Antimicrobial blue light and photodynamic therapy inhibit clinically relevant 8-lactamases with extended-spectrum (ESBL) and carbapenemase activity

Introduction: The production of beta-lactamases by Gram-negative bacteria is among the most important factors of resistance to antibiotics, which has contributed to therapeutic failures that currently threaten human and veterinary medicine worldwide. Antimicrobial photodynamic therapy and antimicrobial blue light have a broadspectrum antibacterial activity against multidrug-resistant and hypervirulent pathogens. Objective: To investigate the ability of antimicrobial blue light to inhibit the hydrolytic activity of clinically relevant beta-lactamase enzymes (i.e., KPC, IMP, OXA, CTX-M, and SHV), with further comparison of the inhibitory effects of antimicrobial blue light with methylene blue-mediated antimicrobial photodynamic therapy. Methods: Blue LED light (A = 410 +/- 10 nm) alone or red LED light (A = 660 +/- 10 nm) in combination with methylene blue were used to inactivate, in vitro, suspensions of Klebsiella pneumoniae strains producing clinically important beta-lactamase enzymes assigned to the A, B and D Ambler molecular classes. Furthermore, beta-lactamase activity inhibition mediated by antimicrobial blue light and methylene blue-mediated antimicrobial photodynamic therapy was measured by using the chromogenic beta-lactam substrate nitrocefin. Results: beta-lactamase activities were effectively inactivated by both visible light-based approaches. In this regard, antimicrobial blue light and methylene blue-antimicrobial photodynamic therapy led to a significant reduction in the hydrolysis of nitrocefin (81-98 %). Conclusion: Sublethal doses of antimicrobial blue light and methylene blue-mediated antimicrobial photodynamic therapy are equally effective to inhibit clinically significant beta-lactamases, including extended-spectrum beta-lactamases and carbapenemases.