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Volume 19, Number 3—March 2013
Letter

Mycobacterium tuberculosis Beijing Type Mutation Frequency

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To the Editor: A striking finding in the study by de Steenwinkel et al. (1) is the high frequency of mutation to rifampin resistance by 2 Mycobacterium tuberculosis Beijing strains, which might play a role in the association between the Beijing strains and multidrug-resistant tuberculosis. Earlier reported frequency of mutation to rifampin resistance by M. tuberculosis has been 10−8 CFU (2,3), including the Beijing genotype (3,4). Of note, the Beijing 2002–1585 strain, for which frequency of mutation to rifampin resistance is 10−3 CFU (1 mutant/1,000 CFU), showed a moderate frequency of 10−8 CFU in another study (4). We think that a mutation frequency increase of 100,000× is remarkably high. In contrast, rifampin-resistant mutants of the Beijing 1585 strain did not emerge in low-density cultures (5 × 105 CFU/mL) used for time-kill kinetics experiments, although frequency of mutation to rifampin resistance was determined to be 10−3 CFU.

Mutation frequency is determined by fluctuation assays. To exclude preexisting mutants, which would bias the mutation frequency by so-called jackpots, a series of low-inoculum cultures is typically used (5). However, for unknown reasons, de Steenwinkel et al. used only 1 high-density culture of 1010 CFU of each strain to determine mutation frequency. This strategy is not recommended because mutations can occur early or late, resulting in substantial mutation frequency fluctuation between test episodes. A strain with known mutation rates should preferably be included to rule out possible technical errors.

We propose the following explanations for the remarkable results: 1) the rifampin concentration for selecting mutants might have been too low, enabling growth of some colonies of drug-susceptible bacteria; 2) rifampin mutants arose early or preexisted in the cultivation of Beijing strains 1585 and 1607, producing jackpots; or 3) the 2 Beijing isolates might contain rifampin-resistant subpopulations (heteroresistance). The capacity of the Beijing strain to develop and, especially, transmit multidrug-resistant tuberculosis remains to be further analyzed.

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Jim WerngrenComments to Author 

Author affiliation: Author affiliation: Swedish Institute for Communicable Disease Control, Solna, Sweden

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References

  1. de Steenwinkel  JEM, ten Kate  MT, de Knegt  GJ, Kremer  K, Aarnoutse  RE, Boeree  MJ, Drug susceptibility of Mycobacterium tuberculosis Beijing genotype, association with MDR TB. Emerg Infect Dis. 2012;4:6603. DOIPubMed
  2. David  HL. Probability distribution of drug-resistant mutants in unselected populations of Mycobacterium tuberculosis. Appl Microbiol. 1970;20:8104.PubMed
  3. Werngren  J, Hoffner  SE. Drug-susceptible Mycobacterium tuberculosis Beijing genotype does not develop mutation-conferred resistance to rifampin at an elevated rate. J Clin Microbiol. 2003;41:15204. DOIPubMed
  4. Bergval  I, Kwok  B, Schuitema  K, Kremer  K, van Soolingen  D, Klatser  P, Pre-existing isoniazid resistance, but not the genotype of Mycobacterium tuberculosis drives rifampicin resistance codon preference in vitro. PLoS ONE. 2012;7:e29108. DOIPubMed
  5. Gillespie  SH. Evolution of drug resistance in Mycobacterium tuberculosis: clinical and molecular perspective. Antimicrob Agents Chemother. 2002;46:26774. DOIPubMed

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Cite This Article

DOI: 10.3201/eid1903.121001

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Table of Contents – Volume 19, Number 3—March 2013

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Please use the form below to submit correspondence to the authors or contact them at the following address:

Jim Werngren, Unit of Highly Pathogenic Microorganisms, Dept of Preparedness, Swedish Institute for Communicable Disease Control, Nobels väg 18 S-17182, Solna, Stockholm S 17182, Sweden

Address for correspondence: J.E.M. de Steenwinkel, Erasmus MC, Room L-327, PO Box 2040, 3000 CA, Rotterdam, the Netherlands; email: j.desteenwinkel@erasmusmc.nl

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Page created: January 17, 2013
Page updated: January 17, 2013
Page reviewed: January 17, 2013
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
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