It has been previously reported that for natural Escherichia coli isolates from the ECOR collection, there were differences in the ribosomal efficiencies and there was a direct correlation between growth rate and the ribosome efficiency (R-factor). The aim of this study was to determine whether strains freshly isolated (i.e. subcultured < 5 times) from the gastrointestinal tract ecosystem also exhibited this correlation. Eleven E. coli and two Enterobacter spp. isolates from either humans, pigs, rats or a mammoth were investigated. Considerable variability in the R-factor was noted using an in vitro translation assay, however no consistent correlation between the R-factor and growth rate was noted.