Stomping Out Staph Infections with PDT

Hospital infections are all too common these days, and many of these situations involve the bacteria that medical professionals refer to as staph, the shorthand for Staphylococcus aureus. The microbe is blamed for a wide range of infectious problems such as abscesses, boils, wound infections, cellulitis, and toxic shock syndrome.  Within the hospital setting, staph infections are typically spread by medical devices (e.g., catheters) or by a medical professional touching a patient’s skin. The bacteria infect openings in the skin such as scratches, pimples, or skin cysts. Once the microbes enter the body, they can spread to the blood, bones, joints, and even organs such as the brain, heart, and lungs.

A key concern regarding staph infections is their tendency to be resistant to antibiotic treatment.  The best studied of these strains is methicillin-resistant Staphylococcus aureus, or MRSA.  These bacteria do not respond to treatment with certain antibiotics, including various penicillins. MRSA can be carried in airborne droplets and then transmitted when an individual inhales particles of infected sputum from the air. The bacteria can become airborne when an infected person speaks, coughs, or sneezes, thus expelling saliva.

Each year, according to WHO figures, there are about 440,000 new cases of multidrug-resistant tuberculosis, resulting in at least 150,000 deaths.  A high percentage of hospital-acquired infections can be traced to highly resistant bacteria, notably MRSA. In Europe, MRSA rates have been increasing in Germany, Belgium, Ireland, the Netherlands, and the United Kingdom. Far more MRSA cases have been reported in southern and western Europe than in northern Europe.  Recently, MRSA infections have been identified in otherwise healthy people who had not undergone hospitalization or invasive medical procedures within the preceding year.

What these troubling facts and figures tell us is that antibiotic resistance may very soon reach a critical threshold. This could mean that we may no longer be able to use the same approach to the problem of infectious disease. The good news is that the use of photodynamic therapy, or PDT, can circumvent the problem of antibiotic resistance, yet still overcome infectious disorders.

According to Dr. Michael Hamblin and his colleagues at the Wellman Center for Photomedicine in Boston, Massachusetts (USA), PDT has had beneficial effects against MRSA and other antibiotic resistant microbes because it is not constrained by the same factors that limit antibiotic treatment.  Hamblin’s point is supported by a flood of recent studies that show that so-called antimicrobial PDT can effectively eliminate MRSA infections and may even be used for combating MRSA contamination of foods.

Researchers at the University of Milan (Italy) found that PDT disrupts the biofilm formation of MRSA on prosthetic material.  This has major relevance given the growing public health concern posed by prosthetic joint infections.  As more people undergo joint replacement surgery (hip or knee replacements in particular) in developed countries, such MRSA infections are becoming more and more common.  Biofilm is a strategy that MRSA uses to stay resistant to antibiotics, as well as to shield the bacteria from the immune system.  Thus, PDT may be useful approach to the treatment of prosthetic joint infections, as reported in the July 2014 International Journal of Antimicrobial Agents.

Protecting the Food Supply

Another potential application of photodynamic principles concerns the food chain, which serves as a major vehicle for the transfer of MRSA and other resistant bacteria from animals to humans. A recent study out of the University of Salzburg (Austria) focused on using “photodynamic inactivation” using the natural plant compound curcumin, which comes from the East Indian spice turmeric.  More specifically, the researchers used curcumin bound to polyvinylpyrrolidone (PVP-C) and NovaSol®-curcumin as photosensitizers.

They hypothesized that these curcumin-based photosensitizers could serve as a potent tool for the decontamination of cucumber, pepper and chicken meat from Staphylococcus aureus (S. aureus, serving as the model for MRSA). Both curcumin and PVP have been approved as food additives.  In this study, vegetables and meat were contaminated with S. aureus and sprinkled with the curcumin photosensitizers, followed by illumination with visible light.

Additionally, the long-term effects of the photodynamic inactivation on cucumbers were investigated by quantitative analyses of the viable bacterial fraction after 24 and 48 hours. Photodynamic inactivation of S. aureus revealed an average reduction of 99.8% for cucumbers, 99.7% for pepper and 98% for chicken meat relative to the control samples. The bacteria-killing effect compared to controls seems to last for at least 48 hours, and no visible changes of the exterior appearance of foodstuff after photodynamic decontamination were observed.

Thus, as the Austrian authors state in the 24 June 2014 issue of Photochemical & Photobiological Sciences, “photodynamic inactivation may therefore constitute a safe, economic and effective decontamination technique, which is harmless to health and not noticeable to consumers”.

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Sources

Rosa LP1, da Silva FC, Nader SA, Meira GA, Viana MS. In vitro effectiveness of antimicrobial photodynamic therapy (APDT) using a 660 nm laser and malachite green dye in Staphylococcus aureus biofilms arranged on compact and cancellous bone specimens. Lasers Med Sci. 2014 Jun 17. [Epub ahead of print]

Vassena C1, Fenu S2, Giuliani F3, Fantetti L3, Roncucci G3, Simonutti G2, Romanò CL4, De Francesco R2, Drago L5. Photodynamic antibacterial and antibiofilm activity of RLP068/Cl against Staphylococcus aureus and Pseudomonas aeruginosa forming biofilms on prosthetic material. Int J Antimicrob Agents. 2014 Jul;44(1):47-55.

Rineh A, Kelso MJ, Vatansever F, Tegos GP, Hamblin MR. Clostridium difficile infection: molecular pathogenesis and novel therapeutics. Expert Rev Anti Infect Ther. 2014 Jan;12(1):131-50.

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