Surface, Water and Air Biocharacterization - A Comprehensive Characterization of Microorganisms and Allergens in Spacecraft Environment (SWAB) - 10.21.15

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
A Comprehensive Characterization of Microorganisms and Allergens in Spacecraft (SWAB) uses advanced molecular techniques to comprehensively evaluate microbes on board the International Space Station (ISS), including pathogens (organisms that may cause disease). SWAB also tracks changes in the microbial community as spacecrafts visit the station and new station modules are added. This study assesses the risk of microbes to the crew and the spacecraft.
Science Results for Everyone
Where humans go, microorganisms follow – even into space. A crew’s risk of infectious disease depends on both the concentration and characteristics of microorganisms. This experiment tested molecular techniques against traditional culture medium methods of evaluating microbes on the International Space Station (ISS). Both methods provided similar results, indicating that current efforts do not miss medically significant bacteria and fungi. Researchers identified 17 mold species in dust samples from ISS air filters, although mold has caused no known health effects to date. Molecular techniques show potential for spacecraft microbial monitoring, but sample preparation and data analysis present challenges.

The following content was provided by Duane L. Pierson, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details


Principal Investigator(s)
Duane L. Pierson, Ph.D., Johnson Space Center, Houston, TX, United States

Mark P. Buttner, Ph.D., University of Nevada, Las Vegas, Las Vegas, NV, United States
Patricia Cruz, Ph.D., University of Nevada, Las Vegas, Las Vegas, NV, United States
Charlie Mark Ott, Ph.D., Johnson Space Center, Houston, TX, United States

NASA Johnson Space Center, Human Research Program, Houston, TX, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)

Research Benefits
Information Pending

ISS Expedition Duration 1
April 2006 - April 2008; April 2009 - March 2010

Expeditions Assigned

Previous ISS Missions
SWAB has been performed on ISS Expedition 13, 14, 15, 16, 19, and 20.

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Experiment Description

Research Overview

  • Previous microbial analysis of spacecraft only identifies microorganisms that grow in culture, omitting greater than 90 percent of all microorganisms including pathogens such as Legionella (the bacterium which causes Legionnaires' disease) and Cryptosporidium (a parasite common in contaminated water).

  • Scientists have yet to study the incidence of potent allergens, such as dust mites and microbial toxins in spacecraft environments.

  • This study uses modern molecular techniques to identify microorganisms and allergens. Direct sampling of the ISS allows identification of the microbial communities present, and determination of whether these change or mutate over time.

  • SWAB complements the nominal ISS environmental monitoring by providing a comparison of analyses from current media-based and advanced molecular-based technologies.

During long-duration space flight missions, spacecrafts build up a diverse array of microorganisms that directly interacts with the crew. Most microorganisms are harmless or even beneficial to the crew; however, the presence of medically significant organisms appearing in this environment could adversely affect crew health and performance during long-duration missions. The primary goal of the Surface, Water and Air Biocharacterization–A Comprehensive Characterization of Microorganisms and Allergen in Spacecraft (SWAB) experiment is to use advanced technologies to better understand the types of organisms that the crew encounters, their sources, and assess the potential risks.

This study of microorganisms, allergens, and microbial toxins in the spacecraft environment mitigates the risk to the health, safety, and performance of crewmembers during flight. All previous methods evaluating spacecraft ecology utilize culture-based methodology; thus many organisms are omitted from isolation, including medically significant organisms, such as the pathogen Legionella (the bacteria that causes Legionnaire's disease). Likewise, culturable bacteria and fungi are the only potential allergens studied; the more potent allergens, such as dust mites, are not analyzed in spacecraft environments. This study utilizes modern molecular biology, advanced microscopy, and immunochemical techniques to examine air, surface, and water samples for bacteria and fungi, pathogenic protozoa, allergens, and microbial toxins.

New collection techniques improve the quality of the sample being returned from ISS for analysis. Air samples are collected through a novel gelatin filter to improve collection efficiency. These filters retain particles as small as viruses. Water and surface samples improve deoxyribonucleic acid (DNA) recovery using a DNA preservative that is composed of a mixture of sodium dodecylsulfate (SDS) and ethylenediaminetetraacetic acid (EDTA) in tris (hydroxymethyl) aminomethane (Tris) (an organic compound used as a component of buffer solutions) buffer.

Analysis of the in flight samples focus around molecular techniques. These include bacterial fingerprinting, bacterial and fungal ribosomal identification, and quantitative PCR (polymerase chain reaction) to identify and enumerate specific genes in environmental samples. The identification of specific genes is critical in the assessment of microorganisms for particular characteristics, including the production of microbial toxins. The samples returned from flight are evaluated using Denaturing Gradient Gel Electrophoresis (DGGE), a technique that allows identification of the bacteria without any amplification of the organisms with growth on media. This technique holds the potential to increase the number of different identified species by 100 fold.

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Space Applications
Knowing the microorganisms that the crew encounter is crucial in assessing the health risks of the crew and performance of the spacecraft systems. By studying the types of organisms and the change in this ecosystem over time, preventative and disinfection regiments are developed to mitigate the accumulation of medically significant organisms or microorganisms that foul filters or degrade components of the spacecraft.

Earth Applications
The results of this study provide insight into changes that occur in the microbial ecology of semi-closed systems. The development of specific primers for bacterial enumeration and fungal identification during this study advance the ability of ground-based investigators to diagnose the potential sources of microbial contamination and give insight into the causes of health related microbial contamination issues such as "sick building syndrome."

