology Labortory, Aiken, SC, 29808
ABSTRACT- Heavy metal tolerance among aquatic bacteria is often associated with the presence of antibiotic resistance among the same microbes in the same environments. However, no study has explored the spatial relationship between antibiotic resistance and point sources of metal contamination upstream. We collected 151 sediment samples sequentially downstream-to-upstream from three streams at the Savannah River Site, two metals contaminated (FMC and CC) and one uncontaminated (MB), and an additional 14 samples from a fourth (contaminated) stream in a mine drainage in northern Washington state (LC). Sample extracts were growth plated in triplicate - control and two antibiotic (kanamycin and streptomycin) treatments - and bacterial colonies counted after 6 days. The concentrations for 10 heavy metals were also measured for each sediment sample. Principal component scores were generated separately for the antibiotic and metal variables. Opposite spatial patterns with downstream distance were found between the antibiotic resistance principal component scores and metal component scores in FMC, CC, and LC. That is, these two principal components were negatively correlated (p < .05). No such pattern exists in MB. In addition, the geostatistical methods of variography and cross-variography showed a diminishing positive spatial correlation for antibiotic resistance principal component scores or for metal component scores with increasing separation distance between samples in FMC, CC, and LC but not MB. Similarly, we demonstrate a diminishing negative spatial cross-correlation between these two components for the contaminated streams but not the uncontaminated stream. These results, although apparently consistent among contaminated streams, run counter to the hypothesis underlying our research, namely that direct selection for heavy metal tolerance may also indirectly select environmental bacteria for antibiotic resistance via a mechanism such as genetic linkage.
Key words: spatial correlation, antibiotic resistance, variography, metal tolerance
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