National validation study of a swab protocol for the recovery of Bacillus anthracis spores from surfaces

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.

Monitoring spore washoff during a biological contamination incident response using automated stormwater samplers and sensors to predict contamination movement

This study examined the washoff of Bacillus globigii (Bg) spores from concrete, asphalt, and grass surfaces by stormwater. Bg is a nonpathogenic surrogate for Bacillus anthracis, which is a biological select agent. Areas (2.74 m × 7.62 m) of concrete, grass, and asphalt were inoculated twice at the field site during the study. Spore concentrations were measured in runoff water after seven rainfall events (1.2-65.4 mm) and complimentary watershed data were collected for soil moisture, depth of water in collection troughs, and rainfall using custom-built telemetry units. An average surface loading of 107.79 Bg spores/m2 resulted in peak spore concentrations in runoff water of 102, 260, and 4.1 CFU/mL from asphalt, concrete, and grass surfaces, respectively. Spore concentrations in the stormwater runoff were greatly reduced by the third rain event after both inoculations, but still detectable in some samples. When initial rainfall events occurred longer after the initial inoculation, the spore concentrations (both peak and average) in the runoff were diminished. The study also compared rainfall data from 4 tipping bucket rain gauges and a laser disdrometer and found they performed similarly for values of total rainfall accumulation while the laser disdrometer provided additional information (total storm kinetic energy) useful in comparing the seven different rain events. The soil moisture probes are recommended for assistance in predicting when to sample sites with intermittent runoff. Sampling trough level readings were critical to understanding the dilution factor of the storm event and the age of the sample collected. Collectively the spore and watershed data are useful for emergency responders faced with remediation decisions after a biological agent incident as the results provide insight into what equipment to deploy and that spores may persist in runoff water at quantifiable levels for months. The spore measurements are also a novel dataset for stormwater model parameterization for biological contamination of urban watersheds.

Methods for virus recovery from environmental surfaces to monitor infectious viral contamination

Accurate quantification of infectious contaminants on environmental surfaces, particularly infectious viruses, is essential for contact transmission risk assessment; however, difficulties in recovering viruses from surfaces using swabs complicates this quantification process. Herein, we identified the factors that significantly affected virus recovery rates and developed an ideal swab method that yielded the highest rate of virus recovery. We comprehensively analyzed the effects of swab type (cotton/polyester), swab water content (wet/dry conditions), surface material, and surface area on the rates of viral RNA and infectious virus recovery. The virus recovery rate was significantly lower than the viral RNA recovery rate (P < 0.01), indicating difficulty in the quantification of infectious viruses. The virus recovery rate was significantly higher under wet conditions than that under dry conditions (P < 0.006), and the virus recovery rate obtained using cotton swabs was significantly higher than that using polyester swabs (P < 0.0001). Furthermore, the virus recovery rate had a strong negative correlation (correlation coefficient >0.8) with the target surface area. The maximum surface area where the virus recovery rate was ≥10% (MSA-10%) was identified as the maximum quantifiable area. For influenza virus recovery, MSA-10% on polyvinyl chloride (PVC) sheet, PVC leather, stainless steel, silicone, glass, and polycarbonate surfaces was 66.7, 193, 60.2, 144, 105, and 15.6 cm2, respectively. For feline calicivirus recovery, MSA-10% on PVC sheet, PVC leather, stainless steel, silicone, glass, and polycarbonate surfaces was 210, 111, 2120, 250, 322, and 180 cm2, respectively. The most accurate and ideal method for quantifying infectious viruses on environmental surfaces with the highest recovery rates meets three specifications: "wet conditions," "the use of cotton swabs," and "a target surface area of approximately 10 cm2.

Comparison of surface sampling methods for an extended duration outdoor biological contamination study

Bacillus anthracis, the causative agent for anthrax, is a dangerous pathogen to humans and has a history as a bioterrorism agent. While sampling methods have been developed and evaluated for characterizing and clearing contaminated indoor sites, the performance of these sampling methods is unknown for use in outdoor environments. This paper presents surface sampling data for Bacillus atrophaeus spores, a surrogate for B. anthracis, from a 210-day outdoor study that evaluated the detection and recovery of spores using five different sampling methods as follows: sponge sticks, 37-mm vacuum filter cassettes, residential wet vacuums, robotic floor cleaners, and grab samples of soil, leaves, and grass. The spores were applied by spraying a liquid suspension onto the surfaces. Both asphalt and concrete surfaces were sampled by all the surface sampling methods, excluding grab sampling. Stainless steel coupons placed outdoors were additionally sampled using sponge sticks. Sampling methods differed in their ability to collect detectable spores over the duration of the study. The 37-mm vacuums and sponge sticks consistently detected spores on asphalt through day 37 and robots through day 99. The wet vacuums detected spores on asphalt for days 1 and 4, but not again until day 210. On concrete, all samplers detected spores until day 210 except for sponge stick samplers that detected spores only up until the day 99 time point. For all sampling methods, spore recoveries were higher from concrete than from asphalt surfaces. There was no statistically significant difference in recoveries of sponge sticks and 37-mm vacuums from either asphalt or concrete surfaces. Processing of grab samples was challenging due to non-target background microorganisms resulting in high detection limits for the samples.

