Acquired Antibiotic Resistance in Klebsiella pneumoniae Exposed to Short-Term Simulated Microgravity and Background Antibiotic Exposure

Space flight missions last for a long time so bacterial infection during missions is considered a potential risk for astronauts. Studies of bacterial antibiotic resistance under spaceflight and simulated microgravity (SMG) have shown lots of results. To better understand the antibiotic resistance of Klebsiella pneumoniae in the microgravity environment, an original K. pneumoniae original strain was cultured under SMG conditions combined with background antibiotic exposure (SMGA) as the experimental strain, while the control strain was cultured in a normal gravity environment without antibiotic exposure. At the beginning of the treatment, the growth curves of the experimental and control strains were drawn. After 20 cycles of incubation, the antibiotic susceptibility, genomic, transcriptomic, and proteomic tests were conducted on the experimental and control strains. After the treatment, the experimental and control strain was inoculated into shake flasks under normal gravity without antibiotic exposure as an eraser experiment. During and after 10 cycles of incubation in shake flasks, antibiotic susceptibility tests were repeatedly conducted. The results showed that SMG conditions still increased the growth rate of K. pneumoniae despite of the background antibiotic exposure. Sustained exposure to SMGA condition resulted in acquired antibiotic resistance, which persisted for a period even though the SMGA condition was removed. The mechanisms of acquired antibiotic resistance under SMGA condition might include the loss of porin OmpK35, overexpression of the efflux pump OqxAB and upregulation of the AcrAB-TolC multidrug efflux system.