Ampicillin-resistant Enterococcus raffinosus in an acute-care hospital: case-control study and antimicrobial susceptibilities

A prospective study identified 9 (32%) of 28 ampicillin-resistant (MIC greater than or equal to 16 micrograms/ml) enterococcus isolates as Enterococcus raffinosus. A case-control study found no significant differences with respect to underlying diseases, catheterization, or surgery between patients with ampicillin-resistant E. raffinosus and those with ampicillin-susceptible Enterococcus spp. Prior treatment with antibiotics and prolonged hospitalization were more frequent among patients with ampicillin-resistant E. raffinosus. Patients with the same strain (determined by plasmid analysis) were frequently hospitalized concurrently.