Development and Comparison of Complementary Methods to Study Potential Skin and Inhalational Exposure to Pathogens During Personal Protective Equipment Doffing

BACKGROUND

Fluorescent tracers are often used with ultraviolet lights to visibly identify healthcare worker self-contamination after doffing of personal protective equipment (PPE). This method has drawbacks, as it cannot detect pathogen-sized contaminants nor airborne contamination in subjects' breathing zones.

METHODS

A contamination detection/quantification method was developed using 2-µm polystyrene latex spheres (PSLs) to investigate skin contamination (via swabbing) and potential inhalational exposure (via breathing zone air sampler). Porcine skin coupons were used to estimate the PSL swabbing recovery efficiency and limit of detection (LOD). A pilot study with 5 participants compared skin contamination levels detected via the PSL vs fluorescent tracer methods, while the air sampler quantified potential inhalational exposure to PSLs during doffing.

RESULTS

Average PSL skin swab recovery efficiency was 40% ± 29% (LOD = 1 PSL/4 cm2 of skin). In the pilot study, all subjects had PSL and fluorescent tracer skin contamination. Two subjects had simultaneously located contamination of both types on a wrist and hand. However, for all other subjects, the PSL method enabled detection of skin contamination that was not detectable by the fluorescent tracer method. Hands/wrists were more commonly contaminated than areas of the head/face (57% vs 23% of swabs with PSL detection, respectively). One subject had PSLs detected by the breathing zone air sampler.

CONCLUSIONS

This study provides a well-characterized method that can be used to quantitate levels of skin and inhalational contact with simulant pathogen particles. The PSL method serves as a complement to the fluorescent tracer method to study PPE doffing self-contamination.

In Situ Visualization of Particle Motions during Wipe Sampling of Explosives and Other Trace Particulate Materials

Surface texture tailoring has the potential to increase the effectiveness of dry particle collection wipes, as a wipe's topographical features control the intimate surface contact made with particles on the substrate (critical for van der Waals-governed adhesion). However, texture-tailoring approaches have not yet been widely explored, in part because of a lack of understanding of the specific wipe topographies and wipe/particle interactions that maximize particle collection. Here we describe an in situ optical microscopy technique that enables direct observation of micrometer-scale particle-wipe interactions occurring at the wipe-substrate interface during contact sampling. The technique is demonstrated for nonwoven meta-aramid (Nomex) collection wipes with particles ranging from 1 to 90 μm in diameter and substrates of different topographies (glass and nylon coil zipper). Experiments with hemispherically coated Janus particles allow rolling motions to be distinguished from sliding motions, providing detailed information about how particles move prior to capture or release by the wipe. Particle-fiber and particle-particle interactions are seen to play important roles in particle capture, suggesting that conventional sphere-on-plane models are inadequate to describe adhesion behavior in these systems. Micrographs show how loose, flexible fibers in roughened textile wipes interrogate the valleys of uneven substrate topographies, allowing capture of particles that might otherwise be trapped within the substrate's grooves and depressions. The materials used in this work are specifically relevant to explosives detection, but the in situ visualization technique is transferable for the study of any application involving dry particle collection, such as toxic substance sampling and dust removal.

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 nylon-flocked swab and cellulose sponge methods for carbapenem-resistant Enterobacteriaceae and gram-negative organism recovery from high-touch surfaces in patient rooms

The ideal sampling method and benefit of qualitative versus quantitative culture for carbapenem-resistant Enterobacteriaceae (CRE) recovery in hospitalized patient rooms and bathrooms is unknown. Although the use of nylon-flocked swabs improved overall gram-negative organism recovery compared with cellulose sponges, they were similar for CRE recovery. Quantitative culture was inferior and unrevealing beyond the qualitative results.

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.

How well does transfer of bacterial pathogens by culture swabs correlate with transfer by hands?

In laboratory testing and in isolation rooms, pickup and transfer of health care-associated pathogens by premoistened rayon swabs correlated well with pickup and transfer by bare hands or moistened gloves. These results suggest that swab cultures provide a useful surrogate indicator of the risk for pathogen pickup and transfer by hands.

Evaluation of Commercial-off-the-Shelf Materials for the Preservation of Bacillus anthracis Vegetative Cells for Forensic Analysis

Environmental surface sampling is crucial in determining the zones of contamination and overall threat assessment. Viability retention of sampled material is central to such assessments. A systematic study was completed to determine viability of vegetative cells under nonpermissive storage conditions. Despite major gains in nucleic acid sequencing technologies, initial positive identification of threats must be made through direct culture of the sampled material using classical microbiological methods. Solutions have been developed to preserve the viability of pathogens contained within clinical samples, but many have not been examined for their ability to preserve biological agents. The purpose of this study was to systematically examine existing preservation materials that can retain the viability of Bacillus anthracis vegetative cells stored under nonpermissive temperatures. The results show effectiveness of five of seventeen solutions, which are capable of retaining viability of a sporulation deficient strain of B. anthracis Sterne when stored under nonrefrigerated conditions.

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.

Persistence of influenza on surfaces

BACKGROUND

Close contact transmission (either direct or large droplet/droplet nuclei) is considered the main driver of influenza outbreaks but there is limited information regarding the role of fomites in transmission.

