Hot, humid air decontamination of a C-130 aircraft contaminated with spores of two acrystalliferous Bacillus thuringiensis strains, surrogates for Bacillus anthracis

Review of techniques for the in-situ sterilization of soil contaminated with Bacillus anthracis spores or other pathogens

This review summarizes the literature on efficacy of techniques to sterilize soil. Soil may need to be sterilized if contaminated with pathogens such as Bacillus anthracis. Sterilizing soil in-situ minimizes spread of the bio-contaminant. Soil is difficult to sterilize, with efficacy generally diminishing with depth. Methyl bromide, formaldehyde, and glutaraldehyde are the only soil treatment options that have been demonstrated at full-scale to effectively inactivate Bacillus spores. Soil sterilization modalities with high efficacy at bench-scale include wet and dry heat, metam sodium, chlorine dioxide gas, and activated sodium persulfate. Simple oxidants such as chlorine bleach are ineffective in sterilizing soil.

Dose-response analysis of Bacillus thuringiensis HD-1 cry- spore reduction on surfaces using formaldehyde with pre-germination

AIM

To establish a basis for rapid remediation of large areas contaminated with Bacillus anthracis spores.

METHODS AND RESULTS

Representative surfaces of wood, steel and cement were coated by nebulization with B. thuringiensis HD-1 cry- (a simulant for B. anthracis) at 5.9 ± 0.2, 6.3 ± 0.2 and 5.8 ± 0.2 log10 CFU per cm² , respectively. These were sprayed with formaldehyde, either with or without pre-germination. Low volume (equivalent to ≤2500 L ha^-1 ) applications of formaldehyde at 30 g l^-1 to steel or cement surfaces resulted in ≥4 or ≤2 log10 CFU per cm² reductions respectively, after 2 h exposure. Pre-germinating spores (500 mmol l^-1 l-alanine and 25 mmol l^-1 inosine, pH 7) followed by formaldehyde application showed higher levels of spore inactivation than formaldehyde alone with gains of up to 3.4 log10 CFU per cm² for a given dose. No loss in B. thuringiensis cry- viability was measured after the 2 h germination period, however, a pre-heat shock log10 reduction was seen for B. anthracis strains: LSU149 (1.7 log10), Vollum and LSU465 (both 0.9 log10), LSU442 (0.2 log10), Sterne (0.8 log10) and Ames (0.6 log10).

CONCLUSIONS

A methodology was developed to produce representative spore contamination of surfaces along with a laboratory-based technique to measure the efficacy of decontamination. Dose-response analysis was used to optimize decontamination. Pre-germinating spores was found to increase effectiveness of decontamination but requires careful consideration of total volume used (germinant and decontaminant) by surface type.

SIGNIFICANCE AND IMPACT OF THE STUDY

To be practically achievable, decontamination of a wide area contaminated with B. anthracis spores must be effective, timely and minimize the amount of materials required. This study uses systematic dose-response methodology to demonstrate that such an approach is feasible.

Ultraviolet dosage and decontamination efficacy were widely variable across 14 UV devices after testing a dried enveloped ribonucleic acid virus surrogate for SARS-CoV-2

Aims: The dosages and efficacy of 14 ultraviolet (UV) decontamination technologies were measured against a SARS-CoV-2 surrogate virus that was dried onto different materials for laboratory and field testing.

Methods and results: A live enveloped, ribonucleic acid (RNA) virus surrogate for SARS-CoV-2 was dried on stainless steel 304 (SS304), Navy Top Coat-painted SS304 (NTC), cardboard, polyurethane, polymethyl methacrylate (PMMA), and acrylonitrile butadiene styrene (ABS) materials at > 8.0 log₁₀ plaque-forming units (PFU) per test coupon. The coupons were then exposed to UV radiation during both laboratory and field testing. Commercial and prototype UV-emitting devices were measured for efficacy: four handheld devices, three room/surface-disinfecting machines, five air disinfection devices, and two larger custom-made machines. UV device dosages ranged from 0.01 to 729 mJ cm⁻². The antiviral efficacy among the different UV devices ranged from no decontamination up to nearly achieving sterilization. Importantly, cardboard required far greater dosage than SS304.

Conclusion: Enormous variability in dosage and efficacy was measured among the different UV devices. Porous materials limit the utility of UV decontamination.

Significance and impact of the study: UV devices have wide variability in dosages, efficacy, hazards, and UV output over time, indicating that each UV device needs independent technical measurement and assessment for product development prior to and during use.

