[65]

RESISTANCE TO PSEUDOMONAS AERUGINOSA IS DECREASED IN HINDLIMB UNLOADED MICE.  H.O. Aviles, T. Belay, K. Fountain, M. Vance, and G. Sonnenfeld.  Dept. of Microbiology, Biochemistry, & Immunology, Morehouse School of Medicine, Atlanta, GA.

   In humans and laboratory animals, immune function is modulated during and after exposure to space flight conditions.  However, it is not clear whether space flight induced immunomodulation results in altered resistance to infection.  Ground-based models have proven to be very useful for study of this problem.  The hindlimb unloading rodent has been extensively used for creating conditions similar to those that occur during space flight.  The objective of this study was to asses the effect of hindlimb unloading on resistance to Pseudomonas aeruginosa.  P. aeruginosa, an increasingly prevalent opportunistic human pathogen, is one of the most common gram-negative bacterium found in nosocomial infections and has great potential to colonize immunocompromised hosts.  It has also been isolated from infections in astronauts.  Hindlimb unloaded and control (restrained and normally housed) mice were subcutaneously infected with a dose of P. aeruginosa lethal for 50% (LD₅₀) of normally housed mice.  Survival was significantly decreased in the hindlimb unloaded group compared to controls (p=0.009).  The mean day of death was also decreased in the hindlimb unloaded group (4.7±0.8) compared to the control group (8.9±0.9) (p<0.01).  The results of this study suggest that hindlimb unloading enhanced dissemination leading to decreased survival.  The mechanism of induction of altered resistance are not yet completely defined.   However, the production of critical cytokines involved in the control of bacterial growth, such as tumor necrosis factor-a, may be impaired.  The National Aeronautics and Space Administration supported this study under NASA cooperative agreement NCC 9-58 with the National Space Biomedical Research Institute.

[