The Microbiome: The Forgotten Organ of the Astronaut's Body — Probiotics Beyond Terrestrial Limits

Amir Ata Saei; Abolfazl Barzegari

Future Microbiol. 2012;7(9):1037-1046.

The Human Intestine & the Microbiome

Today 'gut health' is a term increasingly used in the medical literature to describe effective digestion and absorption, the absence of gastrointestinal lesions, presence of normal intestinal microflora and proper immune function.^[5] However, from a scientific point of view, it is still extremely unclear what gut health is or how it can be defined and/or measured. The interactions between the gastrointestinal barrier and the microbiome appear to be a complex mechanism that assists in maintaining gut health. The gastrointestinal tract contributes to digestion and absorption of nutrients, minerals and fluids, osmoregulation, endocrine regulation and host metabolism, mucosal and systemic tolerance, immunoenhancement, defense against potential pathogens and harmful substances, signaling from the periphery to the brain, and detoxification of toxic molecules originating from the environment or the host.^[6] Recognition of the importance of gastrointestinal health and microflora can be an important asset to astronauts' health.

Across the large surface of the digestive tract, healthy and pathogenic bacteria compete for dominance. With such a huge exposure area, the immune system has a hard task of hindering pathogens from entering the blood and lymph. The presence of a balance between beneficial and potentially harmful bacteria is considered normal and contributes to a dynamic and healthy human gut. One way to maintain this homeostasis is to introduce helpful bacteria or probiotics. After the first suggestion of the health benefits of probiotics in the early 20th century by Nobel Laureate Metchnikoff, many bacterial strains have been clinically tested as potential probiotics.^[7] Probiotics are thought to play a health-promoting role by improving intestinal microbial infections.^[8–10] The surface area, apparent balance of microflora and health impact of the human gut reminds us that this complex organ must not be forgotten as one factor in long-duration spaceflight health.

1 2 3 4 5 6

Next Section

Abstract and Introduction
The Human Intestine & the Microbiome
Stress & Gut Microbiome
Microgravity Stress Alters Bacterial Virulence
Spaceflight & the Microbiome
Future Perspective: Considering Probiotics as a Countermeasure
References
Sidebar

Sidebar

Executive Summary

Establishment of Efficient Life Support Systems in Space

Designing an efficient life support system is needed to maintain the minimum life requirements for humans in space.
Although the health status of astronauts has been extensively investigated, less attention has been paid to the intestinal microbiome and its significant role in the astronaut's health.

The Human Intestine & the Microbiome

At the end of the Human Genome Project, the aggregation of flora genes within the human genome was named the 'human metagenome'.
A healthy gut seems to require a natural combination of healthy and pathogenic microflora, such that the certain resident microflora strains are now being characterized as a microbiome: cells essential in the maintenance of human health.
The human gut microbiome is implicated in human health and disease.
The microbiome plays key roles in maintenance of a healthy immune system.

Stress & Gut Microbiome

Spaceflight has several important disrupting events that could lead to astronaut intestinal changes: the sterility of space food, the changes in lifestyle, the possible use of antibiotics preflight and inflight, and changes in astronaut immune function.

Microgravity Stress Alters Bacterial Virulence

Microgravity seems to alter the availability and virulence of some pathogens.
A number of pathogens exhibit enhanced antibiotic resistance in microgravity.
It has been hypothesized that reduction in the natural, terrestrial diversity of the gastrointestinal microflora in spaceflight may give rise to an increase in the presence of the drug-resistant bacteria.
It has been postulated that the emergence of resistant clones could be facilitated by the administration of antibiotics, either before or during the flight.
Emergence of drug resistance is also facilitated by bacterial mutations which occur more frequently in space.

Spaceflight & the Microbiome

A reduction in the number and/or diversity of beneficial gut microbiota can lead to an increase in the relative number of potential pathogenic bacteria in space.
The composition of intestinal, nasal and oral flora has been shown to change even during short spaceflights.
Changes in the diversity and number of gut microflora have been linked to a deficient immune system as well as immunological dysregulation.
To maintain astronaut health in orbit, an awareness of the importance of a balanced gut microbiome to maintaining immune homeostasis and resistance to infections is valuable.
Studies have shown that important immune parameters are decreased during spaceflight.
Reductions in the number and proportion of lymphocytes and their cytokine production, depression of dendritic cells function and T-cell activation, and finally reduction in numbers of monocytes and precursors of macrophages have been noted.
Upper respiratory problems, influenza, viral gastroenteritis, rhinitis, pharyngitis and mild dermatologic problems are among the common illnesses observed in astronauts.

Future Perspective: Considering Probiotics as a Countermeasure

On Earth, probiotics have been shown to improve both innate and adaptive immune responses.
An impaired digestive system might endanger the mission as well as the health of the astronaut.
One countermeasure to be considered would be replenishing the astronaut's intestinal microflora by introducing immune-enhancing probiotic bacteria periodically during the mission.
A series of experiments need to be launched to confirm the efficacy and safety of using probiotics in space.
There may be a future where astronauts utilize probiotics to counteract the potential effect of pathogenic bacteria during spaceflight.