Copresence of tet(K) and tet(M) in Livestock-Associated Methicillin-Resistant Staphylococcus aureusClonal Complex 398 Is Associated with Increased Fitness during Exposure to Sublethal Concentrations of Tetracycline

ABSTRACTThe tetracycline resistance gene tet(K) was shown to be integrated within the predominant staphylococcal cassette chromosome mec(SCCmec) element of Danish livestock-associated methicillin-resistant Staphylococcus aureusCC398 (LA-MRSA CC398). These LA-MRSA CC398 isolates already possessed tet(M), but the acquisition of tet(K) significantly improved their fitness at sublethal concentrations of tetracycline. Because tet(K) is genetically linked to SCCmec, the use of tetracycline in food animals may have contributed to the successful spread of LA-MRSA CC398.