AIM

To investigate the surface stability of influenza strains and thereby the role of fomites in transmission.

METHODS

The viability and quantitative reverse transcription-polymerase chain reaction (qt-RT-PCR) signal of five influenza strains (A/PR/8/34/H1N1, A/Cal/7/09/H1N1, A/Cal/4/09/H1N1, A/Sol/54/06/H1N1, and A/Bris/59/07/H1N1) seeded on to three surfaces (cotton, microfibre, and stainless steel) were assessed over time. Coupons of material were seeded with 10μL of a 10⁶-10⁸pfu/mL suspension of cell culture-derived virus stock supplemented with 0.3% bovine serum albumin. Coupons were assayed by plaque assay and qt-RT-PCR at 1, 24h, and weekly for seven weeks using a vortex-mixing elution method.

FINDINGS

Viable virus was detected from coupons for up to two weeks (stainless steel) and one week (cotton and microfibre), whereas detection of viruses by PCR was made for the entire seven-week study period. No strain differences were found. Ninety-nine percent reduction values (as a function of the seeding stock) were determined to be 17.7h for cotton (R²=0.86), 34.3h for microfibre (R²=0.80), and 174.9h for stainless steel (R²=0.98).

CONCLUSION

Viable influenza was recovered from surfaces for up to two weeks. By contrast, influenza could be detected by PCR for more than seven weeks. These results have important implications for determining infection control protocols, cleaning regimes and sampling methods in healthcare settings.

Extraction of Aerosol-Deposited Yersinia pestis from Indoor Surfaces To Determine Bacterial Environmental Decay

Public health and decontamination decisions following an event that causes indoor contamination with a biological agent require knowledge of the environmental persistence of the agent. The goals of this study were to develop methods for experimentally depositing bacteria onto indoor surfaces via aerosol, evaluate methods for sampling and enumerating the agent on surfaces, and use these methods to determine bacterial surface decay. A specialized aerosol deposition chamber was constructed, and methods were established for reproducible and uniform aerosol deposition of bacteria onto four coupon types. The deposition chamber facilitated the control of relative humidity (RH; 10 to 70%) following particle deposition to mimic the conditions of indoor environments, as RH is not controlled by standard heating, ventilation, and air conditioning (HVAC) systems. Extraction and culture-based enumeration methods to quantify the viable bacteria on coupons were shown to be highly sensitive and reproducible. To demonstrate the usefulness of the system for decay studies,Yersinia pestis persistence as a function of surface type at 21 °C and 40% RH was determined to be >40%/min for all surfaces. Based upon these results, at typical indoor temperature and RH, a 6-log reduction in titer would expected to be achieved within 1 h as the result of environmental decay on surfaces without active decontamination. The developed approach will facilitate future persistence and decontamination studies with a broad range of biological agents and surfaces, providing agent decay data to inform both assessments of risk to personnel entering a contaminated site and decontamination decisions following biological contamination of an indoor environment.

IMPORTANCE

Public health and decontamination decisions following contamination of an indoor environment with a biological agent require knowledge of the environmental persistence of the agent. Previous studies on Y. pestis persistence have utilized large liquid droplet deposition to provide persistence data. As a result, methods were developed to deposit aerosols containing bacteria onto indoor surfaces, reproducibly enumerate bacteria harvested from coupons, and determine surface decay utilizing Y. pestis The results of this study provide foundational methods required to evaluate surface decay of bacteria and potentially other biological agents, such as viruses, in aerosol particles as a function of surface type and environment. Integrating the data from both aerosol and liquid deposition surface decay studies will provide medical and public health personnel with a more complete understanding of agent persistence on surfaces in contaminated areas for assessment of health risks and to inform decontamination decisions.

False-negative rate, limit of detection and recovery efficiency performance of a validated macrofoam-swab sampling method for low surface concentrations of Bacillus anthracis Sterne and Bacillus atrophaeus spores

AIMS

We sought to evaluate the effects of Bacillus species, low surface concentrations, and surface material on recovery efficiency (RE), false-negative rate (FNR) and limit of detection for recovering Bacillus spores using a validated macrofoam-swab sampling procedure.

METHODS AND RESULTS

The performance of a macrofoam-swab sampling method was evaluated using Bacillus anthracis Sterne (BAS) and Bacillus atrophaeus Nakamura (BG) spores applied at nine low target surface concentrations (2 to 500 CFU per plate or coupon) to positive-control plates and test coupons (25·8064 cm(2) ) of four surface materials (glass, stainless steel, vinyl tile and plastic). The Bacillus species and surface material had statistically significant effects on RE, but surface concentration did not. Mean REs were the lowest for vinyl tile (50·8% with BAS and 40·2% with BG) and the highest for glass (92·8% with BAS and 71·4% with BG). FNR values (which ranged from 0 to 0·833 for BAS and from 0 to 0·806 for BG) increased as surface concentration decreased in the range tested. Surface material also had a statistically significant effect on FNR, with FNR the lowest for glass and highest for vinyl tile. Finally, FNR tended to be higher for BG than for BAS at lower surface concentrations, especially for glass.

