Phage-mediated transfer of tetracycline resistance in Staphylococcus aureus isolated from cattle in Brazil

Tetracycline-resistant strains of Staphylococcus aureus isolated from cattle in Brazil, were used as prospective donors for the transfer of resistance to laboratory strains, using mixed-culture and filter-mating protocols. Three lysogenic donors transferred tetracycline resistance in both mixed culture and during filter mating. In contrast, when a non-lysogenic strain was used as prospective donor, transfer was not detected using either mating protocol. In order to evaluate the involvement of phage, successful transfer experiments were repeated with the addition of sodium citrate, which sequestered calcium ions. Mixed-culture and filter-mating protocols did not result in the transfer of resistance. These results support the notion that transfer of the resistance determinant under both sets of conditions described here involve the same bacteriophage-mediated mechanism. Although transfer of tetracycline resistance was detected, without any attempt to create specialized transduction agents or to extract phages, the co-transfer of additional resistance markers indicated that it could not be conventional transduction.