Young W. Choi

A Preliminary Assessment of Silver Nanoparticle Inhibition of Monkeypox Virus Plaque Formation

The use of nanotechnology and nanomaterials in medical research is growing. Silver-containing nanoparticles have previously demonstrated antimicrobial efficacy against bacteria and viral particles. This preliminary study utilized an in vitro approach to evaluate the ability of silver-based nanoparticles to inhibit infectivity of the biological select agent, monkeypox virus (MPV). Nanoparticles (10–80 nm, with or without polysaccharide coating), or silver nitrate (AgNO3) at concentrations of 100, 50, 25, and 12.5 μg/mL were evaluated for efficacy using a plaque reduction assay. Both Ag-PS-25 (polysaccharide-coated, 25 nm) and Ag-NP-55 (non-coated, 55 nm) exhibited a significant (P ≤ 0.05) dose-dependent effect of test compound concentration on the mean number of plaque-forming units (PFU). All concentrations of silver nitrate (except 100 μg/mL) and Ag-PS-10 promoted significant (P ≤ 0.05) decreases in the number of observed PFU compared to untreated controls. Some nanoparticle treatments led to increased MPV PFU ranging from 1.04- to 1.8-fold above controls. No cytotoxicity (Vero cell monolayer sloughing) was caused by any test compound, except 100 μg/mL AgNO3. These results demonstrate that silver-based nanoparticles of approximately 10 nm inhibit MPV infection in vitro, supporting their potential use as an anti-viral therapeutic.

Decontamination assessment of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surfaces using a hydrogen peroxide gas generator

Aims:  To evaluate the decontamination of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surface materials using hydrogen peroxide gas.

Formaldehyde gas inactivation of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surface materials

Aims: To evaluate the decontamination of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surface materials using formaldehyde gas.

Environmental Persistence of a Highly Pathogenic Avian Influenza (H5N1) Virus

Human cases of disease caused by highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype are rare, yet characterized with a mortality rate of approximately 60%. Tests were conducted to determine the environmental persistence of an HPAI (H5N1) virus on four materials (glass, wood, galvanized metal, and topsoil) that could act as fomites or harbor the virus. Test coupons were inoculated with the virus and exposed to one of five environmental conditions that included changes in temperature, relative humidity, and simulated sunlight. At time periods up to 13 days, the virus was extracted from each coupon, and quantified via cytopathic effects on Madin-Darby canine kidney cells. The virus was most persistent under the low temperature condition, with less than 1 log reduction on glass and steel after 13 days at low relative humidity. Thus, at these conditions, the virus would be expected to persist appreciably beyond 13 days.

Efficacy of liquid spray decontaminants for inactivation of Bacillus anthracis spores on building and outdoor materials

Aims:  To obtain data on the efficacy of various liquid and foam decontamination technologies to inactivate Bacillus anthracis Ames and Bacillus subtilis spores on building and outdoor materials.

Vapour‐phase hydrogen peroxide inactivates Yersinia pestis dried on polymers, steel, and glass surfaces

Aims:  This study evaluated the inactivation of virulent Yersinia pestis dried on polymers, steel, and glass surfaces using vapour‐phase hydrogen peroxide.

Bacillus Anthracis Spore Inactivation by Fumigant Decontamination

In 2001, envelopes containing virulent Bacillus anthracis spores were placed into the U.S. mail, resulting in contamination of mail processing and distribution facilities and office buildings. These spore-contaminated facilities were subsequently decontaminated primarily by fumigation with hydrogen peroxide, chlorine dioxide, and formaldehyde. These highly-publicized incidents resulted in increased public awareness of the threat to human health posed by Bacillus anthracis, and increased interest in sampling, detection, and decontamination of indoor surfaces, rooms, and buildings. Fumigants offer advantages over liquid application for decontaminating rooms or buildings due to the increased coverage of large surface areas and ease of cleanup. From 2001 to the present, however, no decontamination technology has been registered by the U.S. Environmental Protection Agency (EPA) for use against B. anthracis spores; rather, decontamination has been performed through the EPAs issuance of Crisis Exemptions. Since 2001, research and testing efforts have assessed the efficacy and maturity of sporicidal fumigants as well as the maturity, chemical toxicity, material compatibility, and ventilation requirements of these technologies. Several studies have been published in the scientific literature regarding fumigant inactivation of Bacillus spores; however, most decontamination studies with fumigants have utilized surrogates for B. anthracis surrogates, which can be more resistant to a specific type of fumigant (e.g., Geobacillus stearothermophilus and vaporous hydrogen peroxide) than virulent B. anthracis. Therefore, the purpose of this review is to summarize current knowledge available in the open scientific literature describing the inactivation of virulent B. anthracis spores by various fumigating agents with respect to key operational variables that can affect fumigant decontamination efficacy, such as fumigant concentration, contact time, operational temperature, and relative humidity.

