Abstract
A single plasmid clone was predominantly responsible for gentamicin resistance at the Minneapolis Veterans Administration Medical Center (MVAMC) for 9 years, although two unrelated R plasmids were found. Epidemiological data and restriction endonuclease analysis of 25 plasmid isolates suggested that the clonally derived plasmid population had persisted at the hospital. However, one case of reintroduction of the original epidemic plasmid from a hospital in another state was documented 4 years after the introduction of the original plasmid to the MVAMC. Resistance by the clonally derived plasmid population was not localized geographically within the MVAMC but rather was a hospital-wide problem. Furthermore, previously described classes of DNA rearrangement of the original plasmid were also widely disseminated in the hospital, implying that spread of strains bearing index-related plasmids was relatively unimpeded within the MVAMC despite extensive barrier isolation and cohorting measures. Potential environmental reservoirs of the plasmids were identified in hospital sinks and drains, but their relation to continued patient infection is not known.