If a rolling stone gathers no moss, a bacterium like S. typhimurium appears to gather virulence when its movement is slowed down and fluid shear across its surface is minimized. Nickerson speculates that Salmonella encounters just such conditions not only during spaceflight but also in vivo in an infected individual when the bacterium makes contact with an intestinal host cell and becomes ensnared in the fingerlike projections known as microvilli.
Thus, space travel may trick the microbes into behaving as though they were in an environment hospitable to cell infection, thereby switching on an increased virulence response, given appropriate environmental preconditions. "They're responding to an environmental signal that they're used to seeing right here on earth, during the natural course of the infectious disease process," Nickerson states, emphasizing that this response is masked in traditional microbial studies performed using lab cell cultures, which fail to replicate the low fluid shear conditions found in vivo, particularly in the gastrointestinal tractSalmonella's favored site of infection.
One result of spaceflight not replicated in the earthly bioreactor simulations was the formation of what appear to be biofilmsconglomerations of bacterial cells associated with infectious virulence. Nickerson emphasizes the potential importance, should such findings be confirmed. Up to 70 percent of bacterial infections in humans may be associated with the formation of such biofilms, which seem to arm bacterial pathogens with formidable resistance to the host's immune system as well as to antibiotics.
How do the disparate variablesextracellular phosphate concentration, mechanical forces like flui
|Contact: Joe Caspermeyer|
Arizona State University