Impact of space flight on bacterial virulence and antibiotic susceptibility Peter William Taylor School of Pharmacy, University College London, London, UK Abstract: Manned space flight induces a reduction in immune competence among crew and is likely to cause deleterious changes to the composition of the gastrointestinal, nasal, and respiratory bacterial flora, leading to an increased risk of infection. The space flight environment may also affect the susceptibility of microorganisms within the spacecraft to antibiotics, key components of flown medical kits, and may modify the virulence characteristics of bacteria and other microorganisms that contaminate the fabric of the International Space Station and other flight platforms. This review will consider the impact of true and simulated microgravity and other characteristics of the space flight environment on bacterial cell behavior in relation to the potential for serious infections that may appear during missions to astronomical objects beyond low Earth orbit. Keywords: Staphylococcus aureus, International Space Station, microgravity, bacterial phenotypes, low-shear modeled microgravity, spacecraft contamination