Since the early 1990s, it has been proven that bacteria causing diseases in humans are able to form biofilms. Their capability of producing biofilms are associated with chronic infectious diseases. One of them is Staphylococcus aureus (S.aureus).

S. aureus is a normal flora that lives commensally on the skin, nasal passages, or human throat. Under abnormal conditions, these bacteria can cause several diseases, from minor skin diseases such as skin infections, acne vulgaris, cellulitis folliculitis to serious illnesses such as pneumonia, meningitis, osteomyelitis endocarditis, toxic shock syndrome, and septicemia.

Staphylococcus aureus infection can also be caused by direct contamination of the wound, for example, in postoperative wound infections or infections after trauma.

Biofilms are a community of structured and attached bacteria cells. These bacteria can produce polymeric matrices and attach to biological surfaces and inanimate matter.

This formation makes the biofilm-making bacteria able to withstand extreme environments. The bacteria in the biofilm are able to withstand antibiotics, disinfectants, and even be able to withstand the host’s immunity system.

The clinical manifestation of infection by biofilm-forming bacteria is resistant to antibiotic treatment. Antibiotic therapy, in general, will only kill the cells of the planktonic bacteria (which swim outside the biofilm), while the form of bacteria that are tightly arranged in the biofilm will stay alive and develop and will release the form of planktonic cells out of biofilm formation. So an alternative method effective and selective is needed to eradicate S.aureus biofilm bacteria. One of them is a photodynamic method using light and photosensitizers.

Naturally, some bacteria contain porphyrin compounds as endogenous photosensitizer molecules which are sensitive to light. The results showed that light irradiation with a wavelength spectrum appropriate with the spectrum of porphyrin photosensitizer absorption in the correct dose of irradiation energy could cause photoinactivation of bacterial cells. Photoinactivation is the inhibition of cell metabolic activity because of damage to the cytoplasmic membrane due to peroxidation by reactive oxygen on lipids and proteins resulting in cell lysis or inactivation of the membrane transport system and membrane transport enzyme system in these bacterial cells.

The mechanism of photoinactivation involves the process of photosensitization. It is the process of light absorption by bacterial porphyrins, which subsequently activate the occurrence of further chemical reactions resulting in various reactive oxygen species. Photosensitization depends on the type and quantity of photosensitizer and the suitability of the light spectrum with the spectrum of photosensitizer absorption.

Photosensitizer quantity can be increased by administering exogenous photosensitizer. The exogenous photosensitizer is photosensitizer added to increase the absorption of light photons. There are various kinds of photosensitizer, either organic or metal. The organic photosensitizer is generally extracted from natural materials such as chlorophyll from green plants and photosynthetic bacteria while metal photosensitizer is generally synthesized from metals such as gold, silver, and so on.

One light source that is suitable with photosensitizer porphyrin absorption spectrum is laser (Light Amplification by Stimulated Emission of Radiation). The laser is electromagnetic waves that propagate without going through a medium. Physical characteristics distinguishing laser light from other light are: coherent (space and time), monochromatic, the beam is very sharp and has a high intensity. One type of laser used in photodynamic applications is diode laser such as Gallium-aluminum-Arsenide (Ga-Al-As) and Gallium-Arsenide (Ga-As). The laser diode has advantages in terms of physical size. It is small, lightweight, portable, not easily broken and simple in assembly with a relatively low price so it is suitable for photodynamic applications.

The effects of visible light on organisms have been investigated at different levels of complexity. The photochemical product in the form of a singlet physical oxygen (ROS) is an oxidizing agent that can directly react with many biological molecules.

The amino acid residues in proteins are important targets such as cysteine, methionine, tyrosine, histidine, and tryptophan. Singlet oxygen ( ¹O ₂) is electrophilic and it reacts with electron-rich molecules causing membrane damage due to lipid peroxidation, resulting in leakage of contents and contents in cells and inactivating membrane transport systems and enzymes, disruption of cell wall synthesis and the emergence of multilamellar structures next to dividing cells, along with the leak of potassium ions from inside the cell. Various research results have shown the photodynamic success of inactivation using a diode laser to reduce biofilms without causing resistance to bacteria. So the photodynamic method as one method of bacterial inactivation is very promising in the future.

Author: Suryani Dyah Astuti

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