CONCLUSIONS

Concentration and surface material had significant effects on FNR, with Bacillus species having a small effect. Species and surface material had significant effects on RE, with surface concentration having a nonsignificant effect.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results provide valuable information on the performance of the macrofoam-swab method for low surface concentrations of Bacillus spores, which can be adapted to assess the likelihood that there is no contamination when all macrofoam-swab samples fail to detect B. anthracis.

Evaluation of tools for environmental sampling of Bacillus anthracis spores

This study describes the validation of sampling techniques used to detect biological warfare agents used in terror attacks. For this purpose, we tested the efficiencies of different sampling media and extraction solutions for the recovery of bacterial pathogens. We first used Bacillus cereus ATCC 4342 spores as a surrogate for highly pathogenic B. anthracis to compare recovery efficiencies of spores from four different surfaces. We used three different types of sampling swabs and four different solutions to extract spores from the swabs. The most effective sampling method employed rayon swabs moistened with water. The efficencies of the four extraction solutions did not differ significantly, although yields were highest using phosphate-buffered saline containing Tween 80 (PBS-T). Using rayon swabs and sterile water, we recovered B. cereus ATCC 4342 and B. anthracis spores with equivalent efficiencies. These findings indicate that because of its reduced pathogenicity and relative ease in handling (Biosafety Level 1), use of B. cereus ATCC 4342 will facilitate further optimization of techniques to detect B. anthracis.

Development of an ELISA for evaluation of swab recovery efficiencies of bovine serum albumin

After a potential biological incident the sampling strategy and sample analysis are crucial for the outcome of the investigation and identification. In this study, we have developed a simple sandwich ELISA based on commercial components to quantify BSA (used as a surrogate for ricin) with a detection range of 1.32–80 ng/mL. We used the ELISA to evaluate different protein swabbing procedures (swabbing techniques and after-swabbing treatments) for two swab types: a cotton gauze swab and a flocked nylon swab. The optimal swabbing procedure for each swab type was used to obtain recovery efficiencies from different surface materials. The surface recoveries using the optimal swabbing procedure ranged from 0–60% and were significantly higher from nonporous surfaces compared to porous surfaces. In conclusion, this study presents a swabbing procedure evaluation and a simple BSA ELISA based on commercial components, which are easy to perform in a laboratory with basic facilities. The data indicate that different swabbing procedures were optimal for each of the tested swab types, and the particular swab preference depends on the surface material to be swabbed.

Vulnerability of Bacillus spores and of related genera to physical impaction injury with particular reference to spread-plating

AIMS

To examine whether bacterial spores are vulnerable to impaction injury during standard spread-plating or to other modes of physical impaction.

METHODS AND RESULTS

Employing heat-challenged spores of Bacillus pumilus, Bacillus subtilis, Bacillus thuringiensis, Lysinibacillus, Paenibacillus and Brevibacillus spp. from day-4 to day-10 nutrient agar (NA) plates in 50% ethanol, plating the spore suspension to the extent of just drying the agar surface on fresh NA (50-60 s; SP-B) was tested in comparison with the spreader-independent approach of spotting-and-tilt-spreading (SATS), or a brief plating (<10 s; SP-A). Spore CFU was significantly reduced with SP-B in different organisms (23-40%) over SATS independent of the spore size. Comparing 4-, 7- and 10-day-old B. pumilus spores, the former two displayed significant CFU reduction in SP-B indicating a spore age-related effect. Continuous plating for 2-5 min showed a reduction in spore CFU in all organisms depending on plating duration. CFU reduction effect with SP-B was less manifest on refrigerated plates where no friction was experienced but acute on prewarmed and surface-dried plates. Spreader movement over agar surface subsequent to the exhaustion of free moisture proved highly detrimental to spores. A simulated plating study by plating the spores over a plastic film till drying showed a significant reduction in spore CFU. DAPI staining and glass bead-vortexing studies confirmed spore disruption through physical impaction.

CONCLUSIONS

Bacterial spores are vulnerable to injury during spread-plating or with other forms of physical impaction with variable effects on different genotypes independent of the spore size but altered by spore age.

SIGNIFICANCE AND IMPACT OF THE STUDY

Implications during spore CFU estimations employing spread-plating and during spore surveillance, and the recommendation of SATS as an easier and safer alternative for spore CFU enumeration.

A genetic inventory of spacecraft and associated surfaces

Terrestrial organisms or other contaminants that are transported to Mars could interfere with efforts to study the potential for indigenous martian life. Similarly, contaminants that make the round-trip to Mars and back to Earth could compromise the ability to discriminate an authentic martian biosignature from a terrestrial organism. For this reason, it is important to develop a comprehensive inventory of microbes that are present on spacecraft to avoid interpreting their traces as authentic extraterrestrial biosignatures. Culture-based methods are currently used by NASA to assess spacecraft cleanliness but deliberately detect only a very small subset of total organisms present. The National Research Council has recommended that molecular (DNA)-based identification techniques should be developed as one aspect of managing the risk that terrestrial contamination could interfere with detection of life on (or returned from) Mars. The current understanding of the microbial diversity associated with spacecraft and clean room surfaces is expanding, but the capability to generate a comprehensive inventory of the microbial populations present on spacecraft outbound from Earth would address multiple considerations in planetary protection, relevant to both robotic and human missions. To this end, a 6-year genetic inventory study was undertaken by a NASA/JPL team. It was completed in 2012 and included delivery of a publicly available comprehensive final report. The genetic inventory study team evaluated the utility of three analytical technologies (conventional cloning techniques, PhyloChip DNA microarrays, and 454 tag-pyrosequencing) and combined them with a systematic methodology to collect, process, and archive nucleic acids as the first steps in assessing the phylogenetic breadth of microorganisms on spacecraft and associated surfaces.

