Emerging investigator series: Inactivation of antibiotic resistant bacteria and inhibition of horizontal resistance gene transfer is more effective by 222 than 254 nm UV†

Abstract

The presence of antibiotic resistant bacteria (ARB) and the horizontal gene transfer (HGT) of antibiotic resistant genes (ARGs) in water environments pose a large and increasing threat to human health. This work compares the treatment efficiency of different ultraviolet (UV) wavelengths (222 nm KrCl excimer lamp and 254 nm low pressure Hg lamp) for inactivating multidrug antibiotic resistant B. subtilis strain 1A189, damaging its intracellular and extracellular ARGs, and inhibiting HGT of ARGs into non-resistant strain 1A1. The 222 nm wavelength was more effective than 254 nm at inactivation (dose required for 1 log reduction or D₁ = 4.11 mJ cm⁻² at 222 nm and 8.99 mJ cm⁻² at 254 nm). ARG damage increased with dose and with increasing qPCR amplicon length for both UV wavelengths. Although extracellular ARG damage was similar between wavelengths, intracellular ARG damage was greater at 222 nm than 254 nm. Inhibition of HGT also increased with UV dose for both wavelengths, but was stronger at 222 nm for both extracted DNA (D₁ 8.57 mJ cm⁻² at 222 nm and 50.23 mJ cm⁻² at 254 nm) and intracellular DNA (D₁ = 20.14 mJ cm⁻² at 222 nm and 92.90 mJ cm⁻² at 254 nm). When taking into account factors such as electrical efficiency and spectral absorbance that are less favorable for 222 nm, results showed that 222 nm was still more efficient at extracellular HGT inhibition, while 254 nm was more efficient for other assay endpoints. Overall, these comparisons demonstrate the superior mechanistic efficacy of 222 nm over 254 nm UV for disinfecting ARB and for inhibiting transfer of ARG despite similar ARG damage. This information will help inform and improve tools to address the global water challenge of antibiotic resistance to minimize risks to human health.