Cobalt and nickel sensitivity and tolerance in Klebsiella pneumoniae.

In liquid medium the lag of K. pneumoniae NCIB 418 increased progressively as the Co2+ or Ni2+ concentration was increased, and Ni2+ was more inhibitory than Co2+. Adding EDTA, citrate or aspartate, removed this action, and changing to conditions of K+-limitation reduced it significantly but Mg2+-limited organisms were more sensitive to both metal ions. Resistence to Co2+ and Ni2+ developed. It was graded to the concentration to which the organisms were previously exposed and reciprocal cross-resistance, albeit partial, occurred between the ions. On agar-media the concentrations of Co2+ and Ni2+, which reduced the survival to 50%, were not significantly different and in admixture the ions exerted an additive effect. On the other hand the combination of either of the metal ions with Cd2+ or Zeciprocal cross-resistance, albeit partial, occurred between the ions. On agar-media the concentrations of Co2+ and Ni2+, which reduced the survival to 50%, were not significantly different and in admixture the ions exerted an additive effect. On the other hand the combination of either of the metal ions with Cd2+ or Zeciprocal cross-resistance, albeit partial, occurred between the ions. On agar-media the concentrations of Co2+ and Ni2+, which reduced the survival to 50%, were not significantly different and in admixture the ions exerted an additive effect. On the other hand the combination of either of the metal ions with Cd2+ or Zn2+, especially with Cd2+, was synergistic. The results are discussed with reference to the work of others with Co2+ and Ni2+, and to our earlier work with Cd2+, Cu2+, Zn2+, Tl+ and crO42-.