Sterilization effects of UV laser irradiation on Bacillus atrophaeus spore viability, structure, and proteins

Bacillus spores are highly resistant to toxic chemicals and extreme environments. Because some Bacillus species threaten public health, spore inactivation techniques have been intensively investigated. We exposed Bacillus atrophaeus spores to a 266 nm Nd:YVO₄ laser at a laser power of 1 W and various numbers of scans. As a result, the UV laser reduced the viability of Bacillus atrophaeus spores. Although the outer coat of spores remained intact after UV laser irradiation of 720 scans, damage inside the spores was observed. Spore proteins were identified by matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry during the course of UV laser irradiation. Photochemical and photothermal processes are believed to be involved in the UV laser sterilization of Bacillus spores. Our findings suggest that a UV laser is capable of sterilizing Bacillus atrophaeus spores.

Decontamination of soil contaminated at the surface with Bacillus anthracis spores using dry thermal treatment

In the event of a large, aerosol release of Bacillus anthracis spores in a major metropolitan area, soils and other outdoor materials may become contaminated with the biological agent. A study was conducted to assess the in-situ remediation of soil using a dry thermal treatment approach to inactivate a B. anthracis spore surrogate inoculated into soil samples. The study was conducted in two phases, using loam, clay and sand-based soils, as well as biological indicators and spore-inoculated stainless-steel coupons. Initial experiments were performed in an environmental test chamber with temperatures controlled between 80 and 110 °C, with and without added humidity, and with contact times ranging from 4 h to 7 weeks. Tests were then scaled up to assess the thermal inactivation of spores in small soil columns, in which a heating plate set to 141 °C was applied to the soil surface. These column tests were conducted to assess time requirements to inactivate spores as a function of soil depth and soil type. Results from the initial phase of testing showed that increasing the temperature and relative humidity reduced the time requirements to achieve samples in which no surrogate spores were detected. For the test at 80 °C with no added humidity, 49 days were required to achieve soil samples with no spores detected in clay and loam. At 110 °C, 24 h were required to achieve samples in which no spores were detected. In the column tests, no spores were detected at the 2.5 cm depth at four days and at the 5.1 cm depth at 21 days, for two of the three soils. The experiments described in the study demonstrate the feasibility of using dry thermal techniques to decontaminate soils that have been surficially contaminated with B. anthracis spores.

Hot, Humid Air Decontamination of Aircraft Confirmed That High Temperature and High Humidity Are Critical for Inactivation of Infectious, Enveloped Ribonucleic Acid (RNA) Virus

Aims: To develop infectious (live/dead) enveloped virus test indicators and response surface methodology (RSM) models that evaluate survival of an enveloped ribonucleic acid (RNA) virus on contaminated aircraft materials after exposure to hot, humid air (HHA). Methods and Results: Enveloped RNA bacteriophage Phi6 (Φ6) was dried on wiring insulation, aircraft performance coating (APC), polypropylene, and nylon at ≥ 8 log10 plaque-forming units (PFU) test coupon-1. Only 2.4 log10 inactivation was measured on APC at 70°Celsius (°C), 5% relative humidity (RH) after 24 h. In contrast, HHA RSM models showed a 90% probability of a 7 log10 inactivation at ≥63°C, 90% RH after 1 h, and decontamination kinetics were similar across different materials. HHA decontamination of C-130 and C-17 aircraft showed >7 log10 and ≥5.9 log10 inactivation of enveloped virus on 100 and 110 test indicators, respectively, with a 1-h treatment, excluding ramp-up and ramp-down times. Conclusions: Enveloped RNA virus test indicators were successfully developed, lab tested for HHA decontamination, analyzed for RSM, and field-tested in aircraft demonstrations. Significance and Impact of the Study: The utility of HHA decontamination was demonstrated after inactivating enveloped RNA virus on aircraft with a 1-h HHA treatment within aircraft temperature and RH limits.

Biological Validation of a Chemical Effluent Decontamination System

Introduction:

Failure of an existing effluent decontamination system (EDS) prompted the consideration of commercial off-the-shelf solutions for decontamination of containment laboratory waste. A bleach-based chemical EDS was purchased to serve as an interim solution.

Methods:

Studies were conducted in the laboratory to validate inactivation of Bacillus spores with bleach in complex matrices containing organic simulants including fetal bovine serum, humic acid, and animal room sanitation effluent.

Results:

These studies demonstrated effective decontamination of >106 spores at a free chlorine concentration of ≥5700 parts per million with a 2-hour contact time. Translation of these results to biological validation of the bleach-based chemical EDS required some modifications to the system and its operation.

