The occurrence of beta-glucuronidase activity, a main characteristic of Escherichia coli and the presence of the uid chromosomal region of E. coli, coding for this enzyme, were tested on representative members of enteric bacteria. DNA hybridization techniques using uid probes and amplification experiments of uidA gene by the polymerase chain reaction (PCR) confirmed the specificity of uid genes for E. coli and Shigella spp. (i.e., S. boydii, S. dysenteriae, S. flexneri and S. sonnei), independent of the beta-glucuronidase phenotype of bacterial strains. This specificity seemed to be conserved when studies were extended to a wide range of bacteria. It was not possible to distinguish E. coli from Shigella spp. The detection sensitivity using double stranded DNA radiolabeled probes was 3 x 10(4) bacteria and could be brought down to 8 bacteria by PCR. Thus, the uid genes appeared to be ideal candidates for DNA probes technology to detect E. coli-Shigella species.