Figure 6.

Proposed mechanism of action of ZnPor against PsA biofilms and individual cells. (A.I) The top panel represents a 16–18 h biofilm imaged after treatment with the LIVE/DEAD stain (as shown in Figure 2C control): a thick layer of cells encased in an extracellular matrix (ECM). All or almost all stained green with the LIVE/DEAD stain. The ECM contains a variety of different biomolecules, e.g., eDNA, which constitutes the majority of the ECM. ZnPor can diffuse throughout the ECM (as shown in Figure 2A) and thus interact with the eDNA in the matrix. (A.II) ZnPor treatment (prior to LIVE/DEAD) had the effect of destabilizing the biofilm, and ultimately, the biofilm sloughed off the surface (II,III). LIVE/DEAD-stained biofilms depict dead biofilm-associated cells left on the surface after ZnPor treatment. Overall, the matrices of biofilms treated with ZnPor were converted from thick and dense matrices to thin monolayers of almost exclusively dead cells, and the biofilms detached from the surfaces. (B) Individual planktonic PsA cells rapidly accumulated ZnPor in the cytoplasm and membrane/cell wall (Figure 3A). We hypothesize that ZnPor in the cytoplasm binds to the chromosomal DNA and inhibits replication. As shown in Figure 4A, ZnPor-treated cells did not increase in total number (nor did they decrease); these cells did not form colonies when plated onto LB agar plates and thus were not viable (Figure 4B). However, the cells did not lyse, as indicated in Figure 4C.