Hydrogen Peroxide Augments the Disinfection Efficacy of 280 nm Ultraviolet LEDs against Antibiotic-Resistant Uropathogenic Otherwise Tolerant to Germicidal Irradiation.

The 280 nm ultraviolet light-emitting diode (UV LED) has emerged as a promising water disinfection technology and has been applied from point-of-use devices to municipal-scale systems. Accumulating evidence suggests that small numbers of antimicrobial-resistant bacteria can survive UV treatment; however, little research has been done to evaluate 280 nm UV alone or as part of advanced oxidation processes against these organisms. Here, we investigated 280 nm UV LED inactivation of a high-risk uropathogenic () strain belonging to clade A of the globally distributed, antimicrobial-resistant ST131 lineage known to persist in treated wastewater (ST131-A). We measured disinfection efficacy with and without hydrogen peroxide (HO) and assessed the reactivation of the treated bacteria in the light and dark. Our bench-scale modeling revealed that ST131-A displays UV tolerance, requiring 2.8 times more UV dose (35 mJ/cm) for 6-log inactivation compared to the reference strain ATCC 25922 (12.5 mJ/cm). Furthermore, we observed ∼1% photoreactivation of ST131-A even after UV doses of 90 mJ/cm, which is significantly greater than the operational minimums reported for the world's first 280 nm UV wastewater treatment plant. Analysis of a genome-edited bacterial model () suggests that bacterial reactivation following 280 nm UV treatment is linked to photolyase activity. The addition of 10-200 mg/L HO increased the inactivation of ST131-A 6,000-300,000-fold compared to UV or HO treatments alone, respectively. Chemical and microbiological analyses revealed that the mechanism of increased inactivation by combined treatments relied on UV photolysis of HO to generate hydroxyl radicals and residual HO activity that inhibited bacterial reactivation after treatment. Our findings suggest that some ST131 strains possess high UV tolerance, and that UV/HO treatment may effectively inactivate these multidrug- and UV-tolerant uropathogenic strains and thwart their reactivation in treated water.