Mechanisms of killing of Bacillus subtilis spores by hypochlorite and chlorine dioxide

Electrochemical oxidation for stormwater disinfection: How does real stormwater chemistry impact on pathogen removal and disinfection by-products level?

Preliminary laboratory work has shown that electrochemical oxidation (ECO) is a promising technology for disinfection of harvested stormwater. This paper focuses on understanding how stormwater chemistry (e.g. pH, chloride, bicarbonate, ammonia and total organic carbon - that can vary substantially between sites) impacts the disinfection performance of ECO. Real stormwater samples from four different urban catchments were collected and tested for ECO performance in disinfecting stormwater pathogens using a boron doped diamond anode under the current density of 4.2 mA/cm². Results showed that total disinfection of indigenous Escherichia coli (E. coli), as well as three different stormwater pathogens (Enterococci, Campylobacter and C. perfringens) was achievable for all four tested stormwater within 30 min. Compared to the synthetic stormwater, lower disinfection rates were observed in real stormwater which has more complex chemistry. Stormwater chloride concentration was the only tested parameter that had significant impact on the treatment performance, with higher initial stormwater chloride concentration leading to an increased disinfection rate. Disinfection by-products in the treated stormwater were well below the Australian Drinking Water Guideline value for health, with its production level positively correlated to the pH values of stormwater.

Efficiency of Different Disinfectants on Bacillus cereus Sensu Stricto Biofilms on Stainless-Steel Surfaces in Contact With Milk

The species of the Bacillus cereus group have the ability to adhere to and form biofilms on solid surfaces, including stainless steel, a material widely used in food industries. Biofilms allow for recontamination during food processing, and the "clean-in-place" (CIP) system is largely used by industries to control them. This study thus proposes to evaluate the efficacy of peracetic acid and sodium hypochlorite against biofilms induced on stainless-steel surfaces. The SAMN07414939 isolate (BioProject PRJNA390851), a recognized biofilm producer, was selected for biofilm induction on AISI 304 stainless steel. Biofilm induction was performed and classified into three categories: TCP (Tindalized, Contaminated, and Pasteurized milk), TCS (Tindalized milk Contaminated with Spores), and TCV (Tindalized milk Contaminated with Vegetative cells). Subsequently, the coupons were sanitized simulating a CIP procedure, on a pilot scale, using alkaline and acid solutions followed by disinfectants (peracetic acid and sodium hypochlorite). Microorganism adhesion on the surfaces reached 6.3 × 105 to 3.1 × 107 CFU/cm-2. Results did not show significant differences (p > 0.05) for surface adhesion between the three tested categories (TCP, TCS, and TCV) or (p > 0.05) between the two disinfectants (peracetic acid and sodium hypochlorite). Microbial populations adhered to the stainless-steel coupons are equally reduced after treatment with peracetic acid and sodium hypochlorite, with no differences in the control of B. cereus s.s. biofilms on AISI 304 stainless-steel surfaces.

Synergistic effect of combined UV-LED and chlorine treatment on Bacillus subtilis spore inactivation

An ultraviolet (UV)-based advanced oxidation process (AOP) for disinfecting water is introduced in this paper. This study aimed to evaluate the potential of UV light-emitting diodes (UV-LEDs)/chlorine AOP (UV/Cl₂) for Bacillus subtilis spore inactivation. Chlorine was combined with 265 and 280 nm LEDs (UV₂₆₅/Cl₂, UV₂₈₀/Cl₂) and investigated. The addition of 4.0 mg/L of free chlorine at pH 7.0 in the presence of 125 mJ/cm² of UV irradiation resulted in an additional 1.8-log reduction in UV₂₆₅/Cl₂ and 1.5-log reduction in UV₂₈₀/Cl₂. There was no observed enhancement in spore inactivation with the addition of a radical scavenger, t-BuOH, which indicated the role of ^•OH in the synergistic effect. To quantitatively evaluate the synergism, the primary treatment with UV/Cl₂ was followed by further UV or Cl₂ treatment. After UV/Cl₂ pretreatment at different pH levels, the 265 and 280 nm LEDs treatment enhanced an approximate 0.4-0.5-log reduction compared to UV only, and Cl₂ treatment enhanced an approximate 0.7-1.1-log reduction compared to Cl₂ only. In addition, at pH 7.0, in UV₂₆₅/Cl₂-Cl₂ and UV₂₈₀/Cl₂-Cl₂, the inactivation rate constant k increased by approximately 2 and 1.5 times, respectively. The CT for the lag phases (CT_lag) reduced to approximately 67 and 58%, respectively. Similar results were obtained at pH 7.5 and 8.0, and in the secondary effluent. The synergistic effect on spore inactivation suggested that the pathogen inactivation efficiency of sequential UV and chlorine disinfection processes, which are commonly applied, can be significantly enhanced by adding chlorine prior to UV treatment.

