Novel single-nucleotide variations associated with vancomycin resistance in vancomycin-intermediate Staphylococcus aureus Lee-Chung Lin,1 Shih-Cheng Chang,1,2 Mao-Cheng Ge,1 Tsui-Ping Liu,1 Jang-Jih Lu1–3 1Department of Laboratory Medicine, Chang Gung Memorial Hospital, Linkou, Taoyuan, Taiwan; 2Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan; 3Department of Medicine, College of Medicine, Chang Gung University, Taoyuan, Taiwan Abstract: Prolonged vancomycin usage may cause methicillin-resistant Staphylococcus aureus to become vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA). Mechanisms of vancomycin resistance of VISA and hVISA are still unclear. In this study, analyses of nucleotide sequence variations in 30 vancomycin-sensitive S. aureus (VSSA), 41 hVISA and 16 VISA isolates revealed 29 single-nucleotide variations in 12 genes (fmtC, graR, graS, htrA, mecA, pbp2, pbp4, srtA, tcaA, upps, vicK and vraR) that are related to cell wall synthesis or the two-component system. Six of these 29 single-nucleotide variations were novel and resulted in the following amino acid changes: Q692E in FmtC; T278I, P306L and I311T in HtrA; and I63V and K101E in Upps. Since P306L and I311T in HtrA and I63V in Upps were present in the majority (76.7%–86.7%) of VSSA isolates, these three amino acid variations may not be associated with vancomycin resistance. The other three amino acid variations (T278I in HtrA, K101E in Upps and Q692E in FmtC) were present in the majority (87.5%–93.8%) of hVISA and VISA isolates, but only in a small number (22.9%–25.7%) of VSSA isolates, suggesting that they are associated with vancomycin resistance. Keywords: MRSA, VSSA, hVISA, VISA