Identifying experimental surrogates for Bacillus anthracis spores: a review

CRISPR-Cas9-mediated barcode insertion into Bacillus thuringiensis for surrogate tracking

The use of surrogate organisms can enable researchers to safely conduct research on pathogens and in a broader set of conditions. Being able to differentiate between the surrogates used in the experiments and background contamination as well as between different experiments will further improve research efforts. One effective approach is to introduce unique genetic barcodes into the surrogate genome and track their presence using the quantitative polymerase chain reaction (qPCR). In this report, we utilized the CRISPR-Cas9 methodology, which employs a single plasmid and a transformation step to insert five distinct barcodes into Bacillus thuringiensis, a well-established surrogate for Bacillus anthracis when Risk Group 1 organisms are needed. We subsequently developed qPCR assays for barcode detection and successfully demonstrated the stability of the barcodes within the genome through five cycles of sporulation and germination. Additionally, we conducted whole-genome sequencing on these modified strains and analyzed 187 potential Cas9 off-target sites. We found no correlation between the mutations observed in the engineered strains and the predicted off-target sites, suggesting this genome engineering strategy did not directly result in off-target mutations in the genome. This simple approach has the potential to streamline the creation of barcoded B. thuringiensis strains for use in future studies on surrogate genomes.

IMPORTANCE

The use of Bacillus anthracis as a biothreat agent poses significant challenges for public health and national security. Bacillus anthracis surrogates, like Bacillus thuringiensis, are invaluable tools for safely understanding Bacillus anthracis properties without the safety concerns that would arise from using a virulent strain of Bacillus anthracis. We report a simple method for barcode insertion into Bacillus thuringiensis using the CRISPR-Cas9 methodology and subsequent tracking by quantitative polymerase chain reaction (qPCR). Moreover, whole-genome sequencing data and CRISPR-Cas9 off-target analyses in Bacillus thuringiensis suggest that this gene-editing method did not directly cause unwanted mutations in the genome. This study should assist in the facile development of barcoded Bacillus thuringiensis surrogate strains, among other biotechnological applications in Bacillus species.

Evaluation of sponge wipe surface sampling for collection of potential surrogates for non-spore-forming bioterrorism agents

AIM

Evaluate the efficacy of sponge wipe sampling at recovering potential bacterial surrogates for Category A and B non-spore-forming bacterial bioterrorism agents from hard, nonporous surfaces.

METHODS

A literature survey identified seven nonpathogenic bacteria as potential surrogates for selected Category A and B non-spore-forming bacterial agents. Small (2 × 4 cm) and large (35.6 × 35.6 cm) coupons made from either stainless steel, plastic, or glass, were inoculated and utilized to assess persistence and surface sampling efficiency, respectively. Three commercially available premoistened sponge wipes (3M™, Sani-Stick®, and Solar-Cult®) were evaluated.

RESULTS

Mean recoveries from persistence testing indicated that three microorganisms (Yersinia ruckeri, Escherichia coli, and Serratia marcescens) demonstrated sufficient persistence across all tested material types. Sampling of large inoculated (≥107 CFU per sample) coupons resulted in mean recoveries ranging from 6.6 to 3.4 Log10 CFU per sample. Mean recoveries for the Solar-Cult®, 3M™ sponge wipes, and Sani-Sticks® across all test organisms and all material types were ≥5.7, ≥3.7, and ≥3.4 Log10 CFU per sample, respectively. Mean recoveries for glass, stainless steel, and ABS plastic across all test organisms and all sponge types were ≥3.8, ≥3.7, and ≥3.4 Log10 CFU per sample, respectively.

CONCLUSIONS

Recovery results suggest that sponge wipe sampling can effectively be used to recover non-spore-forming bacterial cells from hard, nonporous surfaces such as stainless steel, ABS plastic, and glass.

The potential to manage releases of Bacillus anthracis using bioretention and a high flow media filter: Results of simulated runoff testing with tracer spores Bacillus globigii

The threat of bioterrorism has spurred research on the decontamination and containment of different agents. Anthrax [causative agent Bacillus anthracis (Ba)] is a disease that can lead to severe infections within human and animals, particularly when inhaled. This research investigated the use of spore-contaminated simulated runoff events into stormwater control measures (SCMs), which are designed to retain and improve the quality of runoff and may have the potential to filter and contain the spores. In this study, the effectiveness of a bioretention cell (BRC) and high flow media filter (HFMF) in Huron, Ohio, were evaluated for removal of Bacillus globigii (Bg) spores (a harmless cognate of Ba). Three 4-8 mm simulated runoff events were created for each SCM using a fire hydrant and Bg spores were injected into the runoff upstream of the SCM inlets. The BRC significantly (p < 0.001) outperformed the HFMF in reducing Bg concentrations and loads, with an average load reduction of 1.9 log (∼99% reduction) compared to 0.4 (∼60% reduction), respectively. A probable critical design factor leading to these differences was the infiltration rate of the media and subsequent retention time within the filters, which was supported by similar disparities in suspended solids reductions. Differences in spore removal may also have been due to particle size distribution of the HFMF, which was more gravelly than the bioretention cell. At 3 and 6 months after the-simulated runoff tests, soil samples taken from both SCMs, yielding detectable Bg spores within the top 15 cm of media, with increased spore concentrations where ponding occurred for longer durations during the tests. This suggests that forebays and areas near inlets may be hotspots for spore cleanup in a real-world bioterrorism incident.

Characterizing Bacillus globigii as a Bacillus anthracis surrogate for wastewater treatment studies and bioaerosol emissions

This study characterized Bacillus globigii (BG) as a Bacillus anthracis Sterne (BAS) surrogate for wastewater treatment-related studies of UV inactivation, adsorption onto powdered activated carbon (PAC), and bioaerosol emission. The inactivation of BG was faster than that of BAS in DI water (pseudo first-order rate constants of 0.065 and 0.016 min-1 respectively) and in PBS solution (0.030 and 0.005 min-1 respectively). BG was also removed more quickly than BAS by PAC adsorption in DI (0.07 and 0.05 min-1 respectively) and in PBS (0.09 and 0.04 min-1 respectively). In DI, BG aggregated more (P < 0.05) than BAS when the pH was 7 or greater but there were no statistically significant differences in NaCl solution. Spore aggregation was also studied with extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) models. Less than 1% of all spores were released as bioaerosols, and there was no significant difference (P > 0.05) in emission between BG and BAS. To the author's knowledge, this study is the first to demonstrate that BG is a suitable surrogate for BAS for bioaerosol emissions, but a poor surrogate for both UV inactivation and PAC adsorption. These results can be used to understand the ability of BAS to act as a surrogate for BA Ames because of its genetic and morphological similarities with BAS.