Degradation of sulfonamide antibiotics and their intermediates toxicity in an aeration-assisted non-thermal plasma while treating strong wastewater

Aeration-assisted non-thermal plasma (NTP) process is known as promising due to simultaneous generation of oxygen- and nitrogen-based reactive chemicals for non-biodegradable pollutants removal in a wastewater. Despite its effective oxidizing capability, the decomposition mechanism of antibiotics is not yet clarified well. This study verifies the NTP's removal potential of non-biodegradable sulfonamide antibiotics in the treatment of strong wastewater. The instantaneous production of hydrogen peroxide (H₂O₂) was quantified to prove synergistic advanced oxidation, and degradation kinetic coefficients of N, N-Dimethyl-4-nitrosoaniline (RNO) reveals rapid oxidation rate of NTP. Also, the results of an acute-toxicity test using Daphnia magna demonstrate how the toxicity of antibiotics intermediates responds to the NTP. Results indicate that the NTP has better potential than conventional oxidation processes in terms of OH-radical generation due to the interplay of reactive species. This study provides useful information that aeration-assisted NTP application to wastewater treatment can be a viable option to enhance treatment efficiency via plasma-related reactive species and that how environmental ecotoxicity responds to the by-products of sulfonamide antibiotics.

Role of DNA Repair and Protective Components in Bacillus subtilis Spore Resistance to Inactivation by 400-nm-Wavelength Blue Light

The high intrinsic decontamination resistance of Firmicutes spores is important medically (disease) and commercially (food spoilage). Effective methods of spore eradication would be of considerable interest in the health care and medical product industries, particularly if the decontamination method effectively killed spores while remaining benign to both humans and sensitive equipment. Intense blue light at a ∼400 nm wavelength is one such treatment that has drawn significant interest. This work has determined the resistance of spores to blue light in an extensive panel of Bacillus subtilis strains, including wild-type strains and mutants that (i) lack protective components such as the spore coat and its pigment(s) or the DNA protective α/β-type small, acid-soluble spore proteins (SASP); (ii) have an elevated spore core water content; or (iii) lack enzymes involved in DNA repair, including those for homologous recombination and nonhomologous end joining (HR and NHEJ), apurinic/apyrimidinic endonucleases, nucleotide and base excision repair (NER and BER), translesion synthesis (TLS) by Y-family DNA polymerases, and spore photoproduct (SP) removal by SP lyase (SPL). The most important factors in spore blue light resistance were determined to be spore coats/pigmentation, α/β-type SASP, NER, BER, TLS, and SP repair. A major conclusion from this work is that blue light kills spores by DNA damage, and the results in this work indicate at least some of the specific DNA damage. It appears that high-intensity blue light could be a significant addition to the agents used to kill bacterial spores in applied settings.IMPORTANCE Effective methods of spore inactivation would be of considerable interest in the health care and medical products industries, particularly if the decontamination method effectively killed spores while remaining benign to both humans and sensitive equipment. Intense blue light radiation is one such treatment that has drawn significant interest. In this work, all known spore-protective features, as well as universal and spore-specific DNA repair mechanisms, were tested in a systematic fashion for their contribution to the resistance of spores to blue light radiation.

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.

Association between bacterial survival and free chlorine concentration during commercial fresh-cut produce wash operation

Determining the minimal effective free chlorine (FC) concentration for preventing pathogen survival and cross-contamination during produce washing is critical for developing science- and risk-based food safety practices. The correlation between dynamic FC concentrations and bacterial survival was investigated during commercial washing of chopped Romaine lettuce, shredded Iceberg lettuce, and diced cabbage as pathogen inoculation study during commercial operation is not feasible. Wash water was sampled every 30 min and assayed for organic loading, FC, and total aerobic mesophilic bacteria after chlorine neutralization. Water turbidity, chemical oxygen demand, and total dissolved solids increased significantly over time, with more rapid increases in diced cabbage water. Combined chlorine increased consistently while FC fluctuated in response to rates of chlorine dosing, product loading, and water replenishment. Total bacterial survival showed a strong correlation with real-time FC concentration. Under approximately 10 mg/L, increasing FC significantly reduced the frequency and population of surviving bacteria detected. Increasing FC further resulted in the reduction of the aerobic plate count to below the detection limit (50 CFU/100 mL), except for a few sporadic positive samples with low cell counts. This study confirms that maintaining at least 10 mg/L FC in wash water strongly reduced the likelihood of bacterial survival and thus potential cross contamination of washed produce.

