Transfer of gentamicin resistance between cultures of Staphylococcus aureus in nutrient broth, serum and urine

Only one of 23 gentamicin-resistant cultures of Staphylococcus aureus transferred its resistance in mixed culture in broth to the non-lysogenic S. aureus strain 1030; the transfer-frequency was 10(-3)-10(-4). Transfer between non-lysogenic clones of strain 1030 occurred at a similar frequency in urine, and at a frequency of approximately 10(-1) in serum. The resistance determinant for transfer between non-lysogenic clones was usually linked to phage genome, as shown by the possession by resistant recipients of immunity to typing phage 75, plaque-forming particles in their culture filtrates and inducibility by mitomycin C. Stability of the resistance on storage and transduction kinetics suggested that these genes were chromosomal. Two resistant derivatives were isolated that had lost some phage functions and were unable to transfer their resistance further. The epidemiology of gentamicin resistance may in part be explicable by the transient formation of an auto-transmissible element with subsequent integration of the resistance genes into a variety of replicons (i.e., transposition).