Enhancement of antibacterial effect of quaternary ammonium with inorganic nanosheets against Enterobacter cloacae

To suppress nosocomial infections, numerous studies of quaternary ammonium cations (R4N+) to improve the antibiotic properties have been investigated. However, most of them reported developments of novel organic or polymeric materials with R4N+. To pioneer antibacterial inorganic materials hybridized with R4N+, a colloidal solution of metal oxide nanosheets, which have a small particle size (typically less than 10 nm), is considered to be a suitable option because oxide nanosheets with a negative surface charge strongly interact R4N+. Herein, we demonstrate for the first time that the high antibacterial/bactericidal effects of titanate nanosheets (TNS) adsorbing tetramethylammonium (TMA-TNS) or tetrabultylammonium ions (TBA-TNS). Their antibacterial effects against Enterobacter cloacae were evaluated using a colony forming unit (CFU) counting method. The results showed that the synthesized TNS composites had superior antibacterial and bactericidal effects to those of free R4N+ and TBA-TNS exhibited the strongest effect (69% CFU reduction compared with that of free TBA+ and 98% CFU reduction compared with the control) among the samples examined. Dark incubation was employed to ensure that photocatalytic reaction of semiconducting TNS did not contribute to the process. Compared with TiO2 spherical particles, such high bactericidal effect would be induced by a synergistic function of TBA+ and TNS, which physically damages bacteria due to long hydrophobic alkyl chains and an anisotropic nanocrystalline structure with sharp edges, respectively