Anthrax revisited: how assessing the unpredictable can improve biosecurity

B. anthracis is one of the most often weaponized pathogens. States had it in their bioweapons programs and criminals and terrorists have used or attempted to use it. This study is motivated by the narrative that emerging and developing technologies today contribute to the amplification of danger through greater easiness, accessibility and affordability of steps in the making of an anthrax weapon. As states would have way better preconditions if they would decide for an offensive bioweapons program, we focus on bioterrorism. This paper analyzes and assesses the possible bioterrorism threat arising from advances in synthetic biology, genome editing, information availability, and other emerging, and converging sciences and enabling technologies. Methodologically we apply foresight methods to encourage the analysis of contemporary technological advances. We have developed a conceptual six-step foresight science framework approach. It represents a synthesis of various foresight methodologies including literature review, elements of horizon scanning, trend impact analysis, red team exercise, and free flow open-ended discussions. Our results show a significant shift in the threat landscape. Increasing affordability, widespread distribution, efficiency, as well as ease of use of DNA synthesis, and rapid advances in genome-editing and synthetic genomic technologies lead to an ever-growing number and types of actors who could potentially weaponize B. anthracis. Understanding the current and future capabilities of these technologies and their potential for misuse critically shapes the current and future threat landscape and underlines the necessary adaptation of biosecurity measures in the spheres of multi-level political decision making and in the science community.

Optimal Fast Integral Decontamination of Bacillus thuringiensis Aerosols and Fast Disinfection of Contaminated Surfaces

Aerosolized anthrax (Bacillus anthracis) spores are of extreme health concern and can remain airborne for hours and contaminate all kinds of surfaces, constituting reservoirs from which resuspension is easily produced. The assessment of decontamination techniques must therefore consider both air and surfaces. In the present study, several kinds of disinfecting fogs were experimentally tested against Bacillus thuringiensis spores, which served as a surrogate for Bacillus anthracis, both as aerosols released into the air and spread on porous and non-porous surfaces with different positions and orientations. This technology removed Bacillus thuringiensis spores from the air in 20 min with just a 1 min application of fog. The dynamics and characteristics of the fog, related to aerosol and surface interactions, proved to be critical for optimal performance and decontamination. An optimal configuration could provide effective disinfection even on indirectly reached surfaces. In all cases, 8% hydrogen peroxide (H₂O₂) provided a higher disinfection rate than 2% glutaraldehyde.

Development of Methods for Specific Capture of Biological Targets on Aluminum Substrates: Application to Bacillus subtilis Spore Detection as a Model for Anthrax

Many (if not most) biosensors rely on functional silane coatings as a first step toward covalent immobilization of specific capture molecules. While methods for silanization of silica (SiO2) surfaces are very well developed, less has been done to develop and characterize silanization methods for alternative substrates, such as alumina (Al2O3). In particular, the behavior of Al2O3 coatings grown on aluminum under ambient conditions has not been studied. To address this issue, we have tested solution-phase deposition of two silanes on Al2O3 (3-aminopropyl triethoxysilane and 3-triethoxysilyl)propylsuccinic anhydride) and their applicability to analyte-specific biosensing. Contact angle measurements and imaging via Scanning Electron Microsopy (SEM) were employed to characterize surfaces. We find that 3-aminopropyl triethoxysilane produces well-behaved films and demonstrate that this surface can undergo further reaction with glutaraldehyde followed by an anti-Bacillus subtilis antibody to yield functionalized Al2O3 surfaces capable of specific capture of B. subtilis spores (a model of B. anthracis, the causative organism of Anthrax). In contrast, 3-triethoxysilyl)propylsuccinic anhydride did not behave well with Al/Al2O3 under the reaction conditions tested. In addition to providing specific protocols for Al/Al2O3 functionalization, this work highlights the importance of surface chemistry assessment in the development of new sensors.

Influence of wash aids on Bacillus spore removal from an asphalt parking lot using two spray-based washing methods

AIMS

The goal of this study was to measure the removal efficacy of Bacillus atrophaeus spores from a parking lot using spray-based washing methods (a pressure washer and a garden hose) and wash aids. B. atrophaeus is a commonly used nonpathogenic surrogate for B. anthracis, the causative agent of anthrax and a deadly bioterrorism agent that would cause major disruptions and damage to public health should it be disseminated over an urban area.

METHODS AND RESULTS

Five wash aids (1 mM sodium chloride, an Instant Ocean® seawater solution, 0.01% Tween 20, 0.01% sodium dodecyl sulfate, and unamended tap water) were used along with two different spray sequences in this study. Across all treatment conditions, 3.7-6.4 log₁₀  colony forming unit were recovered in the runoff water, and 0.15%-23% of spores were removed from the surface of the parking lot.

CONCLUSIONS

Pressure washing removed more spores than the garden hose, and for both types of washing methods, the first pass removed more spores than the subsequent passes. The Instant Ocean and Tween 20 wash aids were found to significantly increase the percentage of spore removal when using the pressure washer, but the overall increase was only 1%-2% compared to the tap water alone.

SIGNIFICANCE AND IMPACT OF STUDY

This study provides public officials and emergency responders with baseline spore physical removal information for situations where a corrosive disinfectant might have a negative impact on the environment and washing is being considered as an alternative remediation approach.

