ANTIBACTERIAL ACTIVITY OF TRIARYLMETHANE DERIVATIVES ON STAPHYLOCOCCUS AUREUS.

PAEZ P. L.; AIASSA I; ALBESA I; BECERRA M C; ARGÜELLO GA

Otro; 1ª Reunión Internacional de Ciencias Farmacéuticas; 2010

Antibacterial activity of triarylmethane derivatives on Staphylococcus aureus.

Paez, PL (1,2), Aiassa Martínez IM ⁽¹⁾, Albesa I ⁽²⁾, Becerra MC ⁽²⁾ and Argüello GA ^(1)#.

⁽¹⁾INFIQC-CONICET, Dpto. de Fisicoquímica; ⁽²⁾Dpto. de Farmacia, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba. Ciudad Universitaria. 5000 Córdoba. República Argentina.

Introduction

PHOTODYNAMIC THERAPY (PDT) is based on the concept that certain photosensitizers (PS) can be localized in neoplasic tissue and subsequently be activated with the appropriate wavelength of light to generate active molecular species that produce toxicity in cells and tissues (1,2).

                Antimicrobial PDT research has increased in the last 20 years because of concerns resulting from the emergence of antibiotic-resistant bacterial strains. The control of infections by chemotherapic agents is often jeopardized by the spreading of bacterial strains resistant to many conventional antibiotics. As PDT is a multi-target process, it is unlikely to induce resistance in microorganisms (3).   

Materials and methods

Staphylococcus aureus ATCC 29213 was grown aerobically in trypticase soy broth.  

The antimicrobial activity of the compounds was evaluated by using the standard tube dilution method on Mueller Hinton Broth. Bacterial growth was observed at 18 h of incubation, following the indications of the Clinical and Laboratory Standards Institute.

A macrodilution method was used to determine the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC).

Bacterial suspensions incubated with New Fuchsin (NF⁺) were irradiated at 0, 1, 6, 18 and 24 h and incubated for 18 h to 37 ºC. Reactive oxygen species (ROS) were investigated by reduction of Nitro blue Tetrazolium.

Results

S. aureus was found to be susceptible to NF⁺ with a MIC and MBC of 1 µg/mL. Malachite green (MG⁺) showed the highest activity with a MIC of 0.002µg/mL and a MBC of 0.063µg/mL while Crystal Violet (CV⁺) showed a MIC of 0.098µg/mL and a MBC of 0.39µg/mL.

When S. aureus cultures (10⁶ CFU/mL), without NF, were illuminated for 24 h, they did not decrease the number of viable cells. In the presence of NF and light treatment, the percentages of survivors after 1, 6, 18 and 24 h were reduced by 1.4 %, 1.5%, 93.2% and 93.9%, respectively. Thus, increasing the time of the contact between the PS and the bacterial cells has improved the performance of the PS against the mentioned bacteria.

An efficient photoinactivation of S. aureus was obtained from a light exposure time of 6 h. shorter irradiation times did not further affect the percentage of photoinactivated bacteria.

The results obtained for ROS generation at all concentrations and times assayed showed similar values to the controls.

Conclusions

The photodynamic therapy with NF may be an effective bactericidal method against S. aureus and potentially against other bacterial pathogens. The ROS are not involved in the mechanism of bacterial killing. We conclude that the most important species involved in the mechanism of bacterial killing is the triarylmethane (TAM⁺) radical principally from the TAM⁺ triplet state.

Acknowledgments

UNC, CONICET, SeCyT, ANPCyT.

References.

[[1]]         Dougherty TJ. Photosensitizers: Therapy and detection of malignant tumors. Photochem. Photobiol 1987;45,879-89.

[2]         Henderson BW, Dougherty TJ. Photodynamic therapy: basic principles and clinical applications. Marcel Dekker Inc., New York; 1992.   

[3]         Ferraudi G, Argüello GA, Ali H, van Lier JE. Type I and II sensitized photooxidation of aminoacid by phthalocyanines: A flash photochemical study. Photochem. Photobiol 1988;47,657-60.