title: Ribosomal and non-ribosomal resistance to oxazolidinones: species-specific idiosyncrasy of ribosomal alterations.
abstract: A derivative of Mycobacterium smegmatis, which carries only one functional rRNA (rrn) operon, was used to isolate mutants resistant to the ribosome-targeted antibiotic linezolid. Isolation and characterization of linezolid-resistant clones revealed two classes of mutants. Ribosomes from class I mutants are resistant to oxazolidinones in an in vitro peptidyl transferase assay, indicating that resistance maps to the ribosome component. In contrast, ribosomes from class II mutants show wild-type susceptibility to a linezolid derivative in vitro, pointing to a non-ribosomal mechanism of resistance. Introduction of a wild-type ribosomal RNA operon into linezolid-resistant strains restored linezolid sensitivity in class I mutants, indicating that resistance (i) maps to the rRNA and (ii) is recessive. Sequencing of the entire rrn operon identified a single nucleotide alteration in 23S rRNA of class I mutant strains, 2447G --> T (Escherichia coli numbering). Introduction of mutant rrl2447T into M. smegmatis rrn- resulted in a linezolid-resistant phenotype, demonstrating a cause-effect relationship of the 2447G --> T alteration. The 2447G --> T mutation, which renders M. smegmatis linezolid resistant, confers lethality in E. coli. This finding is strong evidence of structural and pos-sibly functional differences between the ribosomes of Gram-positive and Gram-negative bacteria. In agreement with the results of the in vitro assay, class II mutants show a wild-type sequence of the complete rRNA operon. The lack of cross-resistance of the class II mutants to other antibiotics suggests a resistance mechanism other than activation of a broad-spectrum multidrug transporter.
authors.affiliation: Institut für Medizinische Mikrobiologie, Universität Zürich, Gloriastr. 30/32, CH-8028 Zürich, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Sander
authors.forename: L
authors.initials: L
authors.lastname: Belova
authors.forename: Y G
authors.initials: YG
authors.lastname: Kidan
authors.forename: P
authors.initials: P
authors.lastname: Pfister
authors.forename: A S
authors.initials: AS
authors.lastname: Mankin
authors.forename: E C
authors.initials: EC
authors.lastname: Böttger
mesh_terms: D000081:Acetamides / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001483:Base Sequence; D024881:Drug Resistance, Bacterial; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D000069349:Linezolid; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D020102:Mycobacterium smegmatis / Q000187:drug effects* / Q000235:genetics; D023303:Oxazolidinones / Q000494:pharmacology*; D012329:RNA, Bacterial / Q000737:chemistry / Q000187:drug effects / Q000235:genetics; D012338:RNA, Ribosomal, 23S / Q000737:chemistry / Q000187:drug effects / Q000235:genetics; D012270:Ribosomes / Q000187:drug effects*; D013045:Species Specificity; D012407:rRNA Operon / Q000187:drug effects / Q000235:genetics
chemical_list: D000081:Acetamides; D000900:Anti-Bacterial Agents; D023303:Oxazolidinones; D012329:RNA, Bacterial; D012338:RNA, Ribosomal, 23S; D000069349:Linezolid