Fig 2.

Copper tolerance in N. gonorrhoeae. (A) Sensitivity of N. gonorrhoeae 1291 wild type (black bars) and 1291 copA (white bars) to zinc sulfate (Zn; 1 M), cadmium chloride (Cd; 10 mM), manganese sulfate (Mn; 100 mM), nickel sulfate (Ni; 50 mM), cobalt chloride (Co; 50 mM), iron nitrate (Fe; 1 M), and copper sulfate (Cu; 40 mM) (P = 0.005), as determined by disc diffusion assays. Error bars indicate ±1 standard deviation from the mean. (B) Effect of copper on the growth rate of N. gonorrhoeae 1291 (wild type), 1291 copA, and complemented 1291 copA. Wild-type and mutant gonococci were allowed to grow in liquid culture for 2 h (OD₆₀₀, ∼0.3), after which copper sulfate (denoted by arrows) was added to a final concentration of 0 mM (filled circles), 0.2 mM (empty circles), 0.4 mM (filled triangles), or 0.6 mM (empty triangles). These experiments were performed on at least three independent occasions, and representative growth curves are shown. (C) Survival of N. gonorrhoeae 1291 (wild type) (filled circles), 1291 copA (filled triangles), and complemented 1291 copA (empty circles) after 3 h of incubation with various defined concentrations of copper. CFU were determined by recovery of liquid cultures that had been challenged with copper sulfate as described in Materials and Methods. Experiments were performed on at least three independent occasions, and representative growth curves are shown. Error bars indicate ±1 standard deviation from the mean. (D) Intracellular copper content of N. gonorrhoeae 1291 (wild type) (filled circles), 1291 copA (filled triangles), and complemented 1291 copA (empty circles), as determined by ICP MS. Each horizontal line indicates the mean. P values were <0.0001 for all strains.