Investigations of the Occurrence of Gentamicin-Resistant Staphylococcus aureus

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Abstract
During the 19-month period from June 1976 to December 1977, 90 patients became colonized or infected with gentamicin-resistant Staphylococcus aureus (GRS). Of 63 adults, 56 had hospital-acquired GRS, whereas only 9 of 27 children had hospital-acquired GRS (P < 0.001). The other 7 adults and 18 children had GRS present on admission. More than half of those who acquired GRS in the hospital had received prior aminoglycoside therapy. Attack rates were higher in adults than in children and significantly higher on the plastic surgery service than on any other adult service. Phage typing revealed a single-strain outbreak on the plastic surgery ward involving 11 patients, whereas other isolates were of several phage types. Community-acquired GRS occurred more frequently in rural native communities (P < 0.02) and may be related to the use of topical gentamicin. Of 17 native children, 10 were from the same area but there was no common phage type. Agar dilution minimal inhibitory concentration (MIC) testing confirmed that all isolates were gentamicin resistant (MIC ≥ 8 μg/ml) and almost all were tobramycin resistant (MIC ≥ 8 μg/ml). Although the MIC distribution between gentamicin disk-susceptible and -resistant strains was significantly different, MIC's for 90% of gentamicin disk-resistant strains were ≤8 μg of amikacin per ml, and MIC's for 92% of the strains were ≤4 μg of netilmicin per ml.