Figure 1.

Antibacterial effect of ZnPor on planktonic Pseudomonas aeruginosa (PsA). (A.I.) and (A.II.) show minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of ZnPor: Overnight PsA cultures were diluted to 10⁴ cells/mL. Mueller–Hilton broth was used as the testing medium as per Clinical and Laboratory Standard Institute (CLSI) guidelines, and minimum salts with 0.4% glucose were used as the testing medium for this study. (A) series of 2-fold dilutions of ZnPor was used to achieve concentrations in the wells from 0.5 to 16 µg/mL. (I) shows the reduction of the dye resazurin by live cells, from purple to pink. The lowest concentration (MIC) at which no growth was seen compared to control was indicated by the purple color. (A.II) represents viable plate counts of cell suspensions in the wells shown in (A.I.) MIC and the next two higher concentrations were plated on Luria Bertani (LB) to determine MBC. An MBC/MIC ratio <4 is considered a sign that an organism is susceptible to an antimicrobial. Additionally, we have yet to isolate any resistant variants. (B) Time–kill curve of planktonic PsA treated with ZnPor. Overnight PsA cultures were diluted to 10⁴ cells/mL in minimal salts and glucose (MSG) medium, and ZnPor was added at concentrations from 1 to 8 µg/mL. Controls received no ZnPor. Viable plate counts (CFU/mL) were determined by plating samples on LB agar at the time points shown. (C) Combinatory effect of Tobra and ZnPor on PsA planktonic cells. MIC of Tobra was compared to Tobra+ZnPor using the checkerboard micro-broth dilution method. All data points represent mean ± SD of three independent experiments (n = 9), with 3 samples per time point. * p-value < 0.005; ** no bacterial growth.