Application of High Pressure with Homogenization, Temperature, Carbon Dioxide, and Cold Plasma for the Inactivation of Bacterial Spores: A Review

Formation of highly resistant spores is a concern for the safety of low-acid foods as they are a perfect vehicle for food spoilage and/or human infection. For spore inactivation, the strategy usually applied in the food industry is the intensification of traditional preservation methods to sterilization levels, which is often accompanied by decreases of nutritional and sensory properties. In order to overcome these unwanted side effects in food products, novel and emerging sterilization technologies are being developed, such as pressure-assisted thermal sterilization, high-pressure carbon dioxide, high-pressure homogenization, and cold plasma. In this review, the application of these emergent technologies is discussed, in order to understand the effects on bacterial spores and their inactivation and thus ensure food safety of low-acid foods. In general, the application of these novel technologies for inactivating spores is showing promising results. However, it is important to note that each technique has specific features that can be more suitable for a particular type of product. Thus, the most appropriate sterilization method for each product (and target microorganisms) should be assessed and carefully selected.

Effect of Sterilants on Amplification and Detection of Target DNA from Bacillus cereus Spores

To conceal criminal activity of a bioterrorist or agroterrorist, the site of pathogen generation is often treated with sterilants to kill the organisms and remove evidence. As dead organisms cannot be analyzed by culture, this study examined whether DNA from sterilant-treated Bacillus cereus spores was viable for amplification. The spores were exposed to five common sterilants: bleach, Sterilox®, oxidizer foam (L-Gel), a peroxyacid (Actril®), and formaldehyde vapor. The spores were inoculated on typical surfaces found in offices and laboratories to test for environmental effects. It was found that the surface influenced the efficiency of recovery of the organisms. The DNA isolated from the recovered spores was successfully detected using RT-qPCR for all treatments except for formaldehyde, by amplifying the phosphatidylinositol phospholipase C and sphingomyelinase genes. The results demonstrated that evidence from sites treated with sterilants can still provide information on the uncultured organism, using DNA amplification.

Microbicidal effects of weakly acidified chlorous acid water against feline calicivirus and Clostridium difficile spores under protein-rich conditions

Sanitation of environmental surfaces with chlorine based-disinfectants is a principal measure to control outbreaks of norovirus or Clostridium difficile. The microbicidal activity of chlorine-based disinfectants depends on the free available chlorine (FAC), but their oxidative potential is rapidly eliminated by organic matter. In this study, the microbicidal activities of weakly acidified chlorous acid water (WACAW) and sodium hypochlorite solution (NaClO) against feline calcivirus (FCV) and C. difficile spores were compared in protein-rich conditions. WACAW inactivated FCV and C. difficile spores better than NaClO under all experimental conditions used in this study. WACAW above 100 ppm FAC decreased FCV >4 log10 within 30 sec in the presence of 0.5% each of bovine serum albumin (BSA), polypeptone or meat extract. Even in the presence of 5% BSA, WACAW at 600 ppm FAC reduced FCV >4 log10 within 30 sec. Polypeptone inhibited the virucidal activity of WACAW against FCV more so than BSA or meat extract. WACAW at 200 ppm FAC decreased C. difficile spores >3 log10 within 1 min in the presence of 0.5% polypeptone. The microbicidal activity of NaClO was extensively diminished in the presence of organic matter. WACAW recovered its FAC to the initial level after partial neutralization by sodium thiosulfate, while no restoration of the FAC was observed in NaClO. These results indicate that WACAW is relatively stable under organic matter-rich conditions and therefore may be useful for treating environmental surfaces contaminated by human excretions.

