EFFECT OF EXTRACELLULARLY GENERATED SINGLET OXYGEN ON GRAM-POSITIVE AND GRAM-NEGATIVE BACTERIA

In the separated surface-sensitizer system, a photosensitizer is physi cally separated from the substrate by a thin air layer under such cond itions that only singlet oxygen can reach and oxidize the substrate, p reventing the competition by type I photosensitized processes. This me thod has been used to study the reaction of singlet oxygen with Gram-p ositive (Streptococcus faecium) and Gram-negative (Escherichia coli) b acterial strains. Studies on cell samples exposed to singlet oxygen fo r different periods of time show a drastic decrease in survival for S. faecium, while E. coli becomes sensitive only when the integrity of t he outer membrane is altered by treatment with CaCl2 or roxymethyl)ami nomethane-ethylenediaminetetraacetic acid (Tris-EDTA). Biochemical and ultrastructural analyses suggest that the cytoplasmic membrane and th e genetic material are the main sites damaged by singlet oxygen.