1. Multiply resistant strains of Staphylococcus aureus often harbor one or more extrachromosomal drug resistant factors as well as temperate prophages capable of mediating generalized transduction.
2. Spontaneous transduction occurs in mixed cultures of such staphylococcal strains, and the extrachromosomal resistance factors are involved more frequently than are chromosomal genes.
3. Spontaneous transduction of extrachromosomal determinants of erythromycin resistance and of linked penicillin-erythromycin resistance occurs in the kidneys of mice in which mixed infection has been induced.