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Is the real barrier between humans and extended space flight a biological one? September 23, 2006

Posted by Hegemony in Health, Science.
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There are many factors making human space flight a complicated endeavor. Now, there seems to be yet another problem to be dealt with. Research indicates that many pathogenic organisms become more virulent in a microgravity environment. They can replicate faster and show increased antibiotic resistance. If long term space flights are to be a reality this problem must be solved. This phenomenon may also help us understand the mechanisms of bacterial resistance and allow the advent of new treatments.

Though it is unclear if astronauts experience immunosuppression there are many possible causative factors. For instance radiation, weightlessness, altered nutrition, and co-existence in an isolated confined environment (ICE). This is only part of the danger. Low gravity environments also seem to be conducive to the growth of the bacteria themselves. Studies in both space and simulated microgravity environments indicate that bacteria can develop increased stress resistance and virulence. These terrestrial experiments are needed because there are so few opportunities to experiment in space itself. There are also several other factors that relate to the problem of microbes in space. These include the absence of hydrostatic load, reduced shelf-life of drugs, and micro-flora exchange among crew members.

Studies done on bacteria grown in space show that they often have decreased lag phase and thus a higher final cell population. Several decades of research also indicate that they develop antibiotic resistance while in the low gravity environment. These resistant traits are not retained upon return to Earth. The mechanism for this is currently unknown but much attention is focused on it.

A study done on five cosmonauts indicated that they had exchanged intestinal microflora during their mission. These organisms accumulate antibiotic resistant properties from the normal flora of the digestive tract. Similar results were obtained from the Apollo and space shuttle missions. Opportunistic pathogens have been found on both the ISS and Mir. This proves that the possibility of infection due to the exchange of microflora and immunosuppression is a real one.

Several studies done on bacteria in simulated micro-gravity illustrate some interesting points. Salmonella enterica grown in a micro-gravity environment showed both decreased necessary dose and time to death in mice. These bacteria were also resistant to acid, thermal, and osmotic stress. This allows them to survive longer periods of time in macrophages. Several studies are currently being done on this phenomenon, one of the on the ISS.

A series of terrestrial experiments using hind limb unloaded mice has produced expected results. The experimental mice showed decreased survival rates as well as decreased survival times. Another mouse experiment involved bacteria taken from three men living together in isolation for a year. The pathogenic organisms taken from them after this period showed increased virulence when injected into mice.

The hope is that the study of these properties of bacteria will give us critical insights into the development of antibiotic resistance in addition to allowing prolonged space flight. If new methods of controlling the emergence of resistant strains were found it would be a boon to humanity. Resistant organisms usually appear a few years after the introduction of a new antibiotic. Our current drugs are becoming obsolete. Since 1981 the rate of death from infectious disease has gone from 36 to 63 per 100,000 each year. Government funding has just recently begun coming back to antibiotic research. Originally, it was assumed that antibiotics would put an end to disease. Now the race is on to find new drugs.

By finding the solution to the space flight problem we may find new ways to combat microorganisms everywhere. With our current drugs loosing their effectiveness and many pharmaceutical companies spending their time on non-invasive disease the outlook is troubling. It is important that we work towards finding new methods of controlling microorganisms before the current generation of drugs become useless.

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