The present invention relates to a water-resistant organic thin film obtained by crosslinking, with organic nitrogen compounds, an organic thin film comprising an organic dye having an anionic group, wherein the organic nitrogen compounds are first, second, and third acyclic organic nitrogen compounds each having two or more nitrogen atoms per molecule, wherein the nitrogen atoms of each of the first, second, and third organic nitrogen compounds are each in a cationic group, and the relation A0.4 nm<B<C is satisfied, wherein A represents a distance (nm) between adjacent nitrogen atoms in the first organic nitrogen compound, B represents a distance (nm) between adjacent nitrogen atoms in the second organic nitrogen compound, and C represents a distance (nm) between adjacent nitrogen atoms in the third organic nitrogen compound.

Provided herein are methods for inducing cell death in a gram positive bacterium and methods for reducing the proliferation of a gram positive bacterium that include contacting a gram positive bacterium with a dye (e.g., an azo dye) and a TarO inhibitor. Also provided are methods of treating a subject having a gram positive bacterial infection that include administering to a subject having a gram positive bacterial infection a dye (e.g., an azo dye) and a TarO inhibitor. Also provided are compositions containing a dye (e.g., an azo dye) and a TarO inhibitor, and kits containing at least one of these compositions.