TEM Observation of Cells Treated with Metal Ions

<p>Copper, Silver, Nikel and Zinc are well known as antibacterial metal. Introducing antibacterial metals into environment surface in hospitals will decrease the number of viable bacteria on the surface of medical instruments and foods making appliances. On the other hand,the antibacterial(killing) mechanism of antibacterial metals has not yet been fully described. A couple of explanations have been proposed. (1) Reactiv oxygen species are generated from the metal surface. (2) Hydrogen peroxide is caused by Fenton–type reactions. (3) Metal ion combines with bacterial cell components. But how to change of bacterial cell structure by killing action come about is not known yet.</p><p>In this investigation , imaging of cell structures damaged by metal ion is attempted. Bacterial cells were treated with an antibacterial metal ion solution. Treating times were varied from 2 hour to 12 hour. The treated cells were collected by centrifugation, chemically fixed, and embedded in resin. Ultra–thin sections were cut from them and observed by transmission electron microscope. Precipitates in damaged cell were analyzed by EDX. In this investigation , as first trials, Ag was selected.Ag has the most strong killing effect compared with Cu ,Ni, and Zn. Ag ion content of the solution was 5ppm.</p><p>Staphylococcus aureus was tested. The antibacterial property was evaluated in accordance with JIS Z 2801. The structure of Staphylococcus aureus sustained increasing damage with the lapse of time. After at least 4 hour, small particles of precipitate in the damaged cells were found. From the precipitates, Ag and S were detected by EDX analysis. It appears that Ag ion diffuses into cell and combine with cell components.</p><p>Consequently, an activities of Staphylococcus aureus are dramatically decreased. Also, cell wall thickness decreased with exposure time. From the obtained results, the possible killing mechanisms are discussed. Finally, this study concludes that TEM observation is a useful a tool for this type of investigation.</p>