title: Rapid Detection of Isoniazid Resistance in Mycobacterium tuberculosis by a Single Multiplex Allele-specific Polymerase Chain Reaction Assay.
abstract: OBJECTIVE
  Global surveillance has shown that drug resistant (DR) tuberculosis (TB) is widespread. Prompt detection of Mycobacterium tuberculosis drug resistance is essential for effective control of TB. The most frequent mutations associated with Isoniazid (INH) resistance in Mycobacterium are substitutions at codons 315 in the katG gene and the mabA-inhA promoter region (-15). This survey evaluated INH resistant-associated mutations in order to determine rapid detection of TB resistance.
  
  
  METHODS
  Through a descriptive cross- sectional study total of 96 sputum specimens were digested, examined microscopically for acid-fast bacilli and inoculated into Löwenstein-Jensen slants. Thereafter, the susceptibility and identification tests were performed on culture positive specimens. Subsequently, the strains were subjected to multiplex allele-specific polymerase chain reaction (MAS-PCR) targeting in the codons 315 in the katG gene and the mabA-inhA promoter region. Distinct PCR banding patterns were observed for different mutation profiles.
  
  
  RESULTS
  Drug susceptibility testing revealed that out of 96 available isolates, 30 (31.3%) were susceptible, 36 (37.5%) had multi-drug resistance (MDR-TB) and 30 (31.3%) showed mono- drug resistance. In comparison with the culture-based phenotypic drug susceptibility test, the sensitivity and specificity of MAS-PCR assay for drug resistance-related genetic mutations were 76.7% and 71.4%, respectively. The correlation between MAS-PCR and culture-based phenotypic drug susceptibility testing findings was 99.4%.
  
  
  CONCLUSIONS
  The profile of the isolates suggests a significant number of different DR strains with a high frequency of mutations at codon 315 of the katG gene. MAS-PCR provides a rapid, simple and cost-effective method for detecting MDR-TB.
authors.affiliation: 1. Mycobacteriology Research Centre, Shahid Beheshti Medical University, Tehran, Iran.
authors.forename: Kimia
authors.initials: K
authors.lastname: Taghavi
authors.forename: Parissa
authors.initials: P
authors.lastname: Farnia
authors.forename: Mohammad
authors.initials: M
authors.lastname: Varahram
authors.forename: Fatemeh Maryam
authors.initials: FM
authors.lastname: Sheikhoslami
authors.forename: Mojtaba
authors.initials: M
authors.lastname: Ahmadi
authors.forename: Mehdi
authors.initials: M
authors.lastname: Kazempoor
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Masjedi
authors.forename: Ali Akbar
authors.initials: AA
authors.lastname: Velayati
keywords: Multidrug Resistant; PCR; Tuberculosis