title: Comparison of clinical isolates and in vitro selected mutants reveals that tlyA is not a sensitive genetic marker for capreomycin resistance in Mycobacterium tuberculosis.
abstract: OBJECTIVE
  The aim of this study was to clarify the conflicting data regarding cross-resistance and drug-resistance mechanisms for the cyclic peptide capreomycin and the aminoglycosides amikacin and kanamycin by comparing genotypes and phenotypes of clinical isolates and in vitro selected mutants of Mycobacterium tuberculosis.
  
  
  METHODS
  The genes rrs and tlyA and the promoter region of eis of 152 M. tuberculosis clinical isolates (including 55 capreomycin resistant) and 44 in vitro selected capreomycin-, amikacin- and kanamycin-resistant mutants were sequenced. In addition, MICs of capreomycin, amikacin and kanamycin on Middlebrook 7H10 were determined.
  
  
  RESULTS
  The results clearly show major differences in genotypes and cross-resistance patterns to amikacin and kanamycin between the capreomycin-resistant clinical isolates and in vitro selected mutants. tlyA mutations were found almost exclusively among the in vitro selected capreomycin-resistant mutants, while only four were found among the clinical isolates, of which two were capreomycin susceptible. In contrast, 53 of the 55 capreomycin-resistant clinical isolates had a mutation at position 1401 in rrs and were resistant to capreomycin, amikacin and kanamycin. Low-level resistance to kanamycin was correlated to mutations in the promoter region of eis.
  
  
  CONCLUSIONS
  Our findings are consistent with the belief that a mutation at position 1401 in rrs leads to resistance to capreomycin, amikacin and kanamycin. The data also show that tlyA is not a sensitive genetic marker for capreomycin resistance in clinical isolates of M. tuberculosis, as mutations in this gene are infrequent and not all mutations in tlyA lead to capreomycin resistance.
authors.affiliation: Swedish Institute for Infectious Disease Control (SMI), Solna, Sweden. anna.engstrom@smi.se
authors.forename: Anna
authors.initials: A
authors.lastname: Engström
authors.forename: Nasrin
authors.initials: N
authors.lastname: Perskvist
authors.forename: Jim
authors.initials: J
authors.lastname: Werngren
authors.forename: Sven E
authors.initials: SE
authors.lastname: Hoffner
authors.forename: Pontus
authors.initials: P
authors.lastname: Juréen
mesh_terms: D000123:Acetyltransferases; D000583:Amikacin / Q000494:pharmacology; D000942:Antigens, Bacterial / Q000235:genetics; D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D002207:Capreomycin / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial; D005819:Genetic Markers; D006801:Humans; D007612:Kanamycin / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics*; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA
chemical_list: D000942:Antigens, Bacterial; D000995:Antitubercular Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D005819:Genetic Markers; D012336:RNA, Ribosomal, 16S; C112817:TlyA protein, Mycobacterium tuberculosis; D002207:Capreomycin; D007612:Kanamycin; D000583:Amikacin; D000123:Acetyltransferases; C430563:Eis protein, Mycobacterium tuberculosis