Decontamination of Bacillus spores adhered to iron and cement-mortar drinking water infrastructure in a model system using disinfectants

Decontamination of Bacillus spores adhered to common drinking water infrastructure surfaces was evaluated using a variety of disinfectants. Corroded iron and cement-mortar lined iron represented the infrastructure surfaces, and were conditioned in a 23 m long, 15 cm diameter (75 ft long, 6 in diameter) pilot-scale drinking water distribution pipe system. Decontamination was evaluated using increased water velocity (flushing) alone at 0.5 m s^-1 (1.7 ft s^-1), as well as free chlorine (5 and 25 mg L^-1), monochloramine (25 mg L^-1), chlorine dioxide (5 and 25 mg L^-1), ozone (2.0 mg L^-1), peracetic acid 25 mg L^-1) and acidified nitrite (0.1 mol L^-1 at pH 2 and 3), all followed by flushing at 0.3 m s^-1 (1 ft s^-1). Flushing alone reduced the adhered spores by 0.5 and 2.0 log₁₀ from iron and cement-mortar, respectively. Log₁₀ reduction on corroded iron pipe wall coupons ranged from 1.0 to 2.9 at respective chlorine dioxide concentrations of 5 and 25 mg L^-1, although spores were undetectable on the iron surface during disinfection at 25 mg L^-1. Acidified nitrite (pH 2, 0.1 mol L^-1) yielded no detectable spores on the iron surface during the flushing phase after disinfection. Chlorine dioxide was the best performing disinfectant with >3.0 log₁₀ removal from cement-mortar at 5 and 25 mg L^-1. The data show that free chlorine, monochloramine, ozone and chlorine dioxide followed by flushing can reduce adhered spores by > 3.0 log₁₀ on cement-mortar.

Correlation of Conformational Changes and Protein Degradation with Loss of Lysozyme Activity Due to Chlorine Dioxide Treatment

Chlorine dioxide (ClO₂) is a potent oxidizing agent used for the treatment of drinking water and decontamination of facilities and equipment. The purpose of this research is to elucidate the manner in which ClO₂ destroys proteins by studying the effects of ClO₂ on lysozyme. The degree of enzyme activity lost can be correlated to the treatment time and levels of the ClO₂ used. Lysozyme activity was drastically reduced to 45.3% of original enzyme activity when exposed to 4.3 mM ClO₂ in the sample after 3 h. Almost all activities were lost in 3 h after exposure to higher ClO₂ concentrations of up to 16.8 and 21.9 mM. Changes in protein conformation and amount as a result of ClO₂ treatment were determined using the Raman spectroscopy and gel electrophoresis. Raman shifts and the alteration of spectral features observed in the ClO₂-treated lysozyme samples are associated with loss of the α-helix secondary structure, tertiary structure, and disulfide bond. Progressive degradation of the denatured lysozyme by increasing levels of chlorine dioxide was also observed in gel electrophoresis. Hence, ClO₂ can effectively cause protein denaturation and degradation resulting in loss of enzyme activity.

A pilot study on using chlorine dioxide gas for disinfection of gastrointestinal endoscopes

OBJECTIVES

This pilot study of employing chlorine dioxide (CD) gas to disinfect gastrointestinal endoscopes was conducted to meet the expectations of many endoscopy units in China for a high-efficiency and low-cost disinfectant.

METHODS

An experimental prototype with an active circulation mode was designed to use CD gas to disinfect gastrointestinal endoscopes. One type of testing device composed of polytetrafluoroethylene (PTFE) tubes (2 m long, inner diameter 1 mm) and bacterial carrier containers was used to simulate the channel of the endoscope. PTFE bacterial carriers inoculated with Bacillus atrophaeus with or without organic burden were used to evaluate the sporicidal activity of CD gas. Factors including exposure dosage, relative humidity (RH), and flow rate (FR) influencing the disinfection effect of CD gas were investigated. Moreover, an autoptic disinfecting test on eight real gastrointestinal endoscopes after clinical use was performed using the experimental prototype.

RESULTS

RH, exposure dosage, organic burden, and the FR through the channel significantly (P<0.05) affected the disinfection efficacy of CD gas for a long and narrow lumen. The log reduction increased as FR decreased. Treatment with 4 mg/L CD gas for 30 min at 0.8 L/min FR and 75% RH, resulted in complete inactivation of spores. Furthermore, all eight endoscopes with a maximum colony-forming unit of 915 were completely disinfected. The cost was only 3 CNY (0.46 USD) for each endoscope.

CONCLUSIONS

The methods and results reported in this study could provide a basis for further studies on using CD gas for the disinfection of endoscopes.

