Photodisinfection for the treatment of Biofilm Infections

Bacteria, which are single-celled organisms, generally exist in either a free-floating, unattached (planktonic) state or in an attached state called a biofilm.  A planktonic form suggests these single celled organisms float or swim independently of each other in some liquid medium.  A biofilm, or attached state, is created with a change of behaviour triggered by many factors, including quorum sensing. A biofilm is a complex community of a number of different microorganisms coexisting together and marked by the excretion of a protective and adhesive matrix. The biofilm is held together and protected by the matrix, called extracellular polymeric substance or exopolysaccharide (EPS), holds the biofilm together, protects the cells within it and facilitates communication among bacteria through biochemical signals.  In a biofilm, cells are closely packed together and firmly attached to each other and usually to a solid surface. 

Stages of Biofilm Development - Source: Wikipedia Commons

Bacteria living in a biofilm usually have significantly different properties from free-floating bacteria of the same species. This is due to the dense and protected environment of the bacteria within the biofilm which allows for various ways of opportunistic cooperation, communication, and interaction among the bacteria.  There are significant benefits to bacteria living in this environment such as greatly improved resistance to detergents and antibiotics since the dense extracellular matrix protects the interior realm of the bacterial community.  This environment promotes up to a 1000-fold increase in antibiotic resistance, meaning that bacteria within a biofilm community can withstand and resist the killing effects of antibiotics 1000 times more than same species of bacteria living in stand alone, free-floating non-biofilm environments.  In addition to greater antibiotic resistance, biofilm bacteria excrete toxins that generate immune responses from the host body unlike free floating organisms. 

Biofilms have been found to be involved in a wide variety of microbial infections in the body.  It is estimated that biofilm infections represent up to 80% of all human infections including: urinary tract infections, catheter infections, middle-ear infections, sinusitis, gum diseases, oral candidiasis, endocarditis, coating contact lenses, wound infections, infections in cystic fibrosis and infections of permanent implanted devices (e.g. heart valves, hip & knee replacements, tooth implants, etc.)   With the rise of antibiotic resistance then, it is imperative that non-antibiotic approaches to biofilm infections be developed. 

Photodisinfection (also known as antimicrobial Photodynamic Therapy or aPDT) has been shown over the past several decades to be highly effective in eradicating various microorganisms, including completely antibiotic resistant bacteria, known as superbugs, as well as their virulence factors.  Photodisinfection therefore provides both antimicrobial and anti-inflammatory benefits, which is a distinct advantage over antibiotics. Moreover, Photodisinfection is an instant process, with immediate antimicrobial results versus antibiotics which require 14 days or more of treatment.  My own research, since the mid 1990’s, on photoeradication of antibiotic resistant polymicrobial biofilms has demonstrated the effectiveness of this treatment in destroying antibiotic resistant bacteria and fungi biofilms.  In addition, we have demonstrated that repeated antimicrobial photodynamic therapy (aPDT) does not result in the development of bacterial resistance to PDT treatment, unlike with the repeated use of antibiotics.  This is a significant advantage of aPDT over conventional antibiotic treatments.  These studies have been confirmed by other reports in the literature of the efficacy of aPDT photodisinfection against biofilms and supports my contention that aPDT photodisinfection based products  should be developed to address the numerous applications for which current antibiotic treatments are ineffectual.  


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