High-Frequency Transfer Of Neomycin Resistance Between Naturally Occurring Strains Of Staphylococcus Aureus

SUMMARY A naturally occurring neomycin-resistant strain of Staphylococcus aureus was found to donate its resistance, together with cross-resistance to kanamycin and paromomycin, to a variety of sensitive staphylococci. The transfer occurred spontaneously and at relatively high frequency both in broth cultures and experimentally on the skin surface of volunteers. The mechanism of the transfer was transduction, which is believed to be mediated by an element composed of a defective prophage of serological group B and a determinant for neomycin resistance. The latter is probably located on a plasmid in the resistant cell, since strains harbouring the element tended to lose their resistance spontaneously, particularly at high temperatures. The effect of UV light on the transduction of the element was also characteristic of known plasmids. The phage-typing patterns of staphylococci able to acquire the neomycin-resistance marker in vitro were limited but similar to those of naturally occurring resistant strains. Since neomycin resistance of the type found naturally could not be established in the laboratory, it is probable that the acquisition of neomycin resistance may have occurred in vivo by high-frequency transduction.