Oligonucleotide probe for the visualization of Escherichia coli/Escherichia fergusonii cells by in situ hybridization: specificity and potential applications.

There are several occasions when enumeration of Escherichia coli cells is needed. These include examination of urine specimens and water or food samples. Present methods rely on growth in more or less selective media (colony-forming units on agar or the most probable number method using liquid media). Unfortunately, no really selective medium with 100% efficiency of plating is available for E. coli. A 24-mer oligonucleotide probe (Colinsitu), complementary to a piece of 16S ribosomal ribonucleic acid, has been tested for specifically visualizing E. coli cells by in situ hybridization and epifluorescence microscopy. The fluorescent dye-labeled probe was able to stain cells of E. coli, Shigella spp. and E. fergusonii. Shigella spp. are known to belong to the E. coli genomospecies and E. fergusonii is the nomenspecies closest to E. coli by DNA-DNA hybridization. The probe did not stain any strain of 169 other genomospecies of the family Enterobacteriaceae or of a few other species frequently encountered in the environment. Revivification without cell division allowed the visualization of E. coli cells in contaminated water. In situ hybridization using the Colinsitu probe is a potential tool for the confirmation of (atypical) E. coli in reference centers and the rapid (3-6 h) detection and enumeration of E. coli in urine specimens, contaminated water and food. More work is needed to include in situ hybridization in laboratory routine.