New York, June 29 (IANS) Scientists at NASA organise regular checks to ensure that the International Space Station (ISS) has one of the cleanest living environments and is free from bacteria and other micro-organisms, the space agency said.

"Once every three months, we sample from two locations in each module of the US segment of the station," Mark Ott, a microbiologist at NASA's Johnson Space Center, said in a statement.

Samples collected from surfaces and from the air are cultured on plates containing a growth medium, one specific for bacteria and the other for fungi. Those plates return to the ground and scientists identify each organism that grows on them.

The study, published in the journal of Microbiome, identified 11 strains of bacterium belonging to what microbiologists call the Bacillus anthracis, cereus, thuringiensis group, or Bacillus cereus group.

While this large family of microbes includes some bad bugs, Bacillus is extremely common on the Earth and around humans, so finding this type of bacteria on the space station is not unusual, the scientists said.

Using DNA hybridisation, researchers identified individual species in the samples and, while some were a close match to Bacillus anthracis type strains, they did not have the physical characteristics or the toxin-producing plasmids required to consider them a potential risk.

Further, drinking water on the ISS is treated similarly to the water we drink on earth to kill and keep micro-organisms from growing with regular monitoring on the station's drinking water systems.

"The astronauts' drinking water is, microbiologically speaking, cleaner than just about anything they drink on earth," Ott said.

In addition, the medical staff keeps a particularly sharp eye out for micro-organisms that pose a risk to the health of astronauts and when any turn up, the space station gets a more-thorough-than-usual cleaning.

"We should be investigating new and different ways of monitoring spacecraft for micro-organisms but we must be careful when we interpret the results," Ott added.

Continued research is being done to understand what organisms grow on the space station and how they affect an astronaut's health, the scientists said.

--IANS

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