Mobilizable multidrug resistance plasmid identified in Staphylococcus xylosus isolated from fermented soybean food

We identified two Staphylococcus xylosus strains that were isolated from the same Korean fermented soybean food with different antibiotic resistance (AR) profiles. Strain 14BME10 showed multidrug resistance to erythromycin and tetracycline, whereas strain 14BME18 was resistant to tetracycline only. We sought to elucidate the genetic background of the AR in these strains. A comparative genomic analysis with three other antibiotic-sensitive S. xylosus strains revealed AR determinants located on two mobilizable plasmids in the isolates. The 73.7-kb plasmid p14BME10-1, encoding the ABC-F-type ribosomal protection protein gene msr(A) and the Mph(C) family macrolide 2'-phosphotransferase gene mph(C), might have contributed to erythromycin resistance. The 4.4-kb plasmid harboring the tetracycline efflux major facilitator superfamily (MFS) transporter gene tet(K) conferred tetracycline resistance and showed 100% DNA sequence identity with the prototype tetracycline resistance plasmid pT181, widely identified in staphylococci. We discovered that the MOBP relaxase gene cluster in p14BME10-1 consists of four genes and an oriT, which might be involved in plasmid mobilization and was also found in many staphylococcal plasmids. The plasmid p14BME10-1 harbors multiple genes for replication, mobilization, transposition, recombination, and resistance to erythromycin, streptomycin, and bacitracin, indicating several occurrences of recombination and integration events but lacks the genes necessary for conjugal transfer.