Development of erythromycin-resistance in Staphylococcus aureus as a consequence of high erythromycin consumption

In a mixed ward for skin and venereology patients the erythromycin consumption was 6-8 fold higher than in other wards at the same hospital. Erythromycin-resistance occurred in 15.5% of the infecting Staphylococcus aureus strains isolated from this ward, compared with 3.5% in other wards of the hospital and 2.3% in Denmark as a whole. The resistant strains belonged to different phage-type patterns, but 18 out of 19 strains contained a 1.5 MDa plasmid and had an erythromycin-inducible resistance mechanism. Erythromycin resistance was frequent (approximately 10%) among Danish S. aureus strains in the years 1963 to 1969, mainly due to the spread of multiply-resistant strains of the 83A complex. During the last ten years, however, only 1-2% of the strains have been resistant, but a slow increase in resistance has taken place during the last three years among strains of all phage patterns including strains of group II, the 94, 96 complex and type 95.