Photodynamic treatment of the gram-negative bacteria Escherichia coli B and Acinetobacter baumannii and the gram-positive bacterium Staphylococcus aureus was performed using two newly devised and synthesized antioxidant carrier photosensitizers (antioxidant carrier sensitizers-2 [ACS-2] and antioxidant carrier sensitizers-3 [ACS-3]), which are butyl hydroxy toluene and propyl gallate substituted haematoporphyrins, respectively. It was found that ACS-2 is less reactive than other photosensitizers previously used for the same purpose, whereas ACS-3 is very effective against the multidrug-resistant bacterium A. baumannii, causing its complete eradication at a low fluence (approximately 7.5 J/cm2) of blue light (407-420 nm) and a low concentration (10 microM). At a higher fluence (approximately 37.5 J/cm2) complete eradication of E. coli B can be obtained under the same conditions. Furthermore, X-ray microanalysis and ultrastructural changes indicate that ACS-3, especially in the case of photodynamic treatment of A. baumannii, interferes with membrane functions and causes the inactivation of the bacterium. ACS-3 may be suggested as a specific photosensitization agent for photoinactivation of gram-negative bacteria.

Photodynamic treatment of the gram‐negative bacteria Escherichia coli B and Acinetobacter baumannii and the gram‐positive bacterium Staphylococcus aureus was performed using two newly devised and synthesized antioxidant carrier photosensitizers (antioxidant carrier sensitizers‐2 [ACS‐2] and antioxidant carrier sensitizers‐3 [ACS‐3]), which are butyl hydroxy toluene and propyl gallate substituted haematoporphyrins, respectively. It was found that ACS‐2 is less reactive than other photosensitizers previously used for the same purpose, whereas ACS‐3 is very effective against the multidrug‐resistant bacterium A. baumannii, causing its complete eradication at a low fluence (∼7.5 J/cm) of blue light (407–420 nm) and a low concentration (10 μM). At a higher fluence (∼37.5 J/cm) complete eradication of E. coli B can be obtained under the same conditions. Furthermore, X‐ray microanalysis and ultrastructural changes indicate that ACS‐3, especially in the case of photodynamic treatment of A. baumannii, interferes with membrane functions and causes the inactivation of the bacterium. ACS‐3 may be suggested as a specific photosensitization agent for photoinactivation of gram‐negative bacteria.

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