Identification offusB-Mediated Fusidic Acid Resistance Islands in Staphylococcus epidermidis Isolates

Abstract

ABSTRACTTo understand the high prevalence offusBgenes in fusidic acid-resistantStaphylococcus epidermidis, analysis of resistance elements in 34 isolates was performed. First, sequence analysis of theaj1-LP-fusBregion indicated that at least three types were present. Type I contained full-lengthaj1, type II contained a partialaj1truncated from nucleotide position 93 to 421, and type III contained a more truncatedaj1that retained only the last 37 bp. Isolates with type I or type IIaj1displayed slightly higher levels of resistance to fusidic acid (MICs, 8 to 32 μg/ml) than did those with type IIIaj1(MICs, 4 to 16 μg/ml). Subsequent sequencing of the flanking regions offusBfrom four selected isolates carrying different types ofaj1-LP-fusBregions revealed that thefusBgenes were all located on phage-related resistance islands (RIs), referred to as SeRIfusB-2793, SeRIfusB-704, SeRIfusB-5907, and SeRIfusB-7778, respectively. Among them, three islands (SeRIfusB-2793, SeRIfusB-704, and SeRIfusB-5907) were located downstream ofgroEL(corresponding to the 44-min position based onStaphylococcus aureuswhole genomic sequences), and one (SeRIfusB-7778) was located downstream ofrpsR(corresponding to the 8-min position). All of the RIs were inserted into integrase-recognizedattsites. Among 34 isolates, the insertion sites offusBRIs were mostly (28/34, 82%) located downstream ofgroELand two were located downstream ofrpsR, but four remained unidentified. The pulsotype distribution indicated thatfusB-containingS. epidermidisisolates were heterogeneous. In conclusion, thefusBresistance determinant inS. epidermidiswas highly associated with phage-related RIs. This is the first report offusBRI inS. epidermidis.