A new study has shown that in situations imitating microgravity, as found in environments such as the International Space Station, microbes behave differently.
Researchers found that in conditions which simulate microgravity during spaceflight, the foodborne pathogen salmonella infects 3D models of human intestinal tissue at much higher levels.
The finding could be important for planning future long-range space missions, says Arizona State University (ASU) researcher Cheryl Nickerson.
This study builds on previous work by the same team showing that physical forces of fluid shear acting on both the pathogen and host can transform the way it works.
Fluid shear is a measurement of force within moving liquids.
Understanding this subtle interplay of host and pathogen during infection is critical to ensuring astronaut health, particularly on extended space missions.
Such research also sheds new light on the still largely mysterious processes of infection on Earth, as low fluid shear forces are also found in certain tissues in our bodies that pathogens infect, including the intestinal tract.
The 3D co-culture intestinal model used in this study more faithfully replicates the structure and behaviour of the same tissue within the human body and is more predictive of responses to infection, as compared with conventional laboratory cell cultures.
Results showed dramatic changes in gene expression of 3D intestinal cells.
Many of these changes occurred in genes known to be intimately involved with S. typhimurium's prodigious ability to invade and colonise host cells and escape surveillance and destruction by the host's immune system.
"A major challenge limiting human exploration of space is the lack of a comprehensive understanding of the impact of space travel on crew health," Nickerson says.
"This challenge will negatively impact both deep space exploration by professional astronauts, as well as civilians participating in the rapidly expanding commercial space market in low Earth orbit.
“Since microbes accompany humans wherever they travel and are essential for controlling the balance between health and disease, understanding the relationship between spaceflight, immune cell function, and microorganisms will be essential to understand infectious disease risk for humans."
Nickerson, who co-directed the new study with Jennifer Barrila, is a researcher in the Biodesign Center for Fundamental and Applied Microbiomics and is also a professor with ASU's School of Life Sciences. The research appears in the current issue of the journal Frontiers in Cellular and Infection Microbiology
For more than 20 years, Nickerson has been a pioneer in exploring the effects of the reduced microgravity environment of spaceflight on a range of pathogenic microbes and the impact on interactions with human cells and animals they infect.
Among their important findings is that the low fluid shear conditions associated with the reduced gravity environment of spaceflight and spaceflight analogue culture are similar to those encountered by pathogens inside the infected host, and that these conditions can induce unique changes in the ability of pathogenic microbes like Salmonella to aggressively infect host cells and exacerbate disease, a property known as virulence.
The infectious agent explored in the new study, S. typhimurium, is a bacterial pathogen responsible for gastrointestinal disease in humans and animals.
Salmonella is the leading cause of death from foodborne illness in the US.
Astronauts face a double risk from infectious disease during their missions far from earth. The combined rigours of spaceflight act to weaken their immune systems.
At the same time, some pathogens like salmonella may be triggered by low fluid shear conditions induced by microgravity to become more effective infectious agents.
With longer spaceflight missions in the advanced planning stages and the advent of civilian space travel rapidly emerging, safeguarding space travellers from infectious disease will be vital.
Studies like the current one are also helping to pull back the curtain on the infection process, revealing foundational details with broad relevance for the battle against diseases, on Earth and beyond.
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