Characterization of rifampin-resistant Staphylococcus aureus nasal carriage in patients receiving rifampin-containing regimens for tuberculosis Yu-Tsung Huang,1–3 Chun-Hsing Liao,1,4 Shey-Ying Chen,5 Chia-Jui Yang,1,4 Hsin-Sui Hsu,1 Lee-Jene Teng,2,3 Po-Ren Hsueh2,6 1Department of Internal Medicine, Far Eastern Memorial Hospital, New Taipei City, Taiwan; 2Department of Laboratory Medicine, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei, Taiwan; 3Department of Clinical Laboratory Science and Medical Biotechnology College of Medicine, National Taiwan University, Taipei, Taiwan; 4Department of Internal Medicine, College of Medicine, Yang-Ming University, Taipei, Taiwan; 5Department of Emergency Medicine, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei, Taiwan; 6Department of Internal Medicine, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei, Taiwan Objectives: This study investigated molecular characteristics of rifampin (RIF)-resistant (RIF-R) Staphylococcus aureus isolates recovered from patients receiving RIF-containing regimens for tuberculosis (TB). Patients and methods: Patients with TB who received RIF-containing regimens from November 2009 to May 2011 at a medical center were enrolled. Nasal swabs for S. aureus culture were obtained at the time of enrollment, and then every two months until two months after RIF treatment had been completed. Genetic relatedness of the isolates was determined using pulsed-field gel electrophoresis, multilocus sequence typing, and gene typing of spa and SCCmec. The presence of RIF resistance-associated mutations in rpoB, and fusidic acid resistance genes fusB and fusC in the S. aureus isolates were analyzed. Results: Among the 200 patients enrolled in this study, 152 completed follow-ups during treatment, and 114 completed two months of follow-up after discontinuing use of RIF. At enrollment, ten patients (5%) had nasal colonization with S. aureus, namely eight with methicillin-susceptible S. aureus (MSSA), and two with methicillin-resistant S. aureus (MRSA, ST59-SCCmecIV-RIF-susceptible). All these patients were decolonized after RIF usage. Two patients with MSSA colonization at enrollment showed recolonization with genetically unrelated MSSA strains two months after completion of RIF treatment. There were five ST45-SCCmecVT-RIF-R strains from two patients isolated during RIF exposure. Sequencing of rpoB in the RIF-R S. aureus isolates revealed different mutation sites between the MSSA and MRSA isolates. Conclusion: RIF-R S. aureus strains are more likely to result in persistent nasal carriage in TB patients receiving RIF treatment. Monitoring of emergence and possible dissemination of the MRSA ST45 strains among TB patients treated with RIF in Taiwan is warranted. Keywords: Staphylococcus aureus, methicillin-resistant S. aureus, rifampin resistance, tuberculosis, nasal carriage, Taiwan