Vancomycin resistant Enterococcus (E.) faecium (VRE) is a healthcare-associated pathogen causing severe diseases in immunocompromised patients. The dysregulation of immune functions in astronauts during spaceflight, as previously shown, elevates the risk of infections from both endogenous and exogenous pathogens. Compounding this concern, treatment options are restricted during long-term missions. Consequently, we seek to understand how opportunistic gastrointestinal bacteria, such as E. faecium, may alter their antimicrobial susceptibility, desiccation tolerance, and biofilm formation in response to the absence of gravity. Understanding these dynamics has implications for healthcare on Earth and in space.

We tested the changes in antibiotic susceptibility of Vancomycin susceptible (VSE), Vancomycin resistant (VRE) and Vancomycin-variable (VVE-B) E. faecium isolates to 22 different antibiotics, after 7 days of incubation in simulated microgravity (sim. µg) and at normal gravity (1 g). All isolates were also characterized regarding their biofilm formation and tolerance to desiccation after sim. µg. We observed in- and decrease in MIC (Minimum Inhibitory Concentration) for seven isolates to Ceftarolin, Gentamycin, Moxifloxacin, Oxacillin, Rifampicin, Synercid and Vancomycin after sim. µg. Moreover, 55 % (23/42 isolates) showed an increase in biofilm formation and 59 % (25/42) increase in desiccation tolerance after sim. µg.

This study provides first insights on how E. faecium adapts its resistance behavior under spaceflight analog conditions like sim. µg. The found alterations distinctly demonstrate the adaptability of E. faecium while also showing a great variability to sim. µg. To prevent VRE infections and guarantee health of the crewmembers for future long-term space missions, it is essential to improve the understanding about the tenacity of VRE and gain knowledge about the influence of microgravity on the resistance behavior to different stressors. Understanding these dynamics has implications for healthcare on Earth and in space.