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Operational Requirements
The SWAB flight hardware requires no station power. Only the air sampler requires battery power. The new collection techniques are designed to require approximately the same amount of time as the current environmental monitoring; approximately 240 minutes. Data is recorded on the archival bags and no biohazardous trash is created.

Operational Protocols
Preflight surface and air samples are collected from all launch vehicles and ISS modules traveling to ISS. The samples collected are obtained by the investigation team. Air and surface samples are collected from a diverse range of locations in the vehicle or module at Launch minus 15 (L-15) or 15 to 20 days prior to hatch closure. A mixture of new locations and previously sampled locations are selected on a case-by-case basis determined by the investigator team. Collection of inflight air and surface samples from ISS occurs prior to every vehicle docking to ISS. Four air samples and twelve surface samples are collected during each collection session. Any surface condensation is collected, if available. The SWAB Return Kit containing in flight samples returns on each subsequent Space Shuttle flight. The time, humidity, and temperature of the ISS are monitored during the in-flight operations. Two water-samples (one hot and one ambient) are obtained every four weeks from the Potable Water Dispenser (PWD) in the U.S. Lab.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

The determination of risk from infectious disease during space flight missions is composed of several factors including both the concentration and characteristics of the microorganisms to which the crew are exposed. Thus, having a good understanding of the microbial ecology aboard spacecraft provides the necessary information to mitigate health risks to the crew. While stringent steps are taken to minimize the presence of pathogens on spacecraft, medically significant organisms have been isolated from both the Mir and International Space Station (ISS). Historically, the method for isolation and identification of microorganisms from spacecraft environmental samples depended upon their growth on culture media. Unfortunately, only a fraction of the organisms may grow on a specific culture medium, potentially omitting those microorganisms whose nutritional and physical requirements for growth are not met. To address this bias in our understanding of the ISS environment, the Surface, Water, and Air Biocharacterization (SWAB) Flight Experiment was designed to investigate and develop advanced monitoring technology to better characterize the ISS environment.

For the SWAB flight experiment, it was hypothesized that environmental analysis using non-culture-based technologies would reveal microorganisms, allergens, and microbial toxins not previously reported in spacecraft, allowing for a more complete health assessment. Key findings during this experiment included:


  • Sample analyses using the culture-based and advanced molecular methodology provided similar results, indicating the current monitoring methods are not “missing” medically significant bacteria and fungi. Dust samples taken from the HEPA air filters identified 17 different microbial mold species, most commonly P. chrysogenum and A. pullulans. Other opportunistic pathogens were also detected including a particularly high concentration of A. flavus and A. niger. Fortunately, to date there have been no known health effects from mold as a result of living aboard the ISS (Vesper et al 2008).

  • Molecular techniques have tremendous potential for microbial monitoring; however, sample preparation and data analysis present challenges for space flight hardware.

  • Analysis results indicate that some molecular techniques, such as denaturing gradient gel electrophoresis (DGGE), can be much less sensitive than culture-based methods, and More sensitive molecular techniques, such as quantitative polymerase chain reaction (QPCR), were able to identify viral DNA from ISS environments, suggesting potential transfer of the organism between crewmembers.

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Results Publications

    Vesper SJ, Wong W, Kuo CM, Pierson DL.  Mold species in dust from the International Space Station identified and quantified by mold-specific quantitative PCR. Research in Microbiology. 2008 July; 159(6): 432-435. DOI: 10.1016/j.resmic.2008.06.001.

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Ground Based Results Publications

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ISS Patents

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Related Publications

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Related Websites
Science@NASA - Preventing "Sick" Spaceships

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image NASA Image: ISS010E11563 - An example of contamination that has developed on one of the interior panels aboard ISS. This image shows how contamination can form on interior ISS surfaces. Crews have weekly sessions to clean ISS surfaces. SWAB will help us understand the microbes involved in contamination and how to deal with them.
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image The air sampling device used for the SWAB experiment, which collects air through a gelatin filter and can retain particles as small as viruses. Image courtesy of NASA.
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image Dust mites collected on a previous human space flight.
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image NASA Image: ISS013E80083 - Expedition 13 European Astronaut Thomas Reiter collects surface samples for the SWAB experiment prior to the arrival of STS-115.
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image NASA Image: ISS013E80070 - Expedition 13 ESA Astronaut Thomas Reiter prepares the air sampler to take samples for the SWAB experiment prior to the arrival of STS-115.
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image NASA Image: ISS015E07583 - Expeditions 14 and 15 Astronaut and Flight Engineer (FE-2), Sunita Williams, during setup for the Surface, Water and Air Biocharacterization (SWAB) experiment in the U.S. Laboratory/Destiny
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image NASA Image: ISS0515E07586 - Astronaut Sunita L. Williams, Expeditions 14 and 15 flight engineer, conducts a Surface, Water and Air Biocharacterization (SWAB) air sampling in the Destiny laboratory of the International Space Station.
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image NASA Image: ISS020E031558 - NASA astronaut Michael Barratt, Expedition 20 flight engineer, conducts a Surface, Water and Air Biocharacterization (SWAB) water sampling from the Potable Water Dispenser (PWD) in the Destiny laboratory of the International Space Station.
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image NASA Image: ISS033E005529 - Photo is of SWAB (Surface,Water and Air Biocharacterization) Air Sampling Device (ASD) on locker.
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