FIG. 3.

Segregational stabilities of pSK1, pSK41, and derivatives in S. aureus strain RN4220. The values indicate the proportion of cells in a population, cultured in the absence of plasmid selection for the indicated number of generations, subsequently able to grow when plated on medium containing selection for the plasmid. Open and solid shapes distinguish data for each of two independent experiments. (A) Values for pSK1, pSK4829, and pSK4833, tested in S. aureus strain RN4220, are denoted by squares, diamonds and circles, respectively. The presence of pSK1 was indicated by growth in the presence of 100 μg of trimethoprim/ml, whereas retention of pSK4829 or pSK4833 was indicated by growth in the presence of 20 μg of erythromycin/ml. (B) Values for pSK41 and pSK5413, tested in S. aureus strains SK982 and RN4220, respectively, are denoted by squares and triangles, respectively. The presence of pSK41 was indicated by growth in the presence of 20 μg of gentamicin/ml, whereas retention of pSK5413 was indicated by growth in the presence of 10 μg of tetracycline/ml.