Strategies for capturing Bacillus thuringiensis spores on surfaces of (001) GaAs-based biosensors

Bacillus thuringiensis (Bt) is used as a bioinsecticide since it effectively kills insect larvae. Bt is also genetically similar to Bacillus cereus (Bc), a well recognized foodborne human pathogen; they are both members of the Bacillus cereus group (BC group). Although approved Bt bioinsecticide products have been confirmed to be non-pathogenic to humans, close monitoring of Bt during dissemination is important for cost considerations and to limit impact on biodiversity towards nontarget organisms. As such, developing rapid, sensitive, and specific tools for quantitative detection of Bt spores during and following spray operations is highly desirable. The goals of this study were to investigate commercially available detection reagents for sensitivity and selectivity in detecting Bt spores, and then functionalize a surface of (001) GaAs used in photonic biosensing. To achieve these goals, we (1) screened commercial antibodies for their capacity to bind recombinant proteins from Bt spores, (2) screened antibodies and aptamers for their sensitivity and selectivity against Bt spores, and (3) tested the efficiency of selected antibodies and aptamers in capturing Bt spores on the surface of functionalized GaAs biochips. Seven genes encoding Bt spore proteins were cloned and expressed in Escherichia coli. The binding of each purified spore antigen was tested by commercially available polyclonal and monoclonal antibodies claimed to exclusively target spores. Of the seven targets, Bacillus collagen-like protein A, was the most abundant protein on Bt spores and demonstrated the strongest binding affinity to all test antibodies. The commercial antibodies (Abs) were also tested for specificity to BC Group versus non-BC Group spores. Three of six commercial antibodies showed selectivity to Bt spores, with recombinant Abs providing the most robust lower range of detection (10² to 6 × 10³ spores/mL). The sensitivity and selectivity of three published DNA aptamer sequences demonstrated a wide range of detection sensitivity for Bt spores. Two of the three test aptamers also showed reasonable selectivity towards Bt spores while the third demonstrated reactivity to non-BC Group B. megaterium and B. subtilis. Of the reagents tested, a thiolated aptamer and llama recombinant Ab showed highest Bt spore capture efficiency as measured by spore coverage of the GaAs surface. These results confirm that the selected aptamer and llama rAb can be considered strong candidates for the development of GaAs-based biosensing devices.

pLS20 is the archetype of a new family of conjugative plasmids harboured by Bacillus species

Conjugation plays important roles in genome plasticity, adaptation and evolution but is also the major horizontal gene-transfer route responsible for spreading toxin, virulence and antibiotic resistance genes. A better understanding of the conjugation process is required for developing drugs and strategies to impede the conjugation-mediated spread of these genes. So far, only a limited number of conjugative elements have been studied. For most of them, it is not known whether they represent a group of conjugative elements, nor about their distribution patterns. Here we show that pLS20 from the Gram-positive bacterium Bacillus subtilis is the prototype conjugative plasmid of a family of at least 35 members that can be divided into four clades, and which are harboured by different Bacillus species found in different global locations and environmental niches. Analyses of their phylogenetic relationship and their conjugation operons have expanded our understanding of a family of conjugative plasmids of Gram-positive origin.

Real-World Ethical Dilemmas in Laboratory Safety for Microbiology Under-Resourced and Outreach Teaching

With modernization of safety standards for microbiology outreach teaching laboratories, ethical challenges arise in teaching microbiology for the public good without short-changing students in under-resourced situations, or when institutional support is subpar. Still, educators want students to engage using applied skills for inquiry, research-based microbial learning activities – safely. Following several United States microbial outbreaks, federal investigation traced sources back to teaching laboratories. Policy discussions ensued. The American Society for Microbiology (ASM) Task Force provides recommended but not mandated guidelines; however, guidelines are not amenable by all. Here, a real-world, ethical scenario of a university-level outreach microbiology laboratory course hosted at several locations provides context for under-resourced challenges in safety compliance. In this example of biomedical and public health ethical considerations, upper administration puts the onus on instructors to assure safe labs for their students and the general public. Temporarily hired instructors without curriculum or sufficient institutional support are put in precarious positions with often egregious practices to get the job done. This scenario is examined with different public health ethical frameworks and principles: non-maleficence, beneficence, health maximization, efficiency of policy regulations, respect for institutional and instructor autonomy, justice, and proportionality balancing stakeholder concerns. Sample curricular strategies are employed to mitigate these challenges. Taking a utilitarianism framework of the greatest good for the most benefit, this paper advocates for social justice supporting access to education as a moral duty. Administrations should ensure instructors are supported sufficiently to provide safe, authentic learning experiences. Solutions for under-resourced outreach teaching are needed for public trust.

barCoder: a tool to generate unique, orthogonal genetic tags for qPCR detection

BACKGROUND

Tracking dispersal of microbial populations in the environment requires specific detection methods that discriminate between the target strain and all potential natural and artificial interferents, including previously utilized tester strains. Recent work has shown that genomic insertion of short identification tags, called "barcodes" here, allows detection of chromosomally tagged strains by real-time PCR. Manual design of these barcodes is feasible for small sets, but expansion of the technique to larger pools of distinct and well-functioning assays would be significantly aided by software-guided design.

RESULTS

Here we introduce barCoder, a bioinformatics tool that facilitates the process of creating sets of uniquely identifiable barcoded strains. barCoder utilizes the genomic sequence of the target strain and a set of user-specified PCR parameters to generate a list of suggested barcode "modules" that consist of binding sites for primers and probes, and appropriate spacer sequences. Each module is designed to yield optimal PCR amplification and unique identification. Optimal amplification includes metrics such as ideal melting temperature and G+C content, appropriate spacing, and minimal stem-loop formation; unique identification includes low BLAST hits against the target organism, previously generated barcode modules, and databases (such as NCBI). We tested the ability of our algorithm to suggest appropriate barcodes by generating 12 modules for Bacillus thuringiensis serovar kurstaki-a simulant for the potential biowarfare agent Bacillus anthracis-and three each for other potential target organisms with variable G+C content. Real-time PCR detection assays directed at barcodes were specific and yielded minimal cross-reactivity with a panel of near-neighbor and potential contaminant materials.

CONCLUSIONS

The barCoder algorithm facilitates the generation of synthetically barcoded biological simulants by (a) eliminating the task of creating modules by hand, (b) minimizing optimization of PCR assays, and (c) reducing effort wasted on non-unique barcode modules.

