The susceptibility of five ruminal strains of Butyrivibrio fibrisolven
s to 23 antimicrobial compounds was examined to evaluate effects of an
timicrobials on this bacterium. All strains were very sensitive to ion
ophores and inhibitors of protein synthesis, except for aureomycin. On
the contrary, butyrivibrios were relatively insensitive to inhibitors
of carbohydrate metabolism and uncouplers. The strains studied displa
yed considerable variation in sensitivity to salinomycin, aureomycin a
nd bacitracin. The substrate used to support the bacterial growth (glu
cose or xylose) influenced the susceptibility of isolates to antimicro
bial agents. In one third of the measurements inhibitory concentration
s of antimicrobial compounds were lower with xylose-grown than with gl
ucose-grown cells. Different response of xylose-grown cultures to anti
microbials may reflect lower energy supply from fermentation of xylose
which was metabolized more slowly and with lower biosynthetic efficie
ncy.