Study of the Bactericidal Efficacy of Short-Wave UV Irradiation on Pathogenic Klebsiella pneumoniae, Moraxella catarrhalis, and Kocuria rhizophila by Confocal Laser Scanning Microscopy.

The effect of UV radiation in the range of 185-254 nm on the viability of stress-resistant dormant forms of Moraxella catarrhalis, Kocuria rhizophila and biofilm-forming Klebsiella pneumoniae was studied. This bacterial form is much more resistant to UV irradiation in comparison with vegetative (planktonic) cultures. The antimicrobial efficacy of the experimental UV emitter (Ishlinsky Institute for Problems in Mechanics, Russian Academy of Sciences) was studied by confocal microscopy with differentiated staining of live/dead cells of K pneumoniae, M. catarrhalis, and K. rhizophila. For the first time, synergistic effects of UV irradiation in combination with biological and physical factors were demonstrated. When phage-encoded depolymerase Dep_kpv74 was added and followed by UV irradiation, the number of dead cells in K. pneumoniae biofilms increased from 81 to 91%. The combined effect of UV radiation and ozone on K. rhizophila dormant form resulted in cell death in 94% of cases. M. catarrhalis dormant forms were more resistant to UV irradiation (55% dead cells) in comparison with irradiated vegetative cells (72% dead cells). The results obtained have great practical and fundamental significance. They demonstrate the high survival rates of stress-resistant forms of pathogenic bacteria in the environment. They also show that new bactericidal devices operated at different wavelengths are required to prevent the spread of pathogens causing infectious diseases.