Rainfall Washoff of Spores From Concrete and Asphalt Surfaces

After a biological terrorist attack, understanding the migration of agents such as Bacillus anthracis is critical due to their deadly nature. This is important in urban settings with higher likelihood of human exposure and a large fraction of impervious materials contributing to pollutant washoff. The study goals were to understand the removal of spores from urban surfaces under different rainfall conditions, to compare washoff of two B. anthracis surrogate spores, and to compare two empirical fits for the first flush of spores from small areas. Concrete and asphalt were inoculated with either Bacillus atrophaeus or Bacillus thuringiensis kurstaki spores and exposed to simulated rainfall. The study assessed goodness-of-fit for the Storm Water Management Model (SWMM)'s exponential washoff function compared to an alternative two-stage exponential function. The highest average washoff of spores was 15% for an hour-long experiment. Spore washoff was not significantly different for the two spore types, but there were significant differences in washoff from asphalt versus concrete with more occurring from asphalt. Average kinetic energy of the storm event impacted washoff from asphalt, but not concrete. The two-stage function had a better goodness-of-fit than the SWMM exponential function. As such, emergency responders should be aware that the spread of contamination is impacted by the droplet characteristics of the storm event and the surface material type in the contaminated area; modelers should be aware that different data-fitting approaches may be more appropriate for first-flush calculations of small washoff areas than those used for continuous long-term simulation of large subcatchments.

Clustering, morphology, and treatment resistance of Bacillus globigii spores recovered from a pilot-scale activated sludge system

This study examines the organization and morphology of Bacillus globigii (BG) spores, a common surrogate for Bacillus anthracis, which were seeded and then recovered at various times from several points within a conventional, pilot-scale activated sludge system. Recovered BG spores were enumerated, microscopically examined, and tested for resistance to chemical (i.e. 5% H₂O₂ for 8 min), thermal (80 °C for 30 min), and ultraviolet light (8 W, 254 nm UV for 1 min) inactivation. Spores exposed to activated sludge germinated, sporulated, and exhibited unique multilayer clustering patterns and statistically significant changes (p < 0.005) in dimensional morphology. Spores collected in the later experimental stages (i.e., during weeks 6 and 7) were significantly more resistant (p ≤ 0.05) to inactivation than those collected on the first day of testing. These results have direct consequences for sludge treatment requirements at wastewater treatment plants that receive spore-containing waste streams.

Laboratory results and mathematical modeling of spore surface interactions in stormwater runoff

Development of numerical models to predict stormwater-mediated transport of pathogenic spores in the environment depends on an understanding of adhesion forces that dictate detachment after rain events. Zeta potential values were measured in the laboratory for Bacillus globigii and Bacillus thuringiensis kurstaki, two common surrogates used to represent Bacillus anthracis, in synthetic baseline ultrapure water and laboratory prepared stormwater. Zeta potential curves were also determined for materials representative of urban infrastructure (concrete and asphalt). These data were used to predict the interaction energy between the spores and urban materials using Derjaguin-Landau-Verwey-Overbeek (DLVO) modeling. B. globigii and B. thuringiensis kurstaki sourced from Yakibou Inc., were found to have similar zeta potential curves, whereas spores sourced from the U.S. military's Dugway laboratory were found to diverge. In the ultrapure water, the modeling results use the laboratory data to demonstrate that the energy barriers between the spores and the urban materials were tunable through compression of the electrical double layer of the spores via changes of ionic strength and pH of the water. In the runoff water, charge neutralization dominated surface processes. The cations, metals, and natural organic matter (NOM) in the runoff water contributed to equalizing the zeta potential values for Dugway B. globigii and B. thuringiensis kurstaki, and drastically modified the surface of the concrete and asphalt. All DLVO energy curves using the runoff water were repulsive. The highest energy barrier predicted in this study was for Dugway B. globigii spores interacting with a concrete surface in runoff water, suggesting that this would be the most challenging combination to detach through water-based decontamination.

Repurposing Clinically Approved Drugs for the Treatment of Bacillus cereus, a Surrogate for Bacillus anthracis

Of the numerous infectious diseases afflicting humans, anthrax disease, caused by Bacillus anthracis, poses a major threat in its virulence and lack of effective treatment. The currently lacking standards of care, as well as the lengthy drug approval process, demonstrate the pressing demand for treatment for B. anthracis infections. The present study screened 1586 clinically approved drugs in an attempt to identify repurposable compounds against B. cereus, a relative strain that shares many physical and genetic characteristics with B. anthracis. Our study yielded five drugs that successfully inhibited B. cereus growth: dichlorophen, oxiconazole, suloctidil, bithionol, and hexestrol. These drugs exhibited varying levels of efficacy in broad-spectrum experiments against several Gram-positive and Gram-negative bacterial strains, with hexestrol showing the greatest inhibition across all tested strains. Through tests for the efficacy of each drug on B. cereus, bithionol was the single most potent compound on both solid and liquid media and exhibited even greater eradication of B. cereus in combination with suloctidil on solid agar. This multifaceted in vitro study of approved drugs demonstrates the potential to repurpose these drugs as treatments for anthrax disease in a time-efficient manner to address a global health need.

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.

Inactivation of bacterial and fungal spores by UV irradiation and gaseous iodine treatment applied to air handling filters

Exposure to viable bacterial and fungal spores re-aerosolized from air handling filters may create a major health risk. Assessing and controlling this exposure have been of interest to the bio-defense and indoor air quality communities. Methods are being developed for inactivating stress-resistant viable microorganisms collected on ventilation filters. Here we investigated the inactivation of spores of Bacillus thuringiensis var. kurstaki (Btk), a recognized simulant for B. antracis, and Aspergillus fumigatus, a common opportunistic pathogen used as an indicator for indoor air quality. The viability change was measured on filters treated with ultraviolet (UV) irradiation and gaseous iodine. The spores were collected on high-efficiency particulate air (HEPA) and non-HEPA filters, both flattened for testing purposes to represent "surface" filters. A mixed cellulose ester (MCE) membrane filter was also tested as a reference. Additionally, a commercial HEPA unit with a deep-bed (non-flattened) filter was tested. Combined treatments of Btk spores with UV and iodine on MCE filter produced a synergistic inactivation effect. No similar synergy was observed for A. fumigatus. For spores collected on an MCE filter, the inactivation effect was about an order of magnitude greater for Btk compared to A. fumigatus. The filter type was found to be an important factor affecting the inactivation of Btk spores while it was not as influential for A. fumigatus. Overall, the combined effect of UV irradiation and gaseous iodine on viable bacterial and fungal spores collected on flat filters was found to be potent. The benefit of either simultaneous or sequential treatment was much lower for Btk spores embedded inside the deep-bed (non-flattened) HEPA filter, but for A. fumigatus the inactivation on flattened and non-flattened HEPA filters was comparable. For both species, applying UV first and gaseous iodine second produced significantly higher inactivation than when applying them simultaneously or in an opposite sequence.