Comparative evaluation of vacuum-based surface sampling methods for collection of Bacillus spores

In this study, four commonly-used sampling devices (vacuum socks, 37 mm 0.8 μm mixed cellulose ester (MCE) filter cassettes, 37 mm 0.3 μm polytetrafluoroethylene (PTFE) filter cassettes, and 3M™ forensic filters) were comparatively evaluated for their ability to recover surface-associated spores. Aerosolized spores (~10(5)CFUcm(-2)) of a Bacillus anthracis surrogate were allowed to settle onto three material types (concrete, carpet, and upholstery). Ten replicate samples were collected using each vacuum method, from each material type. Stainless steel surfaces, inoculated simultaneously with test materials, were sampled with pre-moistened wipes. Wipe recoveries were utilized to normalize vacuum-based recoveries across trials. Recovery (CFUcm(-2)) and relative recovery (vacuum recovery/wipe recovery) were determined for each method and material type. Recoveries and relative recoveries ranged from 3.8 × 10(3) to 7.4 × 10(4)CFUcm(-2) and 0.035 to 1.242, respectively. ANOVA results indicated that the 37 mm MCE method exhibited higher relative recoveries than the other methods when used for sampling concrete or upholstery. While the vacuum sock resulted in the highest relative recoveries on carpet, no statistically significant difference was detected. The results of this study may be used to guide selection of sampling approaches following biological contamination incidents.

Standardized, App-based disinfection of iPads in a clinical and nonclinical setting: comparative analysis

Background

With the use of highly mobile tools like tablet PCs in clinical settings, an effective disinfection method is a necessity. Since manufacturers do not allow cleaning methods that make use of anything but a dry fleece, other approaches have to be established to ensure patient safety and to minimize risks posed by microbiological contamination.

Objective

The ability of isopropanol wipes to decontaminate iPads was evaluated prospectively in a observer blinded, comparative analysis of devices used in a clinical and a nonclinical setting.

Methods

10 new iPads were randomly deployed to members of the nursing staff of 10 clinical wards, to be used in a clinical setting over a period of 4 weeks. A pre-installed interactive disinfection application (deBac-app, PLRI MedAppLab, Germany) was used on a daily basis. Thereafter, the number and species of remaining microorganisms on the surface of the devices (13 locations; front and back) was evaluated using contact agar plates. Following this, the 10 iPads were disinfected and randomly deployed to medical informatics professionals who also used the devices for 4 weeks but were forbidden to use disinfecting agents. The quality of a single, standardized disinfection process was then determined by a final surface disinfection process of all devices in the infection control laboratory. No personal data were logged with the devices. The evaluation was performed observer blinded with respect to the clinical setting they were deployed in and personnel that used the devices.

Results

We discovered a 2.7-fold (Mann-Whitney U test, z=-3.402, P=.000670) lower bacterial load on the devices used in the clinical environment that underwent a standardized daily disinfection routine with isopropanol wipes following the instructions provided by “deBac-app”. Under controlled conditions, an average reduction of the mainly Gram-positive normal skin microbiological load of 99.4% (Mann-Whitney U test, z=-3.1798, P=.001474) for the nonclinical group and 98.1% (Mann-Whitney U test, z=3.1808, P=.001469) for the clinical group was achieved using one complete disinfecting cycle.

Conclusions

Normal use of tablet PCs leads to a remarkable amount of microbial surface contamination. Standardized surface disinfection with isopropanol wipes as guided by the application significantly reduces this microbial load. When performed regularly, the disinfection process helps with maintaining a low germ count during use. This should reduce the risk of subsequent nosocomial pathogen transmission. Unfortunately, applying a disinfection procedure such as the one we propose may lead to losing the manufacturer’s warranty for the devices; this remains an unsolved issue.

Evaluation of surface sampling for Bacillus spores using commercially available cleaning robots

Five commercially available domestic cleaning robots were evaluated on their effectiveness for sampling aerosol-deposited Bacillus atrophaeus spores on different indoor material surfaces. The five robots tested include three vacuum types (R1, R2, and R3), one wet wipe (R4), and one wet vacuum (R5). Tests were conducted on two different surface types (carpet and laminate) with 10(6) colony forming units of B. atrophaeus spores deposited per coupon (35.5 cm × 35.5 cm). Spores were deposited on the center surface (30.5 × 30.5 cm) of the coupon's total surface area (71.5 × 71.5 cm), and the surfaces were sampled with an individual robot in an isolation chamber. Chamber air was sampled using a biofilter sampler to determine the potential for resuspension of spores during sampling. Robot test results were compared to currently used surface sampling methods (vacuum sock for carpet and sponge wipe for laminate). The test results showed that the average sampling efficacies for R1, R2, and R3 on carpet were 26, 162, and 92% of vacuum sock sampling efficacy, respectively. On laminate, R1, R2, R3, R4, and R5 average sampling efficacies were 8, 11, 2, 62, and 32% of sponge wipe sampling efficacy, respectively. We conclude that some robotic cleaners were as efficacious as the currently used surface sampling methods for B. atrophaeus spores on these surfaces.

