Gentamicin-Resistant Staphylococci as Hospital Flora: Epidemiology and Resistance Plasmids

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Abstract
In 1979, gentamicin-resistant (Gm1) Staphylococcus aureus was recovered from the clinical specimens of 22 epidemiologically unrelated hospitalized patients; 78% of the patients evaluated were also colonized with Gm1 coagulase-negative staphylococci. Endonuclease fingerprinting was used to compare the Gm1 plasmids within pairs of isolates of S. aureus and coagulase-negative staphylococci recovered from nine patients. Plasmids differed between pairs but were concordant within four pairs. Thus, in vivo interspecific plasmid transfer, although infrequent, may be important in the sporadic occurrence of Gm1S. aureus. To define the epidemiology of endemic Gm1 coagulase-negative staphylococci, culture surveys were performed over two years. Gm1 coagulase-negative staphylococci were acquired by 80% of the infants in a special-care nursery that previously had an outbreak of Gm1S. aureus. Among adult inpatients, a 48% colonization rate was related to prior exposure to antibiotics. In contrast, no colonization was found in outpatients or antepartum mothers.