Author(s): Wanessa CMA de Melo 1 2 3 , Pinar Avci 1 2 , Milene Nóbrega de Oliveira 3 , Asheesh Gupta 1 2 4 , Daniela Vecchio 1 2 , Magesh Sadasivam 1 5 , Rakkiyappan Chandran 1 5 , Ying-Ying Huang 1 2 , Rui Yin 1 2 6 , Livia R Perussi 7 , George P Tegos 1 2 8 9 , Janice R Perussi 3 , Tianhong Dai 1 2 , Michael R Hamblin [*] 11 2 10
antimicrobial photodynamic therapy; biofilm; dental infection; extracellular polysaccharide; microbial resistance; multidrug efflux pump; persister cells; photosensitizers
It has been discovered in recent years that biofilms are responsible for a wide variety of microbial infections in the body; this could be as high as 80% of all infections  . Infectious diseases for which microbial biofilms have been held responsible include urinary tract infections, catheter infections, middle-ear infections, gingivitis, caries, periodontitis, orthopedic implants, some gastrointestinal infections, and so on  . Microbial biofilms can be defined as communities of surface-attached microbial cells firmly encased in a layer of extracellular matrix (ECM). These communities have a well-developed communication system that allows them to regulate microbial growth and metabolism. Furthermore, the biofilm lifestyle confers resistance to antimicrobials, and prevents access by host inflammatory cells and can also alter host metabolism [3,4] .
Infections by bacterial biofilms are typified by the ability of the bacteria in the biofilms to adapt themselves in undesirable environments with nutrient deficiency, presence of antibiotics and adverse environmental conditions as well as immunological defenses. These microorganisms tend to grow by adhering themselves onto biotic or abiotic surfaces and also onto medical devices implanted into various body parts. These have been a major cause of concern because of the difficulty faced by antimicrobial agents in penetrating the ECM of the biofilm. Owing to the serious nature of these infections and the near-complete death of effective strategies for treating them, novel ways to combat biofilms need to be discovered and developed.
Antimicrobial photodynamic therapy (aPDT), also known as photodynamic inactivation (PDI) or photodynamic antimicrobial chemotherapy, has been reported to be effective in eradicating both planktonic cells and biofilms. aPDT basically involves the synergistic combination of a photosensitizer (PS), molecular oxygen and visible light of appropriate wavelength in order to produce highly reactive oxygen species (ROS), which leads to the oxidation of several cellular components and to rapid cell inactivation. This review will focus on the use of aPDT in the inactivation of biofilms as schematically illustrated in Figure 1.
Biofilm is a lifestyle that microorganisms adopt to survive in certain harsh environments. Most biofilms are formed in nature by more than one species that may be attached to a biotic or an abiotic surface. A mixture of polysaccharides is secreted and assembled into biofilm by a monospecies or by multiple species, so that they can survive and grow  .
The known types of organisms that can grow in biofilms include various pathogenic bacteria and fungi. Despite these small organisms, the formation of communities in these systems is very complex and involves different factors. The mechanism...