Discussion:

The chemical EDS was validated for the treatment of biosafety levels 3 and 4 waste effluent using laboratory-prepared spore packets along with commercial biological indicators; however, several issues and lessons learned identified during the process of onboarding are also discussed, including bleach product source, method of validation, dechlorination, and treated waste disposal.

The use of ozone gas for the inactivation of Bacillus anthracis and Bacillus subtilis spores on building materials

A study was conducted to assess the efficacy of ozone gas in inactivating spores of both Bacillus anthracis and Bacillus subtilis inoculated onto six building materials (glass, wood, carpet, laminate, galvanized metal, and wallboard paper). Testing conditions consisted of ozone gas concentrations ranging from 7,000-12,000 parts per million (ppm), contact times from 4 to 12 h, and two relative humidity (RH) levels of 75 and 85%. Results showed that increasing the ozone concentration, contact time, and RH generally increased decontamination efficacy. The materials in which the highest decontamination efficacy was achieved for B. anthracis spores were wallboard paper, carpet, and wood with ≥ 6 log10 reduction (LR) occurring with 9,800 ppm ozone, 85% RH, for 6 h. The laminate and galvanized metal materials were generally more difficult to decontaminate, requiring 12,000 ppm ozone, 85% RH, and 9-12 h contact time to achieve ≥6 LR of B. anthracis. Lastly, overall, there were no significant differences in decontamination efficacy between the two species.

DNA Damage Kills Bacterial Spores and Cells Exposed to 222-Nanometer UV Radiation

This study examined the microbicidal activity of 222-nm UV radiation (UV₂₂₂), which is potentially a safer alternative to the 254-nm UV radiation (UV₂₅₄) that is often used for surface decontamination. Spores and/or growing and stationary-phase cells of Bacillus cereus, Bacillus subtilis, Bacillus thuringiensis, Staphylococcus aureus, and Clostridioides difficile and a herpesvirus were all killed or inactivated by UV₂₂₂ and at lower fluences than with UV₂₅₄B. subtilis spores and cells lacking the major DNA repair protein RecA were more sensitive to UV₂₂₂, as were spores lacking their DNA-protective proteins, the α/β-type small, acid-soluble spore proteins. The spore cores' large amount of Ca²⁺-dipicolinic acid (∼25% of the core dry weight) also protected B. subtilis and C. difficile spores against UV₂₂₂, while spores' proteinaceous coat may have given some slight protection against UV₂₂₂ Survivors among B. subtilis spores treated with UV₂₂₂ acquired a large number of mutations, and this radiation generated known mutagenic photoproducts in spore and cell DNA, primarily cyclobutane-type pyrimidine dimers in growing cells and an α-thyminyl-thymine adduct termed the spore photoproduct (SP) in spores. Notably, the loss of a key SP repair protein markedly decreased spore UV₂₂₂ resistance. UV₂₂₂-treated B. subtilis spores germinated relatively normally, and the generation of colonies from these germinated spores was not salt sensitive. The latter two findings suggest that UV₂₂₂ does not kill spores by general protein damage, and thus, the new results are consistent with the notion that DNA damage is responsible for the killing of spores and cells by UV₂₂₂IMPORTANCE Spores of a variety of bacteria are resistant to common decontamination agents, and many of them are major causes of food spoilage and some serious human diseases, including anthrax caused by spores of Bacillus anthracis Consequently, there is an ongoing need for efficient methods for spore eradication, in particular methods that have minimal deleterious effects on people or the environment. UV radiation at 254 nm (UV₂₅₄) is sporicidal and commonly used for surface decontamination but can cause deleterious effects in humans. Recent work, however, suggests that 222-nm UV (UV₂₂₂) may be less harmful to people than UV₂₅₄ yet may still kill bacteria and at lower fluences than UV₂₅₄ The present work has identified the damage by UV₂₂₂ that leads to the killing of growing cells and spores of some bacteria, many of which are human pathogens, and UV₂₂₂ also inactivates a herpesvirus.

Decontamination of Personal Protective Equipment

Exploratory field analyses of the inactivation capacity of disinfectants on contaminated personal protective equipment (PPE) are required to select a suitable surrogate for biohazardous agents like spores of Bacillus anthracis. The objectives of our study were (1) the determination of an appropriate surrogate for the inactivation of spores of B. anthracis with peracetic acid (PAA), and (2) application of optimized inactivation conditions for an effective decontamination of PPE with PAA under field conditions. For inactivation studies, B. anthracis spores from different strains and B. thuringiensis spores were fixed by air drying on carriers prepared from PPE fabric. Time and concentration studies with PAA-based disinfectants revealed that the spores of the B. thuringiensis strain DSM 350 showed an inactivation profile comparable to that of the spores of the B. anthracis strain with the highest stability, implying that B. thuringiensis can serve as an appropriate surrogate. Rapid (3 to 5 minutes) and effective surface decontamination was achieved with 2% PAA/0.2% surfactant. In field studies, PPE contaminated with spores of B. thuringiensis was treated with the disinfectant. Optimizing the decontamination technique revealed that spraying in combination with brushing was effective within 5 minutes of exposure.

