Spaceflights results in the reduction of immune status of human beings and increase in the virulence of microorganisms, especially gram negative bacteria. The growth of Klebsiella pneumoniae is enhanced by catecholamines and during spaceflight, elevation in the levels of cortisols occurs. So it is necessary to know the changes in physiology, virulence, antibiotic resistance and gene expression of K. pneumoniae under microgravity conditions. The present study was undertaken to study effect of simulated microgravity on growth, morphology, antibiotic resistance and cross stress resistance of K. pneumoniae to various stresses. The susceptibility of simulated microgravity grown K. pneumoniae to ampicillin, penicillin, streptomycin, kanamycin, hygromycin and rifampicin were evaluated. The growth of bacteria was found to be fast compared with normal gravity grown bacteria and no significant changes in the antibiotic resistance were found. The bacteria cultured under microgravity conferred cross stress resistance to acid, temperature and osmotic stress higher than the normal gravity cultured bacteria but the vice versa was found in case of oxidative stress.

Abstract
 1. Introduction
 2. Materials and methods
  2.1. Bacterial strain and growth conditions
  2.2. Growth kinetics
  2.3. TEM and SEM analysis
  2.4. Acid stress survival test
  2.5. Thermal stress survival test
  2.6. Osmotic stress survival test
  2.7. Oxidative stress survival test
  2.8. Antibiotic susceptibility test
 3. Results
  3.1. Effect of microgravity on the growth of K. pneumoniae
  3.2. Morphological analysis
  3.3. Acid stress analysis
  3.4. Thermal stress analysis
  3.5. Osmotic stress analysis
  3.6. Oxidative stress analysis
  3.7. Antibiotic susceptibility test
 4. Discussion
 5. Conclusion
 References

• Duraisamy Kalpana(Department of Forest Science and Technology, Institute of Agricultural Science and Technology, Chonbuk National University)
• Hyo-Jung Cha(Department of Forest Science and Technology, Institute of Agricultural Science and Technology, Chonbuk National University)
• Moon-Ki Park(Department of Herbal Pharmaceutical Eng., DeaguHaany University)
• Yang-Soo Lee(Department of Forest Science and Technology, Institute of Agricultural Science and Technology, Chonbuk National University) Corresponding author