BEHAVIOR OF BACTERIA AND ANTIBIOTICS UNDER SPACE CONDITIONS

We have previously reported an increase of the ''resistance'' to antib iotics of bacteria during space missions. In the present experiment, w e studied the growth of Escherichia coli cultured in vitro in space in the presence of dihydrostreptomycin: tritiated and nontritiated. This experiment was carried out during the STS 42 mission aboard the U.S. Space Shuttle Discovery (IML-1 program). Cells were cultured in plasti c bags and growth was stopped at six different time points by lowering the temperature to 5-degrees-C. Several methods were used: viable cel l counting by Colony Forming Units; total cell number by optical densi tometry; electron microscopy; radioactivity measurements. The investig ations show no difference between flight and ground experiments for th e cultures without antibiotic. The growth rate with antibiotic was acc elerated in flight, the growth yield was not changed, and there were n o differences in the ultrastructures. The results suggest some changes in antibiotic binding in space. We did not observe any differences be tween the cultures developed in flight in the 1-g centrifuge and the c ultures placed in the static rack in microgravity.