Review of Decontamination Techniques for the Inactivation of Bacillus anthracis and Other Spore-Forming Bacteria Associated with Building or Outdoor Materials

Since the intentional release of Bacillus anthracis spores through the U.S. Postal Service in the fall of 2001, research and development related to decontamination for this biological agent have increased substantially. This review synthesizes the advances made relative to B. anthracis spore decontamination science and technology since approximately 2002, referencing the open scientific literature and publicly available, well-documented scientific reports. In the process of conducting this review, scientific knowledge gaps have also been identified. This review focuses primarily on techniques that are commercially available and that could potentially be used in the large-scale decontamination of buildings and other structures, as well as outdoor environments. Since 2002, the body of scientific data related to decontamination and microbial sterilization has grown substantially, especially in terms of quantifying decontamination efficacy as a function of several factors. Specifically, progress has been made in understanding how decontaminant chemistry, the materials the microorganisms are associated with, environmental factors, and microbiological methods quantitatively impact spore inactivation. While advancement has been made in the past 15 years to further the state of the science in the inactivation of bacterial spores in a decontamination scenario, further research is warranted to close the scientific gaps that remain.

Impact of sporicidal fumigation with methyl bromide or methyl iodide on electronic equipment

The effect of sporicidal fumigation with methyl bromide or methyl iodide on the functionality of valuable electronic equipment was evaluated using desktop computers as surrogates under target conditions of 200-250 mg/L fumigant for 48 h at 24-30 °C and 75-85% RH. Methyl iodide fumigation damaged light-emitting diodes and optical films in computer displays that were powered-on during fumigation. After five months of post-fumigation operation, five out of six methyl-bromide-fumigated and all six methyl-iodide-fumigated DVD ± RW optical drives failed. Deterioration of rubber spacers critical to maintaining correct disc geometry caused the failure. Metal coupons, included to measure corrosion, showed no significant differences in weight gain between control and fumigation conditions. Relative humidity sensors exhibited a substantial and sometimes irreversible reduction in sensitivity during and after methyl iodide fumigation. Methyl bromide and methyl iodide can cause damage to electronic equipment, but damage seems to be limited to organic materials rather than corrosion of metal surfaces.

Genetic Fusion of an Anti-BclA Single-Domain Antibody with Beta Galactosidase

The Bacillus collagen-like protein of anthracis (BclA), found in Bacillus anthracis spores, is an attractive target for immunoassays. Previously, using phage display we had selected llama-derived single-domain antibodies that bound to B. anthracis spore proteins including BclA. Single-domain antibodies (sdAbs), the recombinantly expressed heavy domains from the unique heavy-chain-only antibodies found in camelids, provide stable and well-expressed binding elements with excellent affinity. In addition, sdAbs offer the important advantage that they can be tailored for specific applications through protein engineering. A fusion of a BclA targeting sdAb with the enzyme Beta galactosidase (β-gal) would enable highly sensitive immunoassays with no need for a secondary reagent. First, we evaluated five anti-BclA sdAbs, including four that had been previously identified but not characterized. Each was tested to determine its binding affinity, melting temperature, producibility, and ability to function as both capture and reporter in sandwich assays for BclA. The sdAb with the best combination of properties was constructed as a fusion with β-gal and shown to enable sensitive detection. This fusion has the potential to be incorporated into highly sensitive assays for the detection of anthrax spores.

A Standard Method To Inactivate Bacillus anthracis Spores to Sterility via Gamma Irradiation

