Overview of the Inactivation by 254 nm Ultraviolet Radiation of Bacteria with Particular Relevance to Biodefense

Abstract

Our goal was to ultimately predict the sensitivity of untested bacteria (including those of biodefense interest) to ultraviolet (UV) radiation. In this study, we present an overview and analysis of the relevant 254 nm data previously reported and available in the literature. The amount of variability in this data prevented us from determining an ''average'' response for any bacterium. Therefore, we developed particular selection criteria to include the data in our analysis and suggested future guidelines for reporting UV sensitivity results. We then compiled a table of the sensitivity to 254 nm UV for 38 bacteria and three bacterial spores. The UV sensitivity was quite similar (within 10%) among the spores of Bacillus anthracis (strains Vollum 1B and Sterne), Bacillus subtilis, and Bacillus megaterium. These data indicate that spores of B. subtilis and B. megaterium could be adequate simulants of B. anthracis spores in UVC experiments. Spores of B. anthracis, B. subtilis and B. megaterium were 5-10 times more resistant to UV than were their corresponding vegetative cells. The vegetative cells of B. anthracis showed similar UV sensitivity to those of Burkholderia pseudomallei, Shigella sonnei, and a wild-type strain of Escherichia coli. Yersinia enterocolitica and Vibrio cholerae appeared more sensitive to UV and Salmonella typhi slightly more resistant to UV than E. coli. The sensitivity (at 254 nm) of all vegetative bacteria ranged from 11 to 80 Jm 2 for a 1 Log 10 kill and from 25-200 Jm 2 for 4 Log 10 kill.

Germicidal UV Sensitivity of Bacteria in Aerosols and on Contaminated Surfaces

“…, reviewed in Table 1 of Coohill and Sagripanti 2008 Peccia et al 2001). This difference in the aerodynamic diameter of vegetative cells could account for different UV sensitivities measured in this and in previous studies.…”

“…Our measurements demonstrated that after 1 min mixing inside the chamber, samples of air at three different locations contained viable bacteria that differed in concentration less than 1.6% between sites. In addition, the curves of semi-logarithmic UV inactivation versus time appearing approximately linear without apparent "toes," (Coohill and Sagripanti 2008) indicate that our samples consisted in relatively homogeneous cell populations. Since the effect of UV intensity on cell inactivation is generally linear through a relatively broad range, cell survival can be extrapolated to other UV dose.…”

“…This shoulder region (which was also observed for P. agglomerans up to 60 s in Figure 5) reflects the ability of cells to endure small amounts of damage and/or to repair the damage produced by the relatively low exposures (Coohill and Sagripanti 2008) The values shown in Figure 5 correspond to cells exposed to an average flux of 0.54 ± 0.06 W.m −2 calculated by contour analysis of flux inside the chamber (see Results). Collection of aerosolized bacteria at various locations indicated that the mixing condition employed inside the chamber produced a relatively homogeneous distribution of aerosols throughout the exposure chamber in less than 1 min (see Characterization of Aerosol Exposure above).…”

“…Even fewer data is available for human pathogens and still even fewer for microbes of interest in biodefense. Previous efforts in ours and other laboratories have focused on spores of B. anthracis and other Bacillus species Sagripanti et al 2007), particularly on B. subtilis spores whose sensitivity has been studied in all UV regions, including UVC (Coohill and Sagripanti 2008). In contrast, less data is available on the sensitivity of Bacillus cells in the vegetative state, before sporulation or after germination.…”

“…Since some data for Bacillus spores is already available we were particularly interested in the airborne inactivation kinetics of B. atrophaeus cells in vegetative state. The inactivation by UVC of vegetative cells of B. anthracis (Knudson 1986) and B. subtilis (Peccia et al 2001) has been studied previously but comparison of the inactivation kinetics of vegetative cells of Bacillus species is limited (Coohill and Sagripanti 2008). In addition, it is difficult to correlate the more extensive body of data obtained on contaminated surfaces or on liquid suspensions to the sensitivity to UVC of microorganisms in aerosols since data is generally obtained for organisms either on surfaces or in aerosols but seldom in both states.…”