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Title
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**Mycobacterium tuberculosis** strains with highly discordant rifampin susceptibility test results
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Author
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Abstract
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| The objectives of this study were to investigate the origin of highly discordant rifampin (rifampicin) (RMP) drug susceptibility test results obtained for Mycobacterium tuberculosis strains during proficiency testing. Nine Supra-National Tuberculosis Reference Laboratories tested the RMP susceptibilities of 19 selected M. tuberculosis strains, using standard culture-based methods. The strains were classified as definitely resistant (R) (n = 6) or susceptible (S) (n = 2) or probably resistant (PR) (n = 8) or susceptible (PS) (n = 3) based on rpoB mutations and treatment outcome. All methods yielded a susceptible result for the two S and three PS strains lacking an rpoB mutation and a resistant result for one R strain with a Ser531Leu mutation and one PR strain with a double mutation. Although the remaining 12 R and PR strains had rpoB mutations (four Asp516Tyr, three Leu511Pro, two Leu533Pro, one each His526Leu/Ser, and one Ile572Phe), they were all susceptible by the radiometric Bactec 460TB or Bactec 960 MGIT methods. In contrast, only one was susceptible by the proportion method on Löwenstein-Jensen medium and two on Middlebrook 7H10 agar. Low-level but probably clinically relevant RMP resistance linked to specific rpoB mutations is easily missed by standard growth-based methods, particularly the automated broth-based systems. Further studies are required to confirm these findings, to determine the frequency of these low-level-resistant isolates, and to identify technical improvements that may identify such strains. |
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Language
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English
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Source (journal)
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Journal of clinical microbiology. - Washington, D.C.
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Publication
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Washington, D.C.
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2009
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ISSN
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0095-1137
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DOI
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10.1128/JCM.01209-09
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Volume/pages
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47
:11
(2009)
, p. 3501-3506
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ISI
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000271373000018
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Full text (Publisher's DOI)
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Full text (publisher's version - intranet only)
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