Photodynamic UVA-riboflavin bacterial elimination in antibiotic-resistant bacteria.

BACKGROUND: To evaluate the bactericidal effect of clinical ultraviolet A (UVA) settings used in photoactivated chromophore for infectious keratitis (PACK)-collagen cross-linking (CXL) in antibiotic-resistant and non-resistant bacterial strains.

METHODS: Well-characterized bacterial strains from clinical isolates, without and with antibiotic resistance, were studied in a pairwise comparison. The evaluated pathogens were Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis. Bacteria were dispersed in PBS and diluted to a concentration of approximately 4 × 10(5) /ml. Riboflavin was added to a concentration of 0.01%. By spreading the solution on a microscope slide, a fluid film layer, with a thickness of around 400 mm, was formed and UVA exposure followed. Eight separate exposures were made for each strain (n = 8). The degree of elimination in resistant and non-resistant pathogens was compared.

RESULTS: The bactericidal efficacy of exposure differed between the tested microorganisms, and the mean elimination ranged between 60 and 92%, being most extensive in both of the evaluated Pseudomonas strains and least in the E. faecalis strains. Similar reductions were seen in antibiotic-resistant and non-resistant strains, with the exception of S. aureus, in which the resistant strain metchicillin-resistant Staphylococcus aureus (MRSA) was eradicated in a greater extent than the non-resistant strain (P = 0.030).

CONCLUSION: UVA-riboflavin settings used in PACK-CXL are effective in reducing both antibiotic-resistant and non-resistant bacteria. Antibiotic resistance does not appear to be protective against the photooxidative exposure.