Effect of simulated microgravity on the virulence properties of the opportunistic bacterial pathogen Staphylococcus aureus
- Paper number
IAC-06-A1.7.-A2.7.06
- Author
Prof. Peter W. Taylor, School of Pharmacy, University of London, United Kingdom
- Coauthor
Mrs. Helena Rosado, School of Pharmacy, University of London, United Kingdom
- Coauthor
Dr. Paul D. Stapleton, School of Pharmacy, University of London, United Kingdom
- Year
2006
- Abstract
Extended manned space flight will result in a diminution of immune status and cause profound changes in the human bacterial microbiota, leading to an increased risk of infection. Experiments designed to examine the effect of short-term flight on the ultrastructure and antibiotic susceptibility aboard Salyut 7, Challenger and Discovery demonstrated large increases in the thickness of the staphylococcal cell wall following in-flight growth, accompanied by marked increases in the resistance of these bacteria and of the Gram-negative bacterium Escherichia coli to antibiotics. Also of concern for the well being of flight crew is evidence that microgravity acts as an environmental signal for expression of enhanced bacterial virulence in Gram-negative pathogens; for example, Salmonella typhimurium grown under low-shear modelled microgravity (LSMMG) displayed enhanced virulence for mice and more readily colonised the liver and spleen. As yet, such studies have not been extended to include opportunistic Gram-positive bacteria frequently associated with the human microflora and likely to pose a risk of infection on extended missions. We examined the effect of simulated microgravity on the parameters of virulence in clinical isolates of the Gram-positive pathogen Staphylococcus aureus. Three methicillin-sensitive S. aureus (MSSA) strains were grown in a Synthecon High Aspect Ratio Vessel (HARV) under LSMMG with the vessel rotated about the horizontal axis and compared with cells grown in the HARV positioned to rotate about the vertical axis (NG). There were no significant differences in the growth rates of MSSA grown under LSMMG compared to NG. Scanning electron microscopy indicated only minor morphological differences: LSMMG cells were more uniform and possessed a smoother surface than their NG counterparts. Microgravity significantly reduced the secretion of hemolysins by all three strains: with one strain, a three-fold reduction in hemolysin in the growth medium was noted. The kinetics of secretion of the hemolysins of major importance for virulence, such as staphylococcal α-toxin, were examined in detail using SDS-polyacrylamide gel electrophoresis and immunoblotting with specific antibodies. Carotenoid pigments such as staphyloxanthin are associated with the capacity of staphylococci to cause abscesses and to avoid host immune defenses: LSMMG elicited large reductions in pigment production in all strains examined. We conclude that, in contrast to published data on Gram-negative bacterial pathogens, simulated microgravity reduces the expression of some of the key virulence determinants associated with S. aureus.
- Abstract document
- Manuscript document
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