Showing papers by "Maria A. F. Faustino published in 2016"

Effect of photodynamic therapy on the virulence factors of Staphylococcus aureus

Abstract: Staphylococcus aureus is a Gram-positive bacterium that is present in the human microbiota. Nevertheless, these bacteria can be pathogenic to the humans. Due to the increasing occurrence of antibiotic-resistant S. aureus strains, new approaches to control this pathogen are necessary. The antimicrobial photodynamic inactivation (PDI) process is based in the combined use of light, oxygen, and an intermediary agent (a photosensitizer). These three components interact to generate cytotoxic reactive oxygen species that irreversibly damage vital constituents of the microbial cells and ultimately lead to cell death. Although PDI is being shown to be a promising alternative to the antibiotic approach for the inactivation of pathogenic microorganisms, information on effects of photosensitization on particular virulence factors is strikingly scarce. The objective of this work was to evaluate the effect of PDI on virulence factors of S. aureus and to assess the potential development of resistance of this bacterium as well as the recovery of the expression of the virulence factors after successive PDI cycles. For this, the photosensitizer 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin tetra-iodide (Tetra-Py(+)-Me) and six strains of S. aureus [one reference strain, one strain with one enterotoxin, two strains with three enterotoxins and two methicillin resistant strains (MRSA) - one with five enterotoxins and the other without enterotoxins] were used. The effect of photosensitization on catalase activity, beta hemolysis, lipases, thermonuclease, enterotoxins, coagulase production, and resistance/susceptibility to methicillin was tested. To assess the development of resistance after successive cycles of treatment, three strains of S. aureus (ATCC 6538, 2065 MA, and SA 3 MRSA) were used. The surviving colonies of a first cycle of PDI were collected from the solid medium and subjected to further nine consecutive cycles of PDI. The results indicate that the expression of some external virulence factors is affected by PDI and enterotoxin producing strains were more susceptible to PDI than non-toxigenic strains. The surviving bacteria did not develop resistance. PDI, contrarily to traditional antibiotics, inhibited the expression of virulence factors, efficiently inactivating either highly virulent strains and low virulent S. aureus strains, inactivating also antibiotic susceptible and resistant strains, without development of photoresistance after at least 10 consecutive cycles of treatment, and so this therapy may become a strong promising alternative to antibiotics to control pathogenic microorganisms.

Indirect and direct damage to genomic DNA induced by 5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin upon photodynamic action

Abstract: Photodynamic inactivation has been proposed as an efficient antimicrobial treatment for localized infections. Even though it is generally accepted that the cell wall and membrane components are the main targets of the photodynamic process, the importance of the nucleic acids as photodynamic targets is not yet fully understood. In this study, we investigated the photodamage of the genomic nucleic acids of the Gram negative bacterium Escherichia coli, using 5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin tri-iodide (Tri-Py+-Me-PF) as photosensitizing agent. We tested, for the first time, the indirect photodamage effects on genomic DNA extracted from photosensitized bacteria and compared it with the direct effects on genomic DNA extracted from non-photosensitized cells, treated in otherwise similar experimental conditions. The results suggest that DNA does not seem to be a major target of photodynamic inactivation, once direct exposure to photosensitization does not damage DNA and does not significantly alter DNA concentration. The decrease in DNA concentration observed during the indirect exposure to photosensitization is directly related with the reduction of the concentration of bacterial cells. However, RNA synthesis was severely affected, once an indirect effect on proteins involved in the transcription process may cause a marked decrease in the RNA pool.