A rapid and repeatable method to deposit bioaerosols on material surfaces

A simple method for repeatably inoculating surfaces with a precise quantity of aerosolized spores was developed. Laboratory studies were conducted to evaluate the variability of the method within and between experiments, the spatial distribution of spore deposition, the applicability of the method to complex surface types, and the relationship between material surface roughness and spore recoveries. Surface concentrations, as estimated by recoveries from wetted-wipe sampling, were between 5×10(3) and 1.5×10(4)CFUcm(-2) across the entire area (930cm(2)) inoculated. Between-test variability (Cv) in spore recoveries was 40%, 81%, 66%, and 20% for stainless steel, concrete, wood, and drywall, respectively. Within-test variability was lower, and did not exceed 33%, 47%, 52%, and 20% for these materials. The data demonstrate that this method is repeatable, is effective at depositing spores across a target surface area, and can be used to dose complex materials such as concrete, wood, and drywall. In addition, the data demonstrate that surface sampling recoveries vary by material type, and this variability can partially be explained by the material surface roughness index. This deposition method was developed for use in biological agent detection, sampling, and decontamination studies, however, is potentially beneficial to any scientific discipline that investigates surfaces containing aerosol-borne particles.

Detecting laboratory DNA contamination using polyester-rayon wipes: a method validation study

Due to the high sensitivity of many PCR assays, extraneous target DNA in a laboratory setting can lead to false positive results. To assess the presence of extraneous DNA, many laboratories use gauze wipes to sample laboratory surfaces. The accuracy, precision, limits of detection, linearity, and robustness of a wipe test method and each associated wipe processing step were evaluated using E. coli genomic DNA. The method demonstrated a limit of detection of 108 copies of DNA, which equates to detectable surface concentration of 4.5×10(5) copies of DNA per area sampled. Recovery efficiency or accuracy is 22±10% resulting from a >58% loss of DNA occurring at the wipe wash step. The method is robust, performing consistently despite deliberate modifications of the protocol.

Storage Effects on Sample Integrity of Environmental Surface Sampling Specimens with Bacillus anthracis Spores

The effect of packaging, shipping temperatures and storage times on recovery of Bacillus anthracis. Sterne spores from swabs was investigated. Macrofoam swabs were pre-moistened, inoculated with Bacillus anthracis spores, and packaged in primary containment or secondary containment before storage at -15°C, 5°C, 21°C, or 35°C for 0-7 days. Swabs were processed according to validated Centers for Disease Control/Laboratory Response Network culture protocols, and the percent recovery relative to a reference sample (T₀) was determined for each variable. No differences were observed in recovery between swabs held at -15° and 5°C, (p ≥ 0.23). These two temperatures provided significantly better recovery than swabs held at 21°C or 35°C (all 7 days pooled, p ≤ 0.04). The percent recovery at 5°C was not significantly different if processed on days 1, 2 or 4, but was significantly lower on day 7 (day 2 vs. 7, 5°C, 10², p=0.03). Secondary containment provided significantly better percent recovery than primary containment, regardless of storage time (5°C data, p ≤ 0.008). The integrity of environmental swab samples containing Bacillus anthracis spores shipped in secondary containment was maintained when stored at -15°C or 5°C and processed within 4 days to yield the optimum percent recovery of spores.

Improved recovery of Bacillus spores from nonporous surfaces with cotton swabs over foam, nylon, or polyester, and the role of hydrophilicity of cotton in governing the recovery efficiency

Evaluating different swabbing materials for spore recovery efficiency (RE) from steel surfaces, we recorded the maximum RE (71%) of 10(7) Bacillus subtilis spores with Tulips cotton buds, followed by Johnson's cotton buds and standard Hi-Media cotton, polyester, nylon, and foam (23%) swabs. Among cotton swabs, instant water-absorbing capacity or the hydrophilicity index appeared to be the major indicator of RE, as determined by testing three more brands. Tulips swabs worked efficiently across diverse nonporous surfaces and on different Bacillus spp., registering 65 to 77% RE.

