Estimation of growth rates of Escherichia coli BJ4 in streptomycin-treated and previously germfree mice by in situ rRNA hybridization.

The growth physiology of Escherichia coli during colonization of the intestinal tract was studied with four animal models: the streptomycin-treated mouse carrying a reduced microflora, the monoassociated mouse with no other microflora than the introduced strain, the conventionalized streptomycin-treated mouse, and the conventionalized monoassociated mouse harboring a full microflora. A 23S rRNA fluorescent oligonucleotide probe was used for hybridization to whole E. coli cells fixed directly after being taken from the animals, and the respective growth rates of E. coli BJ4 in the four animal models were estimated by correlating the cellular concentrations of ribosomes with the growth rate of the strain. The growth rates thus estimated from the ribosomal content of E. coli BJ4 in vivo did not differ in the streptomycin-treated and the monoassociated mice. After conventionalization there was a slight decrease of the bacterial growth rates in both animal models.

Ribosomal efficiency and growth rates of freshly isolated Escherichia coli strains originating from the gastrointestinal tract.

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.