Sensing and inactivation of Bacillus anthracis Sterne by polymer-bromine complexes

We report on the performance of brominated poly(N-vinylpyrrolidone) (PVP-Br), brominated poly(ethylene glycol) (PEG-Br), and brominated poly(allylamine-co-4-aminopyridine) (PAAm-APy-Br) for their ability to decontaminate Bacillus anthracis Sterne spores in solution while also allowing for the sensing of the spores. The polymers were brominated by bromine using carbon tetrachloride or potassium tribromide as solvents, with bromine loadings ranging from 1.6 to 4.2 mEq/g of polymer. B. anthracis Sterne spores were exposed to increasing concentrations of brominated polymers for 5 min, while the kinetics of the sporicidal activity was assessed. All brominated polymers demonstrated spore log-kills of 8 within 5 min of exposure at 12 mg/mL aqueous polymer concentration. Sensing of spores was accomplished by measuring the release of dipicolinic acid (DPA) from the spore using time-resolved fluorescence. Parent, non-brominated polymers did not cause any release of DPA and the spores remained viable. In contrast, spores exposed to the brominated polymers were inactivated and the release of DPA was observed within minutes of exposure. Also, this release of DPA continued for a long time after spore inactivation as in a controlled release process. The DPA release was more pronounced for spores exposed to brominated PVP and brominated PEG-8000 compared to brominated PAAm-APy and brominated PEG-400. Using time-resolved fluorescence, we detected as low as 2500 B. anthracis spores, with PEG-8000 being more sensitive to low spore numbers. Our results suggest that the brominated polymers may be used effectively as decontamination agents against bacterial spores while also providing the sensing capability.

Bacillus subtilis Spore Inner Membrane Proteome

The endospore is the dormant form of Bacillus subtilis and many other Firmicutes. By sporulation, these spore formers can survive very harsh physical and chemical conditions. Yet, they need to go through germination to return to their growing form. The spore inner membrane (IM) has been shown to play an essential role in triggering the initiation of germination. In this study, we isolated the IM of bacterial spores, in parallel with the isolation of the membrane of vegetative cells. With the use of GeLC-MS/MS, over 900 proteins were identified from the B. subtilis spore IM preparations. By bioinformatics-based membrane protein predictions, ca. one-third could be predicted to be membrane-localized. A large number of unique proteins as well as proteins common to the two membrane proteomes were identified. In addition to previously known IM proteins, a number of IM proteins were newly identified, at least some of which are likely to provide new insights into IM physiology, unveiling proteins putatively involved in spore germination machinery and hence putative germination inhibition targets.

Mechanism of Bacillus subtilis spore inactivation by and resistance to supercritical CO2 plus peracetic acid

AIMS

Determine how supercritical CO2 (scCO2 ) plus peracetic acid (PAA) inactivates Bacillus subtilis spores, factors important in spore resistance to scCO2 -PAA, and if spores inactivated by scCO2 -PAA are truly dead.

METHODS AND RESULTS

Spores of wild-type B. subtilis and isogenic mutants lacking spore protective proteins were treated with scCO2 -PAA in liquid or dry at 35°C. Wild-type wet spores (aqueous suspension) were more susceptible than dry spores. Treated spores were examined for viability (and were truly dead), dipicolinic acid (DPA), mutations, permeability to nucleic acid stains, germination under different conditions, energy metabolism and outgrowth. ScCO2 -PAA-inactivated spores retained DPA, and survivors had no notable DNA damage. However, DPA was released from inactivated spores at a normally innocuous temperature (85°C), and colony formation from treated spores was salt sensitive. The inactivated spores germinated but did not outgrow, and these germinated spores had altered plasma membrane permeability and defective energy metabolism. Wet or dry coat-defective spores had increased scCO2 -PAA sensitivity, and dry spores but not wet spores lacking DNA protective proteins were more scCO2 -PAA sensitive.

CONCLUSIONS

These findings suggest that scCO2 -PAA inactivates spores by damaging spores' inner membrane. The spore coat provided scCO2 -PAA resistance for both wet and dry spores. DNA protective proteins provided scCO2 -PAA resistance only for dry spores.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results provide information on mechanisms of spore inactivation of and resistance to scCO2 -PAA, an agent with increasing use in sterilization applications.

