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.

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 × 10⁵/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.

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).

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.