title: Genome and MIC stability in Mycobacterium tuberculosis and indications for continuation of use of isoniazid in multidrug-resistant tuberculosis.
abstract: Mycobacterium tuberculosis strains resistant to two or more of the first line antituberculosis drugs (MDR) are a serious threat to successful tuberculosis control programmes. For this retrospective study, 85 follow-up drug resistant isolates from 23 patients residing in a community with a high incidence of tuberculosis were collected and the level of in-vitro resistance to antibiotics determined quantitatively. PCR-SSCP and sequencing techniques were used to screen for gene mutations associated with resistance in 31 follow-up samples from a smaller group of eight patients. DNA fingerprint analysis was done on sequential isolates to confirm identity. Although treatment had a profound effect on changes in drug resistance patterns, the MIC for a particular agent remained constant in follow-up isolates. DNA fingerprinting and mutational analysis (14 different loci) showed that the genome of MDR strains of M. tuberculosis is relatively stable during the course of therapy. The rpoB gene was the most frequently mutated structural gene involved in drug resistance and a novel C to T mutation upstream of open reading frame (ORF)1 of the inhA operon was detected. No evidence was found of the presence of strain W (New York) in this group of MDR strains. The results stress the importance of confirming individuality of strains for the accurate calculation of frequencies of particular mutations associated with drug resistance, particularly in a high incidence area. Approximately one-half (47.8%) of the patients had isolates resistant to concentrations just above the critical concentration for isoniazid (MICs of 0.2-5 mg/L). Therefore, these patients and their contacts who develop primary drug-resistant tuberculosis may respond to higher dosages of treatment which could have a considerable impact on the cost and the ease of management of resistant tuberculosis.
authors.affiliation: Department of Medical Biochemistry, Tygerberg Hospital, South Africa.
authors.forename: T C
authors.initials: TC
authors.lastname: Victor
authors.forename: R
authors.initials: R
authors.lastname: Warren
authors.forename: J L
authors.initials: JL
authors.lastname: Butt
authors.forename: A M
authors.initials: AM
authors.lastname: Jordaan
authors.forename: J V
authors.initials: JV
authors.lastname: Felix
authors.forename: A
authors.initials: A
authors.lastname: Venter
authors.forename: F A
authors.initials: FA
authors.lastname: Sirgel
authors.forename: H S
authors.initials: HS
authors.lastname: Schaaf
authors.forename: P R
authors.initials: PR
authors.lastname: Donald
authors.forename: M
authors.initials: M
authors.lastname: Richardson
authors.forename: M H
authors.initials: MH
authors.lastname: Cynamon
authors.forename: P D
authors.initials: PD
authors.lastname: Van Helden
mesh_terms: D000995:Antitubercular Agents / Q000627:therapeutic use*; D002374:Catalase / Q000032:analysis; D016172:DNA Fingerprinting; D004352:Drug Resistance, Microbial / Q000235:genetics; D018432:Drug Resistance, Multiple / Q000235:genetics*; D005500:Follow-Up Studies; D014644:Genetic Variation; D006801:Humans; D007538:Isoniazid / Q000627:therapeutic use*; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000235:genetics*; D016133:Polymerase Chain Reaction; D018807:Polymorphism, Single-Stranded Conformational; D012189:Retrospective Studies; D017422:Sequence Analysis, DNA; D013019:South Africa / Q000453:epidemiology; D014397:Tuberculosis, Pulmonary / Q000188:drug therapy* / Q000453:epidemiology / Q000382:microbiology
chemical_list: D000995:Antitubercular Agents; D002374:Catalase; D007538:Isoniazid