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.

Evaluating the long-term persistence of Bacillus spores on common surfaces

Bacillus spores resist inactivation, but the extent of their persistence on common surfaces is unclear. This work addresses knowledge gaps regarding biothreat agents in the environment to reduce uncertainty in risk assessment models. Studies were conducted to investigate the long-term inactivation of Bacillus anthracis and three commonly used surrogate organisms - B. cereus, B. atrophaeus and B. thuringiensis on three materials: laminate countertop, stainless steel and polystyrene Petri dishes. Viable spores were measured at 1, 30, 90, 196, 304 and 1038 days. Twelve different persistence models were fit to the data using maximum likelihood estimation and compared. The study found that (1) spore inactivation was not log-linear, as commonly modelled; (2) B. thuringiensis counts increased at 24 h on all materials, followed by a subsequent decline; (3) several experiments showed evidence of a 'U' shape, with spore counts apparently decreasing and then increasing between 1 and 304 days; (4) spores on polystyrene showed little inactivation; and (5) the maximum inactivation of 56% was observed for B. atrophaeus spores on steel at 196 days. Over the range of surfaces, time durations and conditions (humidity controlled vs. uncontrolled) examined, B. thuringiensis most closely matched the behaviour of B. anthracis.

Comparison of false-negative rates and limits of detection following macrofoam-swab sampling of Bacillus anthracis surrogates via Rapid Viability PCR and plate culture

AIMS

We evaluated the effects of Bacillus anthracis surrogates, low surface concentrations, surface materials and assay methods on false-negative rate (FNR) and limit of detection (LOD₉₅ ) for recovering Bacillus spores using a macrofoam-swab sampling procedure.

METHODS AND RESULTS

Bacillus anthracis Sterne or Bacillus atrophaeus Nakamura spores were deposited over a range of low target concentrations (2-500 per coupon) onto glass, stainless steel, vinyl tile and plastic. Samples were assayed using a modified Rapid Viability-PCR (mRV-PCR) method and the traditional plate culture method to obtain FNR and LOD₉₅ results.

CONCLUSIONS

Mean FNRs tended to be lower for mRV-PCR compared to culturing, and increased as spore concentration decreased for all surface materials. Surface material, but not B. anthracis surrogate, influenced FNRs with the mRV-PCR method. The mRV-PCR LOD₉₅ was lowest for glass and highest for vinyl tile. LOD₉₅ values overall were lower for mRV-PCR than for the culture method.

SIGNIFICANCE AND IMPACT OF STUDY

This study adds to the limited data on FNR and LOD₉₅ for mRV-PCR and culturing methods with low concentrations of B. anthracis sampled from various surface materials by the CDC macrofoam-swab method. These are key inputs for planning characterization and clearance studies for low contamination levels of B. anthracis.

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.

Selection of Surrogate Bacteria for Use in Food Safety Challenge Studies: A Review

Nonpathogenic surrogate bacteria are prevalently used in a variety of food challenge studies in place of foodborne pathogens such as Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, and Clostridium botulinum because of safety and sanitary concerns. Surrogate bacteria should have growth characteristics and/or inactivation kinetics similar to those of target pathogens under given conditions in challenge studies. It is of great importance to carefully select and validate potential surrogate bacteria when verifying microbial inactivation processes. A validated surrogate responds similar to the targeted pathogen when tested for inactivation kinetics, growth parameters, or survivability under given conditions in agreement with appropriate statistical analyses. However, a considerable number of food studies involving putative surrogate bacteria lack convincing validation sources or adequate validation processes. Most of the validation information for surrogates in these studies is anecdotal and has been collected from previous publications but may not be sufficient for given conditions in the study at hand. This review is limited to an overview of select studies and discussion of the general criteria and approaches for selecting potential surrogate bacteria under given conditions. The review also includes a list of documented bacterial pathogen surrogates and their corresponding food products and treatments to provide guidance for future studies.

Evaluation of personal inhalable aerosol samplers with different filters for use during anthrax responses

Risk of inhalation exposure to viable Bacillus anthracis (B. anthracis) spores has primarily been assessed using short-term, stationary sampling methods which may not accurately characterize the concentration of inhalable-sized spores reaching a person's breathing zone. While a variety of aerosol sampling methods have been utilized during previous anthrax responses, no consensus has yet been established for personal air sampling. The goal of this study was to determine the best sampler-filter combination(s) for the collection and extraction of B. anthracis spores. The study was designed to (1) evaluate the performance of four filter types (one mixed cellulose ester, MCE (pore size = 3 µm), two polytetrafluoroethylene, PTFE (1 and 3 µm), and one polycarbonate, PC (3 µm)); and (2) evaluate the best performing filters in two commercially available inhalable aerosol samplers (IOM and Button). Bacillus thuringiensis kurstaki [Bt(k)], a simulant for B. anthracis, served as the aerosol challenge. The filters were assessed based on criteria such as ability to maintain low pressure drop over an extended sampling period, filter integrity under various environmental conditions, spore collection and extraction efficiencies, ease of loading and unloading the filters into the samplers, cost, and availability. Three of the four tested collection filters-except MCE-were found suitable for efficient collection and recovery of Bt(k) spores sampled from dry and humid as well as dusty and clean air environments for up to 8 hr. The PC (3 µm) filter was identified as the best performing filter in this study. The PTFE (3 µm) demonstrated a comparable performance, but it is more expensive. Slightly higher concentrations were measured with the IOM inhalable sampler which is the preferred sampler's performance criterion when detecting a highly pathogenic agent with no established "safe" inhalation exposure level. Additional studies are needed to address the effects of environmental conditions and spore concentration. The data obtained in this investigation are crucial for future efforts on the development and optimization of a method for assessing inhalation exposure to B. anthracis.

