Inactivation kinetics and lethal dose analysis of antimicrobial blue light and photodynamic therapy

Abstract

Background: Photodynamic therapy (PDT) has been long used to treat localized tumors and infections. Currently, microbial inactivation data is reported presenting survival fraction averages and standard errors as discrete points instead of a continuous curve of inactivation kinetics. Standardization of this approach would allow clinical protocols to be introduced globally, instead of the piecemeal situation which currently applies. Methods: To this end, we used a power-law function to fit inactivation kinetics and directly report values of lethal doses (LD) and a tolerance factor (T) that informs if inactivation rate varies along the irradiation procedure. A deduced formula was also tested to predict LD for any given survival fraction value. We analyzed the photoantimicrobial effect caused by red light activation of methylene blue (MB-APDT) and by blue light (BL) activation of endogenous microbial pigments against 5 clinically relevant pathogens. Results: Following MB-APDT, E. coli and S. aureus cells become increasingly more tolerant to inactivation along the irradiation process (T<1). K. pneumoniae presents opposite behavior, i.e., more inactivation is observed towards the end of the process (T>1). P. aeruginosa and C. albicans present constant inactivation rate (T~1). In contrast, all bacterial species presented similar behavior during inactivation caused by BL, i.e., continuously becoming more sensitive to blue light exposure (T>1). Conclusion: The power-law function successfully fit all experimental data. The analytical model precisely predicted LD and T values. We expect that these analytical models may contribute to more standardized methods for comparisons of photodynamic inactivation efficiencies.

Global priority multidrug-resistant pathogens do not resist photodynamic therapy

“…All inactivation kinetics data were fitted by power-law (eq. 1) for statistical comparison of each inactivation kinetics curve according to Sabino et al [20]. LD90 and T (tolerance factor) values were initially obtained for each strain by non-linear regression analysis.…”

“…We performed standard aPDT susceptibility tests based on the study published by Sabino et al [20]. Inocula were prepared from overnight broth cultures under shaking regimen.…”

Factors Determining the Susceptibility of Bacteria to Antibacterial Photodynamic Inactivation

“…Other literature data showed that P. aeruginosa pyoverdine blue pigment can absorb visible light at 415 nm. This property suggests that this pyoverdine can participate in photodynamic reactions because it can absorb visible light ( 100 ). Colorful pigments are also found in Prevotella intermedia and Prevotella nigriscens , which are microorganisms able to colonize the oral cavity that are capable of producing black pigments.…”

UV-C (254 nm) lethal doses for SARS-CoV-2

“…Results were normalized in relation to controls for the calculation of viral inhibition rates of each sample. For the viral inactivation kinetics, we used the methodology reported by Sabino et al [ 5 ].…”