Bowen Li1, Susan T. Bagley2, and Jiann-Yang Hwang1. (1) Materials Science & Engineering, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931-1295, (2) Biological Sciences, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931-1295
Copper vermiculite (Cu-V) is new type of synthetic antimicrobial agent having potential as a functional additive in products such as plastics, paints, leathers, and woods to reduce microbial persistence and biofilm formation. The antibacterial efficiency of Cu-V was evaluated by determining its minimum inhibitory concentration (MIC) against Escherichia coli along with the stability of the Cu-V. The crude vermiculite was a concentrate that was jet-milled to μm-sized powder (mean particle size of 2.06 μm and 99% of particles <5.13 μm). The Cu-V was prepared by cation exchange reaction at 80°C; the resulting atomic content of copper (as Cu2+) was 2.55 wt%. Based on field emission scanning electron microscopy, the Cu atoms were homogeneously dispersed in the vermiculite structure. Overnight (12 – 18h at 37°C) E. coli suspensions of 1~2×107 CFU/ml were used. Copper levels of 0.255 to 5.10 ppm (10 ppm to 200 ppm Cu-V) were examined with all experiments repeated three times. In the control vermiculite suspensions, E. coli densities remained constant during the 12 hour contact time; in contrast, bacteria levels with Cu-V significantly decreased. In the experiment with 200 ppm Cu-V (5.10 ppm Cu), viable E. coli levels were reduced by 94.8% at 1 hour, 99.6% at 2 hours, and >99.9% at 4 hours. The Cu-V MIC level against E. coli was10 ppm, while the untreated vermiculite had no antibacterial activity. Very little Cu was detected in the growth medium during the study, indicating that the Cu-V’s antimicrobial effect was due to surface interactions.
