UV Resistance of Bacillus anthracis Spores Revisited: Validation of Bacillus subtilis Spores as UV Surrogates for Spores of B. anthracis Sterne

Abstract

Recent bioterrorism concerns have prompted renewed efforts towards understanding the biology of bacterial spore resistance to radiation with a special emphasis on the spores of Bacillus anthracis. A review of the literature revealed that B. anthracis Sterne spores may be three to four times more resistant to 254-nmwavelength UV than are spores of commonly used indicator strains of Bacillus subtilis. To test this notion, B. anthracis Sterne spores were purified and their UV inactivation kinetics were determined in parallel with those of the spores of two indicator strains of B. subtilis, strains WN624 and ATCC 6633. When prepared and assayed under identical conditions, the spores of all three strains exhibited essentially identical UV inactivation kinetics. The data indicate that standard UV treatments that are effective against B. subtilis spores are likely also sufficient to inactivate B. anthracis spores and that the spores of standard B. subtilis strains could reliably be used as a biodosimetry model for the UV inactivation of B. anthracis spores.The October 2001 bioterrorist attack with Bacillus anthracis spores has sparked renewed interest in studying methods of bacterial spore inactivation and the mechanisms by which spores resist the lethal effects of various disinfection treatments. UV radiation at a 254-nm wavelength has been used as an efficient and cost-effective means of disinfecting surfaces (1,4,15,16,17), building air (3, 8, 13), and drinking water supplies (5). The most reliable method for testing the efficacy of UV disinfection equipment is biodosimetry, the use of a test organism to measure the biologically effective UV dose (2). Commonly used test organisms for UV biodosimetry studies are bacterial spores, usually spores of Bacillus subtilis, due to their high degree of UV resistance, reproducible inactivation response, and ease of use (reviewed in references 9 and 11). In particular, exhaustive testing of spores of the B. subtilis strain ATCC 6633 has resulted in this strain serving as the current European biodosimetry standard for 254-nm UV disinfection of drinking water (5).Semilogarithmic plots of spore inactivation versus UV fluence (dose) produce a characteristic curve, consisting of a shoulder at low UV doses, followed by a curve reflecting exponential inactivation at higher UV doses (Fig. 1). Two parameters often used to describe spore resistance to UV are (i) the UV dose lethal for 90% of the population (LD 90 ) and (ii) the decimal reduction value (D value), defined as the UV dose which reduces spore viability by a factor of 10, measured from the exponential portion of the inactivation curve (6, 11). For example, from the published data of Hoyer (5) (Fig. 1), it can be calculated that spores of B. subtilis ATCC 6633 exhibit an LD 90 and a D value of 260 and 120 J/m 2 , respectively (Table 1). In stark contrast to the extensively characterized UV inactivation response of B. subtilis spores, much less work has been performed to characterize the UV inactivation kinetics of B. anthracis ...

Survival of Spacecraft-Associated Microorganisms under Simulated Martian UV Irradiation

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Applications of a Rapid Endospore Viability Assay for Monitoring UV Inactivation and Characterizing Arctic Ice Cores

“…For that reason, they are employed as biological indicators for monitoring the effectiveness of sterilization processes, such as vaporized hydrogen peroxide treatments (17,19), autoclaving, and UV irradiation (25,30).…”

Modeling of ultraviolet (UV) radiation under a large pilot-scale designed for wastewater disinfection and inactivation of selected bacteria of Pseudomonas aeruginosa in a laboratory UV device

“…Therefore, the model of Chick-Watson, reduced to a first-order kinetic with n = 1, showing its limits, and that the inactivation process is most often non-uniform, and does not necessarily comply, as implies a first-order kinetics, with an exponential law (Shayeb et al, 1998;Nicholson and Galeano, 2003). In addition, the adopted experimental protocol showed a very noticeable reduction rate for low doses of irradiation.…”