Analysis of bacterial growth at various distances from an antimicrobial surface

Antimicrobial materials have been used in various environments. However, the activity of cells at a distance from the antimicrobial materials has not been elucidated. In the present study, the cell growth of Escherichia coli NBRC 3972 was observed at different distances (0 - 300 μm) from the antimicrobial surface under various nutrient concentrations, from full strength nutrient broth (NB) to 1/40 NB. Under higher nutrient concentrations, NB and 1/2 NB, no antimicrobial effect on cell growth was observed at any distance from the surface. Under lower nutrient concentrations, 1/10 NB and 1/40 NB, the growth of cells directly contacting the antimicrobial surface (at 0 μm from the surface) was blocked immediately after inoculation on the surface. However, at distances of 100 - 300 μm from the surface, the cells grew normally for a while, and then stopped the growth; earlier growth discontinuation was observed for cells closer to the surface. It was suggested that the antimicrobial agent (silver ions) is released from the antimicrobial surface into the medium and that the diffusion of the silver ions may influence the lag in the antimicrobial effects observed at distances away from the antimicrobial surface. The present study reveals the possibility that antimicrobial activity in the environments where the antimicrobial material is used depends on the distance from the surface and the surrounding nutrient concentrations.