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

The growth physiologv of Escherichia coli during colonization of the intest inal tract was studied with four animal models: the streptomycin-treated mo use carrying a reduced microflora, the monoassociated mouse with no other m icroflora than the introduced strain, the conventionalized streptomycin-tre ated mouse, and the conventionalized monoassociated mouse harboring a full microflora. A 23S rRNA fluorescent oligonucleotide probe was used for hybri dization to whole E. coli cells fixed directly after being taken from the a nimals, and the respective growth rates of E. coli BJ4 in the four animal m odels were estimated by correlating the cellular concentrations of ribosome s with the growth rate of the strain. The growth rates thus estimated from the ribosomal content off. coli BJ4 in vivo did not differ in the streptomy cin-treated and the monoassociated mice. After conventionalization there wa s a slight decrease of the bacterial growth rates in both animal models.