EcAMSat spaceflight measurements of the role of σs in antibiotic resistance of stationary phase Escherichia coli in microgravity.

We report the results of the EcAMSat (Escherichia coli Antimicrobial Satellite) autonomous space flight experiment, investigating the role of σs in the development of antibiotic resistance in uropathogenic E. coli (UPEC) in microgravity (µ-g). The presence of σs, encoded by the rpoS gene, has been shown to increase antibiotic resistance in Earth gravity, but it was unknown if this effect occurs in µ-g. Two strains, wildtype (WT) UPEC and its isogenic ΔrpoS mutant, were grown to stationary phase aboard EcAMSat, an 11-kg small satellite, and in a parallel ground-based control experiment; cell growth rates for the two strains were found to be unaltered by µ-g. After starvation for over 24 h, stationary-phase cells were incubated with three doses of gentamicin (Gm), a common treatment for urinary tract infections (which have been reported in astronauts). Cellular metabolic activity was measured optically using the redox-based indicator alamarBlue (aB): both strains exhibited slower metabolism in µ-g, consistent with results from previous smallsat missions. The results also showed that µ-g did not enhance UPEC resistance to Gm; in fact, both strains were more susceptible to Gm in µ-g. It was also found, via a second ground-control experiment, that multi-week storage in the payload hardware stressed the cells, potentially obscuring small differential effects of the antibiotic between WT and mutant and/or between µ-g and ground. Overall, results showed that the ∆rpoS mutant was 34-37% less metabolically active than the WT for four different sets of conditions: ground without Gm, ground with Gm; µ-g without Gm, µ-g with Gm. We conclude therefore that the rpoS gene and its downstream products are important therapeutic targets for treating bacterial infections in space, much as they are on the ground.

Payload hardware and experimental protocol development to enable future testing of the effect of space microgravity on the resistance to gentamicin of uropathogenic Escherichia coli and its σs-deficient mutant.

Human immune response is compromised and bacteria can become more antibiotic resistant in space microgravity (MG). We report that under low-shear modeled microgravity (LSMMG), stationary-phase uropathogenic Escherichia coli (UPEC) become more resistant to gentamicin (Gm), and that this increase is dependent on the presence of σs (a transcription regulator encoded by the rpoS gene). UPEC causes urinary tract infections (UTIs), reported to afflict astronauts; Gm is a standard treatment, so these findings could impact astronaut health. Because LSMMG findings can differ from MG, we report preparations to examine UPEC's Gm sensitivity during spaceflight using the E. coli Anti-Microbial Satellite (EcAMSat) as a free-flying "nanosatellite" in low Earth orbit. Within EcAMSat's payload, a 48-microwell fluidic card contains and supports study of bacterial cultures at constant temperature; optical absorbance changes in cell suspensions are made at three wavelengths for each microwell and a fluid-delivery system provides growth medium and predefined Gm concentrations. Performance characterization is reported here for spaceflight prototypes of this payload system. Using conventional microtiter plates, we show that Alamar Blue (AB) absorbance changes can assess the Gm effect on E. coli viability, permitting telemetric transfer of the spaceflight data to Earth. Laboratory results using payload prototypes are consistent with wellplate and flask findings of differential sensitivity of UPEC and its ∆rpoS strain to Gm. if σs plays the same role in space MG as in LSMMG and Earth gravity, countermeasures discovered in recent Earth studies (aimed at weakening the UPEC antioxidant defense) to control UPEC infections would prove useful also in space flights. Further, EcAMSat results should clarify inconsistencies from previous space experiments on bacterial antibiotic sensitivity and other issues.