Restriction fragment length polymorphism (RFLP) patterns and sequence analysis of high-level mupirocin-resistant meticillin-resistant staphylococci

High-level mupirocin resistance results from the acquisition of a mupirocin resistance (Mupr) plasmid carrying the mupA gene. In this study, we investigated the heterogeneous location of the mupA gene as well as sequence variations in mupA restriction fragment length polymorphism (RFLP) types of high-level mupirocin-resistant (MuH) staphylococci isolated from tertiary hospitals and long-term care facilities in South Korea. RFLP patterns of the mupA gene were investigated in 14 MuH staphylococci isolates, and sequence variations of the cassette-like construction composed of the transfer gene complex (trs), an insertion sequence (IS257-like) and the mupA gene of the Mupr plasmid were also studied. Among the 14 isolates, four different EcoRI/HindIII banding patterns were observed, which were determined to be caused by sequence deletion between the mupA gene and trsLM of the trs gene complex. Four different sequence types were also identified for the trsLM–IS257-like–mupA cassette. The IS257-like sequence of all MuH staphylococci showed two base pair substitutions and one base deletion compared with the sequence of IS257. The heterogeneous location of the mupA gene was caused by sequence deletion adjacent to the IS257-like sequence of the trsLM–IS257-like–mupA cassette construction, and the IS257-like sequence was found in all MuH staphylococci.