L­histidine augments the oxidative damage against Gram­negative bacteria by hydrogen peroxide.

Excessive damage to DNA and lipid membranes by reactive oxygen species reduces the viability of bacteria. In the present study, the proliferation of recA­deficient Escherichia coli strains was revealed to be inhibited by 1% L­histidine under aerobic conditions. This inhibition of proliferation was not observed under anaerobic conditions, indicating that L­histidine enhances oxidative DNA damage to E. coli cells. Reverse transcription­quantitative polymerase chain reaction analysis demonstrated that the expression of recA in E. coli MG1655 increased ~7­fold following treatment with 10 mM hydrogen peroxide (H2O2) plus 1% L­histidine, compared with that following exposure to H2O2 alone. L­histidine increased the genomic fragmentation of E. coli MG1655 following exposure to H2O2. In addition, L­histidine increased the generation of intracellular hydroxyl radicals in the presence of H2O2 in E. coli cells. Next, our group investigated the disinfection properties of the H2O2 and L­histidine combination. The combination of 100 mM H2O2 and 1.0% L­histidine significantly reduced the number of viable cells of extended­spectrum­ß­lactamase­producing E. coli and multidrug­resistant Pseudomonas aeruginosa, and this treatment was more effective than 100 mM H2O2 alone, but this effect was not observed in methicillin­resistant Staphylococcus aureus or vancomycin­resistant Enterococcus faecium. The combination of L­histidine and H2O2 may be a useful strategy to selectively increase the microbicidal activity of oxidative agents against Gram­negative bacteria.