Antimicrobial activity and stability of weakly acidified chlorous acid water

The antimicrobial activity of weakly acidified chlorous acid water (WACAW) against Staphylococcus aureus, non-pathogenic Escherichia coli, enterohemorrhagic E. coli (EHEC O157:H7), Candida albicans, and spore-forming Bacillus and Paenibacillus species was evaluated in vitro. The antiviral activity was also examined using feline calicivirus (FCV). Diluted WACAW (>100 ppm) effectively reduced the number of non-spore-forming bacteria (>4 log10 CFU reductions) within 5 min. Treatment with this sanitizer at 400 ppm for 30 min achieved>5 log10 CFU reductions in spore-forming Bacillus and Paenibacillus species while an equivalent concentration of sodium hypochlorite (NaClO) resulted in only a 0.98 and 2.72 log10 CFU reduction, respectively. The effect of this sanitizer against FCV was equivalent to that of NaClO. Immersion in WACAW (400 ppm) achieved >4 and 2.26 log10 CFU reductions in Campylobacter jejuni and EHEC, respectively, on artificially contaminated broiler carcass pieces. Finally, theantimicrobial activity of this sanitizer was shown to be maintained for at least 28 d when in contact with nonwoven fabric (100% cotton). This study showed that pH control of chlorous acid is expected to modify its antimicrobial activity and stability. WACAW is expected to have applications in various settings such as the food processing and healthcare industries.

Mechanism of Sporicidal Activity for the Synergistic Combination of Peracetic Acid and Hydrogen Peroxide

There is still great interest in controlling bacterial endospores. The use of chemical disinfectants and, notably, oxidizing agents to sterilize medical devices is increasing. With this in mind, hydrogen peroxide (H2O2) and peracetic acid (PAA) have been used in combination, but until now there has been no explanation for the observed increase in sporicidal activity. This study provides information on the mechanism of synergistic interaction of PAA and H2O2 against bacterial spores. We performed investigations of the efficacies of different combinations, including pretreatments with the two oxidizers, against wild-type spores and a range of spore mutants deficient in the spore coat or small acid-soluble spore proteins. The concentrations of the two biocides were also measured in the reaction vessels, enabling the assessment of any shift from H2O2 to PAA formation. This study confirmed the synergistic activity of the combination of H2O2 and PAA. However, we observed that the sporicidal activity of the combination is largely due to PAA and not H2O2. Furthermore, we observed that the synergistic combination was based on H2O2 compromising the spore coat, which was the main spore resistance factor, likely allowing better penetration of PAA and resulting in the increased sporicidal activity.

Inactivation Kinetics and Mechanism of a Human Norovirus Surrogate on Stainless Steel Coupons via Chlorine Dioxide Gas

Acute gastroenteritis caused by human norovirus is a significant public health issue. Fresh produce and seafood are examples of high-risk foods associated with norovirus outbreaks. Food contact surfaces also have the potential to harbor noroviruses if exposed to fecal contamination, aerosolized vomitus, or infected food handlers. Currently, there is no effective measure to decontaminate norovirus on food contact surfaces. Chlorine dioxide (ClO2) gas is a strong oxidizer and is used as a decontaminating agent in food processing plants. The objective of this study was to determine the kinetics and mechanism of ClO2 gas inactivation of a norovirus surrogate, murine norovirus 1 (MNV-1), on stainless steel (SS) coupons. MNV-1 was inoculated on SS coupons at the concentration of 10(7) PFU/coupon. The samples were treated with ClO2 gas at 1, 1.5, 2, 2.5, and 4 mg/liter for up to 5 min at 25°C and a relative humidity of 85%, and virus survival was determined by plaque assay. Treatment of the SS coupons with ClO2 gas at 2 mg/liter for 5 min and 2.5 mg/liter for 2 min resulted in at least a 3-log reduction in MNV-1, while no infectious virus was recovered at a concentration of 4 mg/liter even within 1 min of treatment. Furthermore, it was found that the mechanism of ClO2 gas inactivation included degradation of viral protein, disruption of viral structure, and degradation of viral genomic RNA. In conclusion, treatment with ClO2 gas can serve as an effective method to inactivate a human norovirus surrogate on SS contact surfaces.

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.

