title: Application of hyperbranched rolling circle amplification for direct detection of mycobacterium tuberculosis in clinical sputum specimens.
abstract: BACKGROUND
  Global tuberculosis (TB) control is encumbered by the lack of a rapid and simple detection method for diagnosis, especially in low-resource areas. An isothermal amplification method, hyperbranched rolling circle amplification (HRCA), was optimized to detect Mycobacterium tuberculosis (Mtb) in clinical sputum specimens.
  
  
  METHODS
  A clinical validation study was performed to assess the diagnostic accuracy of HRCA. In order to analyze the detection limit of HRCA under optimal conditions, the method was initially used to detect purified H37Rv strain DNA and culture suspensions. Next, three strains of Mycobacterium tuberculosis complex (MTC) and eight strains of non-tuberculosis mycobacterium (NTM) were analyzed in order to evaluate specificity. Sputum specimens from 136 patients with diagnosed pulmonary TB, 38 lung cancer patients, and 34 healthy donors were tested by HRCA to validate the clinical application of HRCA for the rapid detection of Mtb.
  
  
  RESULTS
  The detection limit of HRCA for purified H37Rv DNA and culture suspensions was 740 aM and 200cfu/ml, respectively. The results of all MTC strains were positive in contrast to the NTM specimens which were all negative. The detection sensitivity for the 136 sputum specimens from TB patients was 77.2% (105/136), which was slightly lower than that of quantitative real-time PCR(79.4%, 108/136) and culture (80.9%,110/136). The sensitivity of all three methods was statistically higher than smear microscopy (44.9%, 61/136). The overall specificity of HRCA was 98.6% (71/72) which was similar to that of quantitative real-time PCR (qRT-PCR) and smear/culture methods (100%, 72/72).
  
  
  CONCLUSIONS
  Use of the HRCA assay for detection of Mtb within clinical sputum specimens was demonstrated to be highly sensitive and specific. Moreover, the performance of HRCA is simple and cost-effective compared with qRT-PCR and is less time consuming than culture. Therefore, HRCA is a promising TB diagnostic tool that can be used routinely in low-resource clinical settings.
authors.affiliation: Laboratory of Molecular Biology for Tuberculosis, Beijing Tuberculosis and Thoracic Tumor Research Institute, Beijing Chest Hospital, Capital Medical University, Beijing, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Yan-Ling
authors.initials: YL
authors.lastname: Guo
authors.forename: Guang-Lu
authors.initials: GL
authors.lastname: Jiang
authors.forename: Shi-Jie
authors.initials: SJ
authors.lastname: Zhou
authors.forename: Qi
authors.initials: Q
authors.lastname: Sun
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.forename: Xiu-Jun
authors.initials: XJ
authors.lastname: Chang
authors.forename: Ai-Ying
authors.initials: AY
authors.lastname: Xing
authors.forename: Feng-Jiao
authors.initials: FJ
authors.lastname: Du
authors.forename: Hong-Yan
authors.initials: HY
authors.lastname: Jia
authors.forename: Zong-De
authors.initials: ZD
authors.lastname: Zhang
mesh_terms: D015331:Cohort Studies; D006761:Hospitals; D006801:Humans; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification* / Q000502:physiology; D021141:Nucleic Acid Amplification Techniques / Q000379:methods*; D012680:Sensitivity and Specificity; D013045:Species Specificity; D013183:Sputum / Q000382:microbiology*; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis / Q000382:microbiology