Holographic deep learning for rapid optical screening of anthrax spores

Establishing early warning systems for anthrax attacks is crucial in biodefense. Despite numerous studies for decades, the limited sensitivity of conventional biochemical methods essentially requires preprocessing steps and thus has limitations to be used in realistic settings of biological warfare. We present an optical method for rapid and label-free screening of Bacillus anthracis spores through the synergistic application of holographic microscopy and deep learning. A deep convolutional neural network is designed to classify holographic images of unlabeled living cells. After training, the network outperforms previous techniques in all accuracy measures, achieving single-spore sensitivity and subgenus specificity. The unique "representation learning" capability of deep learning enables direct training from raw images instead of manually extracted features. The method automatically recognizes key biological traits encoded in the images and exploits them as fingerprints. This remarkable learning ability makes the proposed method readily applicable to classifying various single cells in addition to B. anthracis, as demonstrated for the diagnosis of Listeria monocytogenes, without any modification. We believe that our strategy will make holographic microscopy more accessible to medical doctors and biomedical scientists for easy, rapid, and accurate point-of-care diagnosis of pathogens.

Holographic deep learning for rapid optical screening of anthrax spores

Establishing early warning systems for anthrax attacks is crucial in biodefense. Despite numerous studies for decades, the limited sensitivity of conventional biochemical methods essentially requires preprocessing steps and thus has limitations to be used in realistic settings of biological warfare. We present an optical method for rapid and label-free screening of Bacillus anthracis spores through the synergistic application of holographic microscopy and deep learning. A deep convolutional neural network is designed to classify holographic images of unlabeled living cells. After training, the network outperforms previous techniques in all accuracy measures, achieving single-spore sensitivity and subgenus specificity. The unique "representation learning" capability of deep learning enables direct training from raw images instead of manually extracted features. The method automatically recognizes key biological traits encoded in the images and exploits them as fingerprints. This remarkable learning ability makes the proposed method readily applicable to classifying various single cells in addition to B. anthracis, as demonstrated for the diagnosis of Listeria monocytogenes, without any modification. We believe that our strategy will make holographic microscopy more accessible to medical doctors and biomedical scientists for easy, rapid, and accurate point-of-care diagnosis of pathogens.

Comparative analysis of the sensitivity of metagenomic sequencing and PCR to detect a biowarfare simulant (Bacillus atrophaeus) in soil samples

To evaluate the sensitivity of high-throughput DNA sequencing for monitoring biowarfare agents in the environment, we analysed soil samples inoculated with different amounts of Bacillus atrophaeus, a surrogate organism for Bacillus anthracis. The soil samples considered were a poorly carbonated soil of the silty sand class, and a highly carbonated soil of the silt class. Control soil samples and soil samples inoculated with 10, 10³, or 10⁵ cfu were processed for DNA extraction. About 1% of the DNA extracts was analysed through the sequencing of more than 10⁸ reads. Similar amounts of extracts were also studied for Bacillus atrophaeus DNA content by real-time PCR. We demonstrate that, for both soils, high-throughput sequencing is at least equally sensitive than real-time PCR to detect Bacillus atrophaeus DNA. We conclude that metagenomics allows the detection of less than 10 ppm of DNA from a biowarfare simulant in complex environmental samples.

Construction of Bacillus thuringiensis Simulant Strains Suitable for Environmental Release

For a surrogate bacterium to be used in outdoor studies, it is important to consider environmental and human safety and ease of detection. Recently, Bacillus thuringiensis, a popular bioinsecticide bacterium, has been gaining attention as a surrogate bacterium for use in biodefense. In this study, we constructed simulant strains of B. thuringiensis with enhanced characteristics for environmental studies. Through transposon mutagenesis, pigment genes were inserted into the chromosome, producing yellow-colored colonies for easy detection. To prevent persistence of spores in the environment, a genetic circuit was designed to produce a spore without sporulation capability. Two loxP sites were inserted, one on each side of the spo0A gene, which encodes a sporulation master regulator, and a sporulation-dependent Cre expression cassette was inserted into the chromosome. This genetic circuit successfully deleted spo0A during sporulation, producing spores that lacked the spo0A gene. In addition, two major α/β-type small acid-soluble spore protein (SASP) genes, predicted by synteny analysis, were deleted. The spores of the mutant strain showed increased UV-C sensitivity and quickly lost viability when tested in a solar simulator. When the spores of the mutant strain were administered to the lungs of BALB/c mice, cells were quickly removed from the body, suggesting enhanced in vivo safety. All strains constructed in this study contain no antibiotic resistance markers and all heterologous genes were inserted into the chromosome, which are useful features for simulants to be released into the environment.IMPORTANCEB. thuringiensis has recently been receiving increasing attention as a good spore simulant in biodefense research. However, few studies were done to properly address many important features of B. thuringiensis as a simulant in environmental studies. Since spores can persist in the environment for years after release, environmental contamination is a big problem, especially when genetically engineered strains are used. To solve these problems, we report here the development of B. thuringiensis simulant strains that are capable of forming yellow colonies for easy detection, incapable of forming spores more than once due to a genetic circuit, and lacking in two major SASP genes. The genetic circuit to produce a spore without sporulation capability, together with the deletion of SASP genes, ensures the environmental and human safety of the simulant strains developed in this study. All of these features will allow wider use of B. thuringiensis as a simulant for Bacillus anthracis in environmental release studies.