In 2015, a laboratory of the United States Department of Defense (DoD) inadvertently shipped preparations of gamma-irradiated spores of Bacillus anthracis that contained live spores. In response, a systematic evidence-based method for preparing, concentrating, irradiating, and verifying the inactivation of spore materials was developed. We demonstrate the consistency of spore preparations across multiple biological replicates and show that two different DoD institutions independently obtained comparable dose-inactivation curves for a monodisperse suspension of B. anthracis spores containing 3 × 10¹⁰ CFU. Spore preparations from three different institutions and three strain backgrounds yielded similar decimal reduction (D₁₀) values and irradiation doses required to ensure sterility (D_SAL) to the point at which the probability of detecting a viable spore is 10^-6 Furthermore, spores of a genetically tagged strain of B. anthracis strain Sterne were used to show that high densities of dead spores suppress the recovery of viable spores. Together, we present an integrated method for preparing, irradiating, and verifying the inactivation of spores of B. anthracis for use as standard reagents for testing and evaluating detection and diagnostic devices and techniques.IMPORTANCE The inadvertent shipment by a U.S. Department of Defense (DoD) laboratory of live Bacillus anthracis (anthrax) spores to U.S. and international destinations revealed the need to standardize inactivation methods for materials derived from biological select agents and toxins (BSAT) and for the development of evidence-based methods to prevent the recurrence of such an event. Following a retrospective analysis of the procedures previously employed to generate inactivated B. anthracis spores, a study was commissioned by the DoD to provide data required to support the production of inactivated spores for the biodefense community. The results of this work are presented in this publication, which details the method by which spores can be prepared, irradiated, and tested, such that the chance of finding residual living spores in any given preparation is 1/1,000,000. These irradiated spores are used to test equipment and methods for the detection of agents of biological warfare and bioterrorism.

Surrogate strains of human pathogens for field release

Surrogate microorganisms, in short surrogates, are an essential part of pathogen research. Compared to surrogates used in controlled laboratory environments, surrogates for field release are restricted by concerns about human and environmental safety. For field research of food-borne pathogens, strains of an attenuated pathogen or strains of genetically close non-pathogenic species have been used as surrogates. Genetic modification is usually performed to attenuate virulence, through for examples deletion of genes of virulence and transcriptional regulators and removal of virulence plasmids, and to facilitate detection and monitoring through observing antibiotic resistance, fluorescence, and bioluminescence. For field research of a biological warfare agent Bacillus anthracis, strains of genetically close non-pathogenic species or strains of genetically distant non-pathogenic species have been used, mostly without any genetic modification. Recently, we constructed strains of Bacillus thuringiensis as surrogates for B. anthracis, demonstrating that strain engineering could significantly enhance the utility of surrogates, and that the application of a simple genetic circuit could significantly impact surrogate safety. Thus far, enormous potential of biotechnology has not been exploited enough due to safety concerns regarding the field release of genetically engineered microorganisms. However, synthetic biology is rapidly developing, providing new concepts for biocontainment as well as ingenious genetic circuits and devices, which should be applied in future research of field-use surrogates.

Aerosol and Surface Deposition Characteristics of Two Surrogates for Bacillus anthracis Spores

Spores of an acrystalliferous derivative of Bacillus thuringiensis subsp. kurstaki, termed Btcry-, are morphologically, aerodynamically, and structurally indistinguishable from Bacillus anthracis spores. Btcry- spores were dispersed in a large, open-ended barn together with spores of Bacillus atrophaeus subsp. globigii, a historically used surrogate for Bacillus anthracis Spore suspensions (2 × 10¹² CFU each of B. atrophaeus subsp. globigii and Btcry-) were aerosolized in each of five spray events using a backpack misting device incorporating an air blower; a wind of 4.9 to 7.6 m s^-1 was also flowing through the barn in the same direction. Filter air samplers were situated throughout the barn to assess the aerosol density of the spores during each release. Trays filled with a surfactant in aqueous buffer were placed on the floor near the filter samplers to assess spore deposition. Spores were also recovered from arrays of solid surfaces (concrete, aluminum, and plywood) that had been laid on the floor and set up as a wall at the end of the barn. B. atrophaeus subsp. globigii spores were found to remain airborne for significantly longer periods, and to be deposited on horizontal surfaces at lower densities, than Btcry- spores, particularly near the spray source. There was a 6-fold-higher deposition of Btcry- spores than of B. atrophaeus subsp. globigii spores on vertical surfaces relative to the surrounding airborne density. This work is relevant for selecting the best B. anthracis surrogate for the prediction of human exposure, hazard assessment, and hazard management following a malicious release of B. anthracis IMPORTANCE: There is concern that pathogenic bacteria could be maliciously disseminated in the air to cause human infection and disruption of normal life. The threat from spore-forming organisms, such as the causative agent of anthrax, is particularly serious. In order to assess the extent of this risk, it is important to have a surrogate organism that can be used to replicate the dispersal characteristics of the threat agent accurately. This work compares the aerosol dispersal and deposition behaviors of the surrogates Btcry- and B. atrophaeus subsp. globigii Btcry- spores remained in the air for a shorter time, and were markedly more likely to adhere to vertical surfaces, than B. atrophaeus subsp. globigii spores.