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The bactericidal action of peroxides; an E.P.R. spin-trapping study
P A Clapp1, M J Davies, M S French
1Department of Chemistry, University of York, Heslington, UK.
Free Radical Research
|September 1, 1994
Summary
Electron paramagnetic resonance (EPR) spin trapping detected carbon-centered and hydroxyl radicals during bacterial killing by peroxides. These radicals, particularly hydroxyl radicals, are the lethal species, with production linked to internal bacterial processes and iron-containing proteins.
Area of Science:
- Microbiology
- Biochemistry
- Chemical Biology
Background:
- Peroxide compounds exhibit bactericidal properties against Gram-negative and Gram-positive bacteria.
- The precise mechanism of bacterial death induced by peroxides, particularly the role of radical species, remains incompletely understood.
Purpose of the Study:
- To investigate radical production during the bactericidal action of peracetic acid, 4-percarboxy-N-isobutyltrimellitimide, and magnesium monoperoxyphthalate against Escherichia coli and Staphylococcus aureus.
- To identify the specific radical species responsible for bacterial cell death and elucidate their site of production within the bacterial cell.
Main Methods:
- Electron paramagnetic resonance (EPR) spin trapping using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to detect radical intermediates.
- Assessment of bactericidal activity and inhibition studies using antioxidants (Vitamin C, Trolox C) and iron chelators/haem protein inhibitors.
- Correlation of radical generation rates with bacterial kill percentages and peroxide concentration.
Main Results:
- Direct detection of carbon-centered and hydroxyl radicals produced during bacterial inactivation by peroxides.
- Antioxidants and DMPO inhibited bactericidal action, indicating radicals are lethal species, likely produced intracellularly.
- Hydroxyl radicals were identified as the primary lethal species, with their production influenced by bacterial type, peracid type and concentration, and involvement of iron species/haem proteins.
- A strong inverse correlation existed between observed radical adduct signal concentration and peroxide bactericidal strength, with potent bactericides generating radicals faster.
Conclusions:
- Radical production, particularly of hydroxyl radicals, is a key mechanism underlying the bactericidal action of peroxide compounds.
- Iron species and haem proteins play a significant role in the radical-generating process during bacterial inactivation.
- The rate of radical generation is directly proportional to the bactericidal efficacy of the peroxide compound.