Considerations for estimating microbial environmental data concentrations collected from a field setting

In the event of an indoor release of an environmentally persistent microbial pathogen such as Bacillus anthracis, the potential for human exposure will be considered when remedial decisions are made. Microbial site characterization and clearance sampling data collected in the field might be used to estimate exposure. However, there are many challenges associated with estimating environmental concentrations of B. anthracis or other spore-forming organisms after such an event before being able to estimate exposure. These challenges include: (1) collecting environmental field samples that are adequate for the intended purpose, (2) conducting laboratory analyses and selecting the reporting format needed for the laboratory data, and (3) analyzing and interpreting the data using appropriate statistical techniques. This paper summarizes some key challenges faced in collecting, analyzing, and interpreting microbial field data from a contaminated site. Although the paper was written with considerations for B. anthracis contamination, it may also be applicable to other bacterial agents. It explores the implications and limitations of using field data for determining environmental concentrations both before and after decontamination. Several findings were of interest. First, to date, the only validated surface/sampling device combinations are swabs and sponge-sticks on stainless steel surfaces, thus limiting availability of quantitative analytical results which could be used for statistical analysis. Second, agreement needs to be reached with the analytical laboratory on the definition of the countable range and on reporting of data below the limit of quantitation. Finally, the distribution of the microbial field data and statistical methods needed for a particular data set could vary depending on these data that were collected, and guidance is needed on appropriate statistical software for handling microbial data. Further, research is needed to develop better methods to estimate human exposure from pathogens using environmental data collected from a field setting.

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.

Inactivation of Bacillus anthracis Spores during Laboratory-Scale Composting of Feedlot Cattle Manure

Anthrax outbreaks in livestock have social, economic and health implications, altering farmer’s livelihoods, impacting trade and posing a zoonotic risk. Our study investigated the survival of Bacillus thuringiensis and B. anthracis spores sporulated at 15, 20, or 37°C, over 33 days of composting. Spores (∼7.5 log₁₀ CFU g^-1) were mixed with manure and composted in laboratory scale composters. After 15 days, the compost was mixed and returned to the composter for a second cycle. Temperatures peaked at 71°C on day 2 and remained ≥55°C for an average of 7 days in the first cycle, but did not exceed 55°C in the second. For B. thuringiensis, spores generated at 15 and 21°C exhibited reduced (P < 0.05) viability of 2.7 and 2.6 log₁₀ CFU g^-1 respectively, as compared to a 0.6 log₁₀ CFU g^-1 reduction for those generated at 37°C. For B. anthracis, sporulation temperature did not impact spore survival as there was a 2.5, 2.2, and 2.8 log₁₀ CFU g^-1 reduction after composting for spores generated at 15, 21, and 37°C, respectively. For both species, spore viability declined more rapidly (P < 0.05) in the first as compared to the second composting cycle. Our findings suggest that the duration of thermophilic exposure (≥55°C) is the main factor influencing survival of B. anthracis spores in compost. As sporulation temperature did not influence survival of B. anthracis, composting may lower the viability of spores associated with carcasses infected with B. anthracis over a range of sporulation temperatures.

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

AIM

To develop test methods and evaluate survival of Bacillus thuringiensis kurstaki cry(-) HD-1 and B. thuringiensis Al Hakam spores after exposure to hot, humid air inside of a C-130 aircraft.

METHODS AND RESULTS

Bacillus thuringiensis spores were either pre-inoculated on 1 × 2 or 2 × 2 cm substrates or aerosolized inside the cargo hold of a C-130 and allowed to dry. Dirty, complex surfaces (10 × 10 cm) swabbed after spore dispersal showed a deposition of 8-10 log10 m(-2) through the entire cargo hold. After hot, humid air decontamination at 75-80°C, 70-90% relative humidity for 7 days, 87 of 98 test swabs covering 0·98 m(2) , showed complete spore inactivation. There was a total of 1·67 log10 live CFU detected in 11 of the test swabs. Spore inactivation in the 98 test swabs was measured at 7·06 log10 m(-2) .

CONCLUSIONS

Laboratory test methods for hot, humid air decontamination were scaled for a large-scale aircraft field test. The C-130 field test demonstrated that hot, humid air can be successfully used to decontaminate an aircraft.

SIGNIFICANCE AND IMPACT OF THE STUDY

Transition of a new technology from research and development to acquisition at a Technology Readiness Level 7 is unprecedented.

Whole-Genome Sequencing in Microbial Forensic Analysis of Gamma-Irradiated Microbial Materials

Effective microbial forensic analysis of materials used in a potential biological attack requires robust methods of morphological and genetic characterization of the attack materials in order to enable the attribution of the materials to potential sources and to exclude other potential sources. The genetic homogeneity and potential intersample variability of many of the category A to C bioterrorism agents offer a particular challenge to the generation of attributive signatures, potentially requiring whole-genome or proteomic approaches to be utilized. Currently, irradiation of mail is standard practice at several government facilities judged to be at particularly high risk. Thus, initial forensic signatures would need to be recovered from inactivated (nonviable) material. In the study described in this report, we determined the effects of high-dose gamma irradiation on forensic markers of bacterial biothreat agent surrogate organisms with a particular emphasis on the suitability of genomic DNA (gDNA) recovered from such sources as a template for whole-genome analysis. While irradiation of spores and vegetative cells affected the retention of Gram and spore stains and sheared gDNA into small fragments, we found that irradiated material could be utilized to generate accurate whole-genome sequence data on the Illumina and Roche 454 sequencing platforms.

Heat and desiccation are the predominant factors affecting inactivation of Bacillus licheniformis and Bacillus thuringiensis spores during simulated composting

AIMS

The suitability of composting for disposal of livestock mortalities due to Bacillus anthracis was assessed by measuring viability of surrogate spores from two strains each of Bacillus licheniformis and Bacillus thuringiensis after a heating cycle modelled on a cattle composting study.

METHODS AND RESULTS

Sporulation was attempted from 10 to 37°C, but poor yields at lower temperatures resulted in 25, 30 and 37°C being selected to generate sufficient spores (8 log10  CFU ml(-1) ) for experiments. Spores were inoculated into 3 g autoclaved dried-ground compost rehydrated with 6 ml water or silica beads in a factorial design for each strain, sporulation temperature, matrix and sampling day (0, 25, 50, 100, 150). Maximum incubation temperature was 62°C, but spores were maintained at ≥55°C for 78 of 150 days. Although significant differences existed among Bacillus strains and sporulation temperatures, numbers of viable spores after 150 days averaged 1·3 log10  CFU g(-1) , a 5·2 log10 reduction from day 0.

