Genetic variation of streptomycin resistance in clinical strains of Staphylococcus aureus.

Abstract

Summary Of 74 distinct strains of Staphylococcus aureus obtained from clinical sources, about 70 per cent. were resistant to high levels of streptomycin (MIC>1 mg per ml) and 30 per cent. resistant to lower levels (MIC about 100 μg per ml). Streptomycin resistance in four strains exhibiting high-level resistance was stable on storage, whilst that in four strains with low-level resistance was unstable. Three of the latter were also resistant to other antibiotics; these resistances were also unstable, and in one of these strains (FAR4) there was evidence that streptomycin resistance was linked to erythromycin and neomycin resistance and to production of δ-haemolysin. Strain 649 is resistant only to streptomycin (low-level resistance); plasmid DNA with a molecular weight of about 38 million daltons corresponding to this resistance was isolated from this strain. Attempts to correlate the CCC-DNA from the multi-resistant strain FAR4 with its resistances were unsuccessful. Resistance to spectinomycin was not associated with resistance to streptomycin, but with erythromycin resistance or with neomycin resistance.