Swab protocol for rapid laboratory diagnosis of cutaneous anthrax

The clinical laboratory diagnosis of cutaneous anthrax is generally established by conventional microbiological methods, such as culture and directly straining smears of clinical specimens. However, these methods rely on recovery of viable Bacillus anthracis cells from swabs of cutaneous lesions and often yield negative results. This study developed a rapid protocol for detection of B. anthracis on clinical swabs. Three types of swabs, flocked-nylon, rayon, and polyester, were evaluated by 3 extraction methods, the swab extraction tube system (SETS), sonication, and vortex. Swabs were spiked with virulent B. anthracis cells, and the methods were compared for their efficiency over time by culture and real-time PCR. Viability testing indicated that the SETS yielded greater recovery of B. anthracis from 1-day-old swabs; however, reduced viability was consistent for the 3 extraction methods after 7 days and nonviability was consistent by 28 days. Real-time PCR analysis showed that the PCR amplification was not impacted by time for any swab extraction method and that the SETS method provided the lowest limit of detection. When evaluated using lesion swabs from cutaneous anthrax outbreaks, the SETS yielded culture-negative, PCR-positive results. This study demonstrated that swab extraction methods differ in their efficiency of recovery of viable B. anthracis cells. Furthermore, the results indicated that culture is not reliable for isolation of B. anthracis from swabs at ≥ 7 days. Thus, we recommend the use of the SETS method with subsequent testing by culture and real-time PCR for diagnosis of cutaneous anthrax from clinical swabs of cutaneous lesions.

Laboratory studies on surface sampling of Bacillus anthracis contamination: summary, gaps and recommendations

This article summarizes previous laboratory studies to characterize the performance of methods for collecting, storing/transporting, processing and analysing samples from surfaces contaminated by Bacillus anthracis or related surrogates. The focus is on plate culture and count estimates of surface contamination for swab, wipe and vacuum samples of porous and nonporous surfaces. Summaries of the previous studies and their results were assessed to identify gaps in information needed as inputs to calculate key parameters critical to risk management in biothreat incidents. One key parameter is the number of samples needed to make characterization or clearance decisions with specified statistical confidence. Other key parameters include the ability to calculate, following contamination incidents, the (i) estimates of B. anthracis contamination, as well as the bias and uncertainties in the estimates and (ii) confidence in characterization and clearance decisions for contaminated or decontaminated buildings. Gaps in knowledge and understanding identified during the summary of the studies are discussed. Additional work is needed to quantify (i) the false-negative rates of surface-sampling methods with lower concentrations on various surfaces and (ii) the effects on performance characteristics of: aerosol vs liquid deposition of spores, using surrogates instead of B. anthracis, real-world vs laboratory conditions and storage and transportation conditions. Recommendations are given for future evaluations of data from existing studies and possible new studies.

Impact of processing method on recovery of bacteria from wipes used in biological surface sampling

Environmental sampling for microbiological contaminants is a key component of hygiene monitoring and risk characterization practices utilized across diverse fields of application. However, confidence in surface sampling results, both in the field and in controlled laboratory studies, has been undermined by large variation in sampling performance results. Sources of variation include controlled parameters, such as sampling materials and processing methods, which often differ among studies, as well as random and systematic errors; however, the relative contributions of these factors remain unclear. The objective of this study was to determine the relative impacts of sample processing methods, including extraction solution and physical dissociation method (vortexing and sonication), on recovery of Gram-positive (Bacillus cereus) and Gram-negative (Burkholderia thailandensis and Escherichia coli) bacteria from directly inoculated wipes. This work showed that target organism had the largest impact on extraction efficiency and recovery precision, as measured by traditional colony counts. The physical dissociation method (PDM) had negligible impact, while the effect of the extraction solution was organism dependent. Overall, however, extraction of organisms from wipes using phosphate-buffered saline with 0.04% Tween 80 (PBST) resulted in the highest mean recovery across all three organisms. The results from this study contribute to a better understanding of the factors that influence sampling performance, which is critical to the development of efficient and reliable sampling methodologies relevant to public health and biodefense.

False-negative rate and recovery efficiency performance of a validated sponge wipe sampling method

Recovery of spores from environmental surfaces varies due to sampling and analysis methods, spore size and characteristics, surface materials, and environmental conditions. Tests were performed to evaluate a new, validated sponge wipe method using Bacillus atrophaeus spores. Testing evaluated the effects of spore concentration and surface material on recovery efficiency (RE), false-negative rate (FNR), limit of detection (LOD), and their uncertainties. Ceramic tile and stainless steel had the highest mean RE values (48.9 and 48.1%, respectively). Faux leather, vinyl tile, and painted wood had mean RE values of 30.3, 25.6, and 25.5, respectively, while plastic had the lowest mean RE (9.8%). Results show roughly linear dependences of RE and FNR on surface roughness, with smoother surfaces resulting in higher mean REs and lower FNRs. REs were not influenced by the low spore concentrations tested (3.10 × 10(-3) to 1.86 CFU/cm(2)). Stainless steel had the lowest mean FNR (0.123), and plastic had the highest mean FNR (0.479). The LOD(90) (≥1 CFU detected 90% of the time) varied with surface material, from 0.015 CFU/cm(2) on stainless steel up to 0.039 on plastic. It may be possible to improve sampling results by considering surface roughness in selecting sampling locations and interpreting spore recovery data. Further, FNR values (calculated as a function of concentration and surface material) can be used presampling to calculate the numbers of samples for statistical sampling plans with desired performance and postsampling to calculate the confidence in characterization and clearance decisions.