CONCLUSIONS

Spore inactivation was likely due to heat and desiccation as matrices were autoclaved prior to incubation, negating impacts of microflora.

SIGNIFICANCE AND IMPACT OF STUDY

Results support composting for disposal of anthrax mortalities, provided long-term thermophillic heating is achieved. Due to limited sporulation at 10°C, livestock mortalities from anthrax at this or lower ambient temperatures would likely be of lower risk for disease transmission.

Decontamination Efficacy and Skin Toxicity of Two Decontaminants against Bacillus anthracis

Decontamination of bacterial endospores such as Bacillus anthracis has traditionally required the use of harsh or caustic chemicals. The aim of this study was to evaluate the efficacy of a chlorine dioxide decontaminant in killing Bacillus anthracis spores in solution and on a human skin simulant (porcine cadaver skin), compared to that of commonly used sodium hypochlorite or soapy water decontamination procedures. In addition, the relative toxicities of these decontaminants were compared in human skin keratinocyte primary cultures. The chlorine dioxide decontaminant was similarly effective to sodium hypochlorite in reducing spore numbers of Bacillus anthracis Ames in liquid suspension after a 10 minute exposure. After five minutes, the chlorine dioxide product was significantly more efficacious. Decontamination of isolated swine skin contaminated with Bacillus anthracis Sterne with the chlorine dioxide product resulted in no viable spores sampled. The toxicity of the chlorine dioxide decontaminant was up to two orders of magnitude less than that of sodium hypochlorite in human skin keratinocyte cultures. In summary, the chlorine dioxide based decontaminant efficiently killed Bacillus anthracis spores in liquid suspension, as well as on isolated swine skin, and was less toxic than sodium hypochlorite in cultures of human skin keratinocytes.

Test methods and response surface models for hot, humid air decontamination of materials contaminated with dirty spores of Bacillus anthracis ∆Sterne and Bacillus thuringiensis Al Hakam

AIMS

To develop test methods and evaluate survival of Bacillus anthracis ∆Sterne or Bacillus thuringiensis Al Hakam on materials contaminated with dirty spore preparations after exposure to hot, humid air using response surface modelling.

METHODS AND RESULTS

Spores (>7 log10 ) were mixed with humic acid + spent sporulation medium (organic debris) or kaolin (dirt debris). Spore samples were then dried on five different test materials (wiring insulation, aircraft performance coating, anti-skid, polypropylene, and nylon). Inoculated materials were tested with 19 test combinations of temperature (55, 65, 75°C), relative humidity (70, 80, 90%) and time (1, 2, 3 days). The slowest spore inactivation kinetics was on nylon webbing and/or after addition of organic debris.

CONCLUSIONS

Hot, humid air effectively decontaminates materials contaminated with dirty Bacillus spore preparations; debris and material interactions create complex decontamination kinetic patterns; and B. thuringiensis Al Hakam is a realistic surrogate for B. anthracis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Response surface models of hot, humid air decontamination were developed which may be used to select decontamination parameters for contamination scenarios including aircraft.

Use of Enterococcus faecalis and Bacillus atrophaeus as surrogates to establish and maintain laboratory proficiency for concentration of water samples using ultrafiltration

The U.S. Environmental Protection Agency's (EPA) Water Laboratory Alliance (WLA) currently uses ultrafiltration (UF) for concentration of biosafety level 3 (BSL-3) agents from large volumes (up to 100-L) of drinking water prior to analysis. Most UF procedures require comprehensive training and practice to achieve and maintain proficiency. As a result, there was a critical need to develop quality control (QC) criteria. Because select agents are difficult to work with and pose a significant safety hazard, QC criteria were developed using surrogates, including Enterococcus faecalis and Bacillus atrophaeus. This article presents the results from the QC criteria development study and results from a subsequent demonstration exercise in which E. faecalis was used to evaluate proficiency using UF to concentrate large volume drinking water samples. Based on preliminary testing EPA Method 1600 and Standard Methods 9218, for E. faecalis and B. atrophaeus respectively, were selected for use during the QC criteria development study. The QC criteria established for Method 1600 were used to assess laboratory performance during the demonstration exercise. Based on the results of the QC criteria study E. faecalis and B. atrophaeus can be used effectively to demonstrate and maintain proficiency using ultrafiltration.

The impact of inducing germination of Bacillus anthracis and Bacillus thuringiensis spores on potential secondary decontamination strategies

AIMS

Decontamination and remediation of a site contaminated by the accidental or intentional release of fully virulent Bacillus anthracis spores are difficult, costly and potentially damaging to the environment. Development of novel decontamination strategies that have minimal environmental impacts remains a high priority. Although ungerminated spores are amongst the most resilient organisms known, once exposed to germinants, the germinating spores, in some cases, become susceptible to antimicrobial environments. We evaluated the concept that once germinated, B. anthracis spores would be less hazardous and significantly easier to remediate than ungerminated dormant spores.

METHODS AND RESULTS

Through in vitro germination and sensitivity assays, we demonstrated that upon germination, B. anthracis Ames spores and Bacillus thuringiensis Al Hakam spores (serving as a surrogate for B. anthracis) become susceptible to environmental stressors. The majority of these germinated B. anthracis and B. thuringiensis spores were nonviable after exposure to a defined minimal germination-inducing solution for prolonged periods of time. Additionally, we examined the impact of potential secondary disinfectant strategies including bleach, hydrogen peroxide, formaldehyde and artificial UV-A, UV-B and UV-C radiation, employed after a 60-min germination-induction step. Each secondary disinfectant employs a unique mechanism of killing; as a result, germination-induction strategies are better suited for some secondary disinfectants than others.

CONCLUSIONS

These results provide evidence that the deployment of an optimal combination strategy of germination-induction/secondary disinfection may be a promising aspect of wide-area decontamination following a B. anthracis contamination event.

SIGNIFICANCE AND IMPACT OF THE STUDY

By inducing spores to germinate, our data confirm that the resulting cells exhibit sensitivities that can be leveraged when paired with certain decontamination measures. This increased susceptibility could be exploited to devise more efficient and safe decontamination measures and may obviate the need for more stringent methods that are currently in place.