Fighting Ebola with novel spore decontamination technologies for the military

Recently, global public health organizations such as Doctors without Borders (MSF), the World Health Organization (WHO), Public Health Canada, National Institutes of Health (NIH), and the U.S. government developed and deployed Field Decontamination Kits (FDKs), a novel, lightweight, compact, reusable decontamination technology to sterilize Ebola-contaminated medical devices at remote clinical sites lacking infra-structure in crisis-stricken regions of West Africa (medical waste materials are placed in bags and burned). The basis for effectuating sterilization with FDKs is chlorine dioxide (ClO2) produced from a patented invention developed by researchers at the US Army Natick Soldier RD&E Center (NSRDEC) and commercialized as a dry mixed-chemical for bacterial spore decontamination. In fact, the NSRDEC research scientists developed an ensemble of ClO2 technologies designed for different applications in decontaminating fresh produce; food contact and handling surfaces; personal protective equipment; textiles used in clothing, uniforms, tents, and shelters; graywater recycling; airplanes; surgical instruments; and hard surfaces in latrines, laundries, and deployable medical facilities. These examples demonstrate the far-reaching impact, adaptability, and versatility of these innovative technologies. We present herein the unique attributes of NSRDEC's novel decontamination technologies and a Case Study of the development of FDKs that were deployed in West Africa by international public health organizations to sterilize Ebola-contaminated medical equipment. FDKs use bacterial spores as indicators of sterility. We review the properties and structures of spores and the mechanisms of bacterial spore inactivation by ClO2. We also review mechanisms of bacterial spore inactivation by novel, emerging, and established non-thermal technologies for food preservation, such as high pressure processing, irradiation, cold plasma, and chemical sanitizers, using an array of Bacillus subtilis mutants to probe mechanisms of spore germination and inactivation. We employ techniques of high-resolution atomic force microscopy and phase contrast microscopy to examine the effects of γ-irradiation on bacterial spores of Bacillus anthracis, Bacillus thuringiensis, and Bacillus atrophaeus spp. and of ClO2 on B. subtilis spores, and present in detail assays using spore bio-indicators to ensure sterility when decontaminating with ClO2.

Assessing the Sporicidal Activity of Oligo-p-phenylene Ethynylenes and Their Role as Bacillus Germinants

A wide range of oligo-p-phenylene ethynylenes has been shown to exhibit good biocidal activity against both Gram-negative and Gram-positive bacteria. While cell death may occur in the dark, these biocidal compounds are far more effective in the light as a result of their ability to sensitize the production of cell-damaging reactive oxygen species. In these studies, the interactions of a specific cationic oligo-p-phenylene ethynylene with spore-forming Bacillus atrophaeus and Bacillus anthracis Sterne have been investigated. Flow cytometry assays are used to rapidly monitor cell death as well as spore germination. This compound effectively killed Bacillus anthracis Sterne vegetative cells (over 4 log reduction), presumably by severe perturbations of the bacterial cell wall and cytoplasmic membrane, while also acting as an effective spore germinant in the dark. While 2 log reduction of B. anthracis Sterne spores was observed, it is hypothesized that further killing could be achieved through enhanced germination.

Sterilization of hydrogen peroxide resistant bacterial spores with stabilized chlorine dioxide

Bacillus pumilus SAFR-032 spores isolated from a clean room environment are known to exhibit enhanced resistance to peroxide, desiccation, UV radiation and chemical disinfection than other spore-forming bacteria. The survival of B. pumilus SAFR-032 spores to standard clean room sterilization practices requires development of more stringent disinfection agents. Here, we report the effects of a stabilized chlorine dioxide-based biocidal agent against spores of B. pumilus SAFR-032 and Bacillus subtilis ATCC 6051. Viability was determined via CFU measurement after exposure. Chlorine dioxide demonstrated efficacy towards sterilization of spores of B. pumilus SAFR-032 equivalent or better than exposure to hydrogen peroxide. These results indicate efficacy of chlorine dioxide delivered through a stabilized chlorine dioxide product as a means of sterilization of peroxide- and UV-resistant spores.

