Studies on the mode of action of phenylmercuric borate on Escherichia coli. II. Biochemical localization and inhibition of some metabolic activities.

The biochemical localization of phenylmercuric borate (PHB) on Escherichia coli shows that this disinfectant associates essentially with proteins. Protein electrophoresis demonstrates that each protein contains PHB, and that SH groups play a very important role in its fixation. The quantity of PHB able to associate with proteins is so large that many other electron donor groups must react with it. Moreover, it appears that concentration of PHB on cytoplasmic membrane results rather from the privileged position of this structure than from special physicochemical properties. The great reactivity of PHB towards proteins leads to numerous inhibitions and confers upon this antibacterial drug a very complex mode of action. Four important metabolic activities have been tested in the presence of PHB, namely: respiration, protein-synthesis, RNA synthesis and DNA synthesis. These four metabolic functions are rapidly and totally inhibited at low concentrations of PHB. The complexity of the mode of action of PHB makes the adaptation of bacteria to this disinfectant more difficult. In addition, in the case of plasmid dependent resistence, PHB, with its complexe mode of action, does not favour such a selection in opposition to the antibiotics which generally have a more specific mode of action.