Graveyard effects of antimicrobial nanostructured titanium over prolonged exposure to drug resistant bacteria and fungi

Innovations in nanostructured surfaces have found a practical place in the medical area with use in implant materials for post-operative infection prevention. These textured surfaces should be dual purpose: (1) bactericidal on contact and (2) resistant to biofilm formation over prolonged periods. Here, hydrothermally etched titanium surfaces were tested against two highly antimicrobial resistant microbial species, methicillin-resistant <i>Staphylococcus aureus</i> and <i>Candida albicans</i>. Two surface types - unmodified titanium and nanostructured titanium - were incubated in a suspension of each microbial strain for 1 day and 7 days. Surface topography and cross-sectional information of the microbial cells adhered to the surfaces, along with biomass volume and live/dead rate, showed that while nanostructured titanium was able to kill microbes after 1 day of exposure, after 7 days, the rate of death becomes negligible when compared to the unmodified titanium. This suggests that as biofilms mature on a nanostructured surface, the cells that have lysed conceal the nanostructures and prime the surface for planktonic cells to adhere, decreasing the possibility of structure-induced lysis. Synchrotron macro-attenuated total reflection Fourier transform infrared (macro ATR-FTIR) micro-spectroscopy was used to elucidate the biochemical changes occurring following exposure to differing surface texture and incubation duration, providing further understanding into the effects of surface morphology on the biochemical molecules (lipids, proteins and polysaccharides) in an evolving and growing microbial colony.