Research Article: Effect of Sodium Chloride on Aggregation of Merocyanine 540 and Photosensitized Inactivation of Staphylococcus aureus and Pseudomonas aeruginosa

Date Published: , 2011

Publisher: A.I. Gordeyev

Author(s): T.A. Shmigol, V.A. Bekhalo, Е.V. Sysolyatina, E.V. Nagurskaya, S.A. Ermolaeva, A.Ya. Potapenko.



Merocyanine 540 (MC540) is used as a photosensitizer for the inactivation of
microorganisms. The following is already known about MC540: firstly, MC540
exists in distilled water in both monomeric and dimeric forms, and the addition
of salts into a MC540 solution leads to the formation of large aggregates that
can be detected by the resonance light scattering technique. Secondly, singlet
oxygen can only be photogenerated by MC540 monomers. In the present work, we
studied the effect of MC540 in the aggregated state on the rate of
photosensitized inactivation ofStaphylococcus
aureusandPseudomonas aeruginosa. To this end,
bacteria either in MC540-containing distilled water or in a 0.25 M sodium
chloride aqueous solution also containing MC540 are irradiated (546 nm). The
results show that, in the presence of salt, the aggregation of MC540 greatly
increases the efficiency of the MC540-photosensitized inactivation ofP.
aeruginosaandS. aureus. In the presence of salt,
the rates ofP. aeruginosaandS.
aureusinactivation increase by factors of 10 and 30, respectively, in
comparison with the rate of inactivation observed in the case of distilled
water. Our results suggest that a salt-induced photosensitization mechanism can
switch from the singlet oxygen to the free-radical pathway.

Partial Text

The search for effective methods of antibacterial protection has led to the
development of antimicrobial photodynamic therapy. The photodynamic effect was first
described by Raab in 1900, and the term “photodynamic reaction” was
first introduced by Tappeiner in 1904 [1]. The
photodynamic inactivation of bacteria occurs under the action of light in the
presence of photo-sensitizers (FSs) and molecular oxygen. Through exposure to light,
photosensitizers are activated, thereby producing free radicals or singlet oxygen,
which are fatal to infectious agents.


Absorption Spectra of MC540

It is known that the aggregation state of MC540 defines the type of photodynamic
reactions that occur and affects the formation of active products, which can inflict
damage on biological molecules [13] and can
also influence the rate of MC540 photobleaching [7, 8]. The production of singlet
oxygen ( 1 O 2 ) was believed to play the main role in the
bactericidal activity of photosensitizers [5,
14]. At the same time, it was shown that
singlet oxygen can generate only monomeric forms of MC540 [15].

The data obtained in this work indicating an increase in the bactericidal effects of
a photosensitizer in the presence of salts can be used in the development of
promising new antibacterial treatments especially in light of the current problems
connected with multiple antibiotic resistance.