global effect of rpob mutation on protein expression in enterococcus faecium

background enterococcus faecium is an important nosocomial pathogen and has developed resistance to multiple antibiotics, such as vancomycin. nitrofurantoin is active against e. faecium and e. faecalis, including vana- and vanb-positive isolates. objectives to investigate the role of rpob mutation in e. faecium. methods the growth rate and reactive oxygen species (ros) levels were determined. the proteomic profiles of e. faecium b42 and its rifr mutant b42-r7 were also compared. complement experiments were performed to elucidate the role of nitroreductase in nitrofurantoin resistance. results the rifr mutant (b42-r7, rpob h489d) of e. faecium had a lower growth rate and higher ros levels. overexpression of nitroreductase in e. faecium b42-r7 was observed in proteomic analyses. enhanced expression of nitroreductase in escherichia coli increased the sensitivity to nitrofurantoin. conclusions the rpob mutation in e. faecium not only altered the susceptibility to rifampin, but also affected global protein expression, including nitroreductase. nitroreductase expression in e. faecium b42-r7 might play a role in nitrofurantoin resistance.