The prevalence of sequences homologous to IS256 in clinical enterococcal isolates

Using dot blot hybridization techniques and an internal IS256 probe, we screened 103 clinical enterococcal isolates for the presence of sequences homologous to IS256. Most screened isolates exhibited resistance to one or more antimicrobial agents. Overall, hybridization to the internal IS256 probe was demonstrable in 88/103 (85%) isolates. 49/53 (92%) gentamicin-resistant isolates hybridized with the IS256 probe. In addition, 34/45 (76%) gentamicin-susceptible, aph2"(-) strains possessed sequences homologous to IS256. Southern hybridization experiments indicated that IS256 was frequently present in multiple copies in gentamicin-susceptible strains. These results suggest that IS256 is highly prevalent in clinical enterococcal isolates and that we may anticipate the emergence of novel, IS256-based composite mobile elements.