Photoantimicrobials as a potential local approach to geriatric UTIs

Aims: To test the efficacy of acceptable photoantimicrobial agents against bacterial pathogens implicated in complicated urinary tract infection (UTI) in comparison with conventionally employed antibacterials. Methods and Results: Toluidine blue (TB), methylene blue (MB), 5-aminolaevulinic acid (ALA), trimethoprim and levofloxacin were employed in the study against the typical UTI-implicated pathogens Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis and Proteus mirabilis. Standard bacterial cell culture was used to assay the activity both in the dark and under 660-nm LED-illuminated conditions. TB and MB were highly photoactive across the range and exhibited rapid kill rates, their effects being assayed after 20-min illumination, rather than the 18-h incubation employed with the other compounds. Trimethoprim was inactive against all bacteria except Pr. mirabilis, while levofloxacin maintained highly bactericidal activity throughout. ALA required high concentrations for effective action but, for porphyrin production in situ, also required an 18-h incubation. Conclusions: TB and MB were highly and rapidly photobactericidal in comparison with the remaining agents tested. Significance and Impact of the Study: Ubiquitous catheterization of geriatric patients offers a portal for light delivery to the urinary tract. The photoantimicrobial approach thus offers considerable potential.