National validation study of a cellulose sponge wipe-processing method for use after sampling Bacillus anthracis spores from surfaces

This work was initiated to address the gaps identified by Congress regarding validated biothreat environmental sampling and processing methods. Nine Laboratory Response Network-affiliated laboratories participated in a validation study of a cellulose sponge wipe-processing protocol for the recovery, detection, and quantification of viable Bacillus anthracis Sterne spores from steel surfaces. Steel coupons (645.16 cm(2)) were inoculated with 1 to 4 log(10) spores and then sampled with cellulose sponges (Sponge-Stick; 3M, St. Paul, MN). Surrogate dust and background organisms were added to the sponges to mimic environmental conditions. Labs processed the sponges according to the provided protocol. Sensitivity, specificity, and mean percent recovery (%R), between-lab variability, within-lab variability, and total percent coefficient of variation were calculated. The mean %R (standard error) of spores from the surface was 32.4 (4.4), 24.4 (2.8), and 30.1 (2.3) for the 1-, 2-, and 4-log(10) inoculum levels, respectively. Sensitivities for colony counts were 84.1%, 100%, and 100% for the 1-, 2-, and 4-log(10) inocula, respectively. These data help to characterize the variability of the processing method and thereby enhance confidence in the interpretation of the results of environmental sampling conducted during a B. anthracis contamination investigation.

Rapid-viability PCR method for detection of live, virulent Bacillus anthracis in environmental samples

In the event of a biothreat agent release, hundreds of samples would need to be rapidly processed to characterize the extent of contamination and determine the efficacy of remediation activities. Current biological agent identification and viability determination methods are both labor- and time-intensive such that turnaround time for confirmed results is typically several days. In order to alleviate this issue, automated, high-throughput sample processing methods were developed in which real-time PCR analysis is conducted on samples before and after incubation. The method, referred to as rapid-viability (RV)-PCR, uses the change in cycle threshold after incubation to detect the presence of live organisms. In this article, we report a novel RV-PCR method for detection of live, virulent Bacillus anthracis, in which the incubation time was reduced from 14 h to 9 h, bringing the total turnaround time for results below 15 h. The method incorporates a magnetic bead-based DNA extraction and purification step prior to PCR analysis, as well as specific real-time PCR assays for the B. anthracis chromosome and pXO1 and pXO2 plasmids. A single laboratory verification of the optimized method applied to the detection of virulent B. anthracis in environmental samples was conducted and showed a detection level of 10 to 99 CFU/sample with both manual and automated RV-PCR methods in the presence of various challenges. Experiments exploring the relationship between the incubation time and the limit of detection suggest that the method could be further shortened by an additional 2 to 3 h for relatively clean samples.

Parameters affecting spore recovery from wipes used in biological surface sampling

The need for the precise and reliable collection of potential biothreat contaminants has motivated research in developing a better understanding of the variability in biological surface sampling methods. In this context, the objective of this work was to determine parameters affecting the efficiency of extracting Bacillus anthracis Sterne spores from commonly used wipe sampling materials and to describe performance using the interfacial energy concept. In addition, surface thermodynamics was applied to understand and predict surface sampling performance. Wipe materials were directly inoculated with known concentrations of B. anthracis spores and placed into extraction solutions, followed by sonication or vortexing. Experimental factors investigated included wipe material (polyester, cotton, and polyester-rayon), extraction solution (sterile deionized water [H(2)O], deionized water with 0.04% Tween 80 [H(2)O-T], phosphate-buffered saline [PBS], and PBS with 0.04% Tween 80 [PBST]), and physical dissociation method (vortexing or sonication). The most efficient extraction from wipes was observed for solutions containing the nonionic surfactant Tween 80. The increase in extraction efficiency due to surfactant addition was attributed to an attractive interfacial energy between Tween 80 and the centrifuge tube wall, which prevented spore adhesion. Extraction solution significantly impacted the extraction efficiency, as determined by statistical analysis (P < 0.05). Moreover, the extraction solution was the most important factor in extraction performance, followed by the wipe material. Polyester-rayon was the most efficient wipe material for releasing spores into solution by rank; however, no statistically significant difference between polyester-rayon and cotton was observed (P > 0.05). Vortexing provided higher spore recovery in H(2)O and H(2)O-T than sonication, when all three wipe materials and the reference control were considered (P < 0.05).

Evaluation of procedures for the collection, processing, and analysis of biomolecules from low-biomass surfaces

To comprehensively assess microbial diversity and abundance via molecular-analysis-based methods, procedures for sample collection, processing, and analysis were evaluated in depth. A model microbial community (MMC) of known composition, representative of a typical low-biomass surface sample, was used to examine the effects of variables in sampling matrices, target cell density/molecule concentration, and cryogenic storage on the overall efficacy of the sampling regimen. The MMC used in this study comprised 11 distinct species of bacterial, archaeal, and fungal lineages associated with either spacecraft or clean-room surfaces. A known cellular density of MMC was deposited onto stainless steel coupons, and after drying, a variety of sampling devices were used to recover cells and biomolecules. The biomolecules and cells/spores recovered from each collection device were assessed by cultivable and microscopic enumeration, and quantitative and species-specific PCR assays. rRNA gene-based quantitative PCR analysis showed that cotton swabs were superior to nylon-flocked swabs for sampling of small surface areas, and for larger surfaces, biological sampling kits significantly outperformed polyester wipes. Species-specific PCR revealed differential recovery of certain species dependent upon the sampling device employed. The results of this study empower current and future molecular-analysis-based microbial sampling and processing methodologies.