Bronopol

It is proposed that bronopol generates biocide-induced bacteriostasis followed by a growth at an inhibited rate in bacteria, via two distinct reactions between bronopol and essential thiols within the bacterial cell. Under aerobic conditions, bronopol catalyzes the oxidation of thiol groups, such as cysteine, to disulfides. This reaction is accompanied by rapid consumption of oxygen, where oxygen acts as the final oxidant. During the conversion of cysteine to cystine, radical anion intermediates such as superoxide and peroxide are formed from bronopol to exert a direct bactericidal activity. The oxidation of excess thiols alters the redox state to create anoxic conditions, leading to a second reaction involving the oxidation of intracellular thiols such as glutathione to its disulfide. The resulting effects are inhibition of enzyme function, and reduced growth rate following the bacteriostatic period. Under the anoxic conditions, the reaction between thiol and bronopol decelerates without the involvement of oxygen and the consumption of bronopol predominates. Bronopol is ultimately removed from the reaction via consumption and resumption of bacterial growth occurs.