Disinfection of indoor air microorganisms in stack room of university library using gaseous chlorine dioxide

As with all indoor public spaces in Taiwan, the stack rooms in public libraries should meet the air quality guidelines laid down by the Taiwan Environmental Protection Administration. Accordingly, utilizing a university library in Taiwan for experimental purposes, this study investigates the efficiency of gaseous chlorine dioxide (ClO2) as a disinfection agent when applied using three different treatment modes, namely a single-daily disinfection mode (SIM), a twice-daily disinfection mode (TWM), and a triple-daily disinfection mode (TRM). For each treatment mode, the ClO2 is applied using an ultrasonic aerosol device and is performed both under natural lighting conditions and under artificial lighting conditions. The indoor air quality is evaluated before and after each treatment session by measuring the bioaerosol levels of bacteria and fungi. The results show that for all three disinfection modes, the application of ClO2 reduces the indoor bacteria and fungi concentrations to levels lower than those specified by the Taiwan EPA (i.e., bacteria <1500 CFU/m(3), fungi <1000 CFU/m(3)), irrespective of the lighting conditions under which the disinfection process is performed. For each disinfection mode, a better disinfection efficiency is obtained under natural lighting conditions since ClO2 readily decomposes under strong luminance levels. Among the three treatment modes, the disinfection efficiencies of the TWM and TRM modes are very similar under natural lighting conditions and are significantly better than that of the SIM mode. Thus, overall, the results suggest that the TWM treatment protocol represents the most cost-effective and efficient method for meeting the indoor air quality requirements of the Taiwan EPA.

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.

The Portable Chemical Sterilizer (PCS), D-FENS, and D-FEND ALL: novel chlorine dioxide decontamination technologies for the military

There is a stated Army need for a field-portable, non-steam sterilizer technology that can be used by Forward Surgical Teams, Dental Companies, Veterinary Service Support Detachments, Combat Support Hospitals, and Area Medical Laboratories to sterilize surgical instruments and to sterilize pathological specimens prior to disposal in operating rooms, emergency treatment areas, and intensive care units. The following ensemble of novel, 'clean and green' chlorine dioxide technologies are versatile and flexible to adapt to meet a number of critical military needs for decontamination(6,15). Specifically, the Portable Chemical Sterilizer (PCS) was invented to meet urgent battlefield needs and close critical capability gaps for energy-independence, lightweight portability, rapid mobility, and rugged durability in high intensity forward deployments(3). As a revolutionary technological breakthrough in surgical sterilization technology, the PCS is a Modern Field Autoclave that relies on on-site, point-of-use, at-will generation of chlorine dioxide instead of steam. Two (2) PCS units sterilize 4 surgical trays in 1 hr, which is the equivalent throughput of one large steam autoclave (nicknamed "Bertha" in deployments because of its cumbersome size, bulky dimensions, and weight). However, the PCS operates using 100% less electricity (0 vs. 9 kW) and 98% less water (10 vs. 640 oz.), significantly reduces weight by 95% (20 vs. 450 lbs, a 4-man lift) and cube by 96% (2.1 vs. 60.2 ft(3)), and virtually eliminates the difficult challenges in forward deployments of repairs and maintaining reliable operation, lifting and transporting, and electrical power required for steam autoclaves.

Life cycle and spore resistance of spore-forming Bacillus atrophaeus

Bacillus endospores have a wide variety of important medical and industrial applications. This is an overview of the fundamental aspects of the life cycle, spore structure and factors that influence the spore resistance of spore-forming Bacillus. Bacillus atrophaeus was used as reference microorganism for this review because their spores are widely used to study spore resistance and morphology. Understanding the mechanisms involved in the cell cycle and spore survival is important for developing strategies for spore killing; producing highly resistant spores for biodefense, food and pharmaceutical applications; and developing new bioactive molecules and methods for spore surface display.

Evaluation and improvement of air quality in school public elevator

Public elevators are an essential requirement in modern high-rise buildings. However, the confined, crowded interior of an elevator provides an ideal breeding ground for all manners of biological aerosols. Consequently, when using an elevator at a university in Taiwan as the research target, this study performs an experimental investigation into the effectiveness of hand-sprayed gaseous chlorine dioxide as a disinfection agent. The air quality before and after disinfection is evaluated by measuring the bioaerosol concentrations of bacteria and fungi, respectively. The average background levels of bacteria and fungi before disinfection are found to be 635.7 ± 469.6 and 1296.8 ± 966.6 colony-forming unit (CFU)/m(3), respectively. Following disinfection, the bacteria and fungi concentrations reduced by an average of 35 and 25 %, respectively. The multivariate analysis of variance (MANOVA) results showed that the residual bacteria and fungi concentration levels were determined primarily by the number of individuals within the elevator and the elapsed time following disinfection. In general, the present results show that given a maximum of five individuals within the elevator, a disinfection schedule of once every 40 min is sufficient to reduce the bioaerosol concentrations of bacteria and fungi to the levels specified by the Taiwan Environmental Protection Agency (EPA).