In vitro evaluation of rosaramicin with special reference to the risk of resistance

Abstract

The macrolide antibiotic rosaramicin was compared in vitro with erythromycin. Rosaramicin had an intrinsic potency greater than erythromycin against Haemophilus spp., Bacteroides spp. and Campylobacter. Rosaramicin was bactericidal against Staph. aureus when the pH was > 7 0. The rate of bacterial killing of Staph. aureus 1030 was increased by the possession of several plasmids. Cultures of Staph. aureus examined for macrolide resistance were only resistant to rosaramicin as part of a constitutive resistance to all macrolide antibiotics and lincomycins. During clinical use of rosaramicin, staphylococci will be expected only to mutate to resistance to this antibiotic if they are already inducibly resistant to erythromycin. Rosaramicin resistant cultures of Staphylococcus aureus grew more slowly in the presence of 2 0 mg rosaramicin/l than in antibiotic free medium.