The effect of single-walled carbon nanotubes on Escherichia coli: multiple indicators of viability

The impact of single-walled carbon nanotubes (SWCNTs) on Escherichia coli ATCC 8739 was investigated using four indicators of viability: enzyme activity, membrane integrity, plate count, and total RNA. The study examined the effects of SWCNT concentration (5, 10, 20, 50, 100, 200, 500, and 1,000 μg/ml), SWCNT length (0.5–2 and 5–30 μm), and bacterial density (6.5 log 10 CFU and 9 log 10 CFU per treatment) on E. coli ATCC 8739 viability. Results show that anti-bacterial activity is dependent on both the length and concentration of SWCNTs. Long SWCNTs (5–30 µm) were more toxic for E. coli than short SWCNTs (0.5–2 µm). The susceptibility of E. coli to SWCNTs was dependent on the initial density of cells in the treatment, with cells at the higher density being more resistant. Estimates of viability reductions were generally similar for the four assays examined; however, the beta galactosidase and LIVE/DEAD assays were more conservative than the plate count as indicators of viability reductions.