Variation in the properties of a strain of Staphylococcus aureus isolated over three months from a single hospital.

A strain of Staphylococcus aureus has been isolated from a hospital environment over 3 months. Every isolate was lysed by phage 77, had high-level resistance to streptomycin, and was resistant to about 250 pg per ml of both tetracycline and sulphonamide; a combination of sulphamethoxazole and trimethoprim produced little bacteristatic synergy towards each isolate. All These organisms were thus considered to be "the same"; the variation in other properties was probably due to rapid evolutionary change in vivo. the variation in senxitivity to methicillin and neomycin, and the absence of penicillinase production in some isolates, probably indicated loss of the relevant genes. Several isolates had probably acquired resistance to lincomycin by a one-step mutatuon in vivo. The usefulness of lincomycin and analogues in treating staphylococcal infections seems limited.