Environmental Persistence of Bacillus anthracis and Bacillus subtilis Spores

There is a lack of data for how the viability of biological agents may degrade over time in different environments. In this study, experiments were conducted to determine the persistence of Bacillus anthracis and Bacillus subtilis spores on outdoor materials with and without exposure to simulated sunlight, using ultraviolet (UV)-A/B radiation. Spores were inoculated onto glass, wood, concrete, and topsoil and recovered after periods of 2, 14, 28, and 56 days. Recovery and inactivation kinetics for the two species were assessed for each surface material and UV exposure condition. Results suggest that with exposure to UV, decay of spore viability for both Bacillus species occurs in two phases, with an initial rapid decay, followed by a slower inactivation period. The exception was with topsoil, in which there was minimal loss of spore viability in soil over 56 days, with or without UV exposure. The greatest loss in viable spore recovery occurred on glass with UV exposure, with nearly a four log10 reduction after just two days. In most cases, B. subtilis had a slower rate of decay than B. anthracis, although less B. subtilis was recovered initially.

Inactivation of Francisella tularensis Schu S4 in a Biological Safety Cabinet Using Hydrogen Peroxide Fumigation

This study evaluated the inactivation of Francisella tularensis Schu S4 on various materials (acrylic, glass, polyamide, polyethylene, polypropylene, silicone rubber, and stainless steel) using hydrogen peroxide fumigation of a Class III Biological Safety Cabinet (BSC III). A suspension of F. tularensis Schu S4 (7 × 107 CFU) was dried on seven different types of test surfaces and exposed to vaporous hydrogen peroxide (VHP) fumigation for a contact time of two hours. Qualitative growth assessment showed that VHP exposure inactivated F. tularensis on all replicates of the seven test materials up to four days post-exposure. The effectiveness of VHP fumigation on the growth of biological indicators (Bacillus subtilis or Geobacillus stearothermophilus) and spore strips (Bacillus atrophaeus) was evaluated in parallel as a qualitative assessment of decontamination. At one and four days post-exposure, decontaminated biological indicators and spore strips exhibited no growth, while the non-decontaminated samples displayed growth. This study provides information for using VHP fumigation as an alternative approach for the decontamination of virulent F. tularensis when the current accepted method of 10% household bleach followed by 70% alcohol may not be practical for decontamination of a BSC III.

Environmental persistence of vaccinia virus on materials.

Smallpox is caused by the variola virus, and ranks as one of the most serious diseases that could originate from a biological weapon. However, limited data exist on the persistence of variola and related viruses on materials (that may act as fomites), under controlled environmental conditions. To fill these data gaps, we determined the persistence of the vaccinia virus (an established surrogate for the variola virus) as a function of temperature, relative humidity and material. Experiments were conducted with vaccinia virus in a freeze‐dried form, using four materials under four sets of environmental conditions. After elapsed times ranging from 1 to 56 days, the virus was extracted from small coupons and quantified via plaque‐forming units (PFU). The vaccinia virus was most persistent at low temperature and low relative humidity, with greater than 104 PFU recovered from glass, galvanized steel and painted cinder block at 56 days (equivalent to only a c. 2 log reduction). Thus, vaccinia virus may persist from weeks to months, depending on the material and environmental conditions. This study may aid those responsible for infection control to make informed decisions regarding the need for environmental decontamination following the release of an agent such as variola.