title: Laboratory evaluation of a specimen transport medium for downstream molecular processing of sputum samples to detect Mycobacterium tuberculosis.
abstract: BACKGROUND
  Modern molecular-based approaches for the detection of Mycobacterium tuberculosis in sputum samples promise quicker and more accurate detection of cases. However, processing sputum samples at central diagnostic facilities provides a diagnostic approach, but requires a safe and efficient system that is not affected by transport delays and ambient temperature to be feasible. We evaluated the technical properties of PrimeStore®-Molecular Transport Medium (PS-MTM) for its ability to inactivate mycobacteria, ensuring stability of DNA over time at ambient temperatures and to assess the compatibility of the transport medium with DNA extraction systems.
  
  
  METHODS
  Assessment of the transport medium for application of sputum samples processed for the detection of M. tuberculosis included the inactivation of M. tuberculosis in spiked sputum samples, compatibility of the medium with three commercial nucleic extraction systems and stability of DNA in the medium at ambient temperature over 28 days. We further performed a clinical laboratory evaluation on 256 sputum specimens sent for tuberculosis investigation.
  
  
  RESULTS
  Complete inactivation of M. tuberculosis occurred within 30 min of exposure at a ratio of 1:3 for sputum to PS-MTM. Sputum specimen in PS-MTM showed very good compatibility with automated bead-based extraction systems, producing high DNA output (estimated lower limits of detection: ~170 CFU/ml). Furthermore, PS-MTM samples remained stable over 28 days at ambient temperature displaying no significant change over time in Ct-values (<5% on a mean starting value of 22.47). Of the 256 clinical sputum specimens, 10.2% were culture positive and 11.0% were positive by real-time PCR of PS-MTM samples.
  
  
  CONCLUSIONS
  Collecting and transporting sputum from TB suspects in PS-MTM offer safe transport at ambient temperature, DNA stability for extended periods without cooling and specimens directly suitable for molecular testing. This novel approach may support introduction and further scale-up of molecular diagnostics for TB in resource-limited settings.
authors.affiliation: Faculty of Health Sciences, Department of Medical Microbiology, University of Pretoria, Pretoria, South Africa; Centre for Tuberculosis, National TB Reference Laboratory, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa. Electronic address: shaheedvo@nicd.ac.za.
authors.forename: Shaheed V
authors.initials: SV
authors.lastname: Omar
authors.affiliation: Faculty of Health Sciences, Department of Medical Microbiology, University of Pretoria, Pretoria, South Africa; Anova Health Institute, Johannesburg, South Africa.
authors.forename: Remco P H
authors.initials: RP
authors.lastname: Peters
authors.affiliation: Faculty of Health Sciences, Department of Medical Microbiology, University of Pretoria, Pretoria, South Africa; Centre for Tuberculosis, National TB Reference Laboratory, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Nazir A
authors.initials: NA
authors.lastname: Ismail
authors.affiliation: Centre for Tuberculosis, National TB Reference Laboratory, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Andries W
authors.initials: AW
authors.lastname: Dreyer
authors.affiliation: Centre for Tuberculosis, National TB Reference Laboratory, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Halima M
authors.initials: HM
authors.lastname: Said
authors.affiliation: Centre for Tuberculosis, National TB Reference Laboratory, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Thabisile
authors.initials: T
authors.lastname: Gwala
authors.affiliation: Centre for Tuberculosis, National TB Reference Laboratory, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Nabila
authors.initials: N
authors.lastname: Ismail
authors.affiliation: Faculty of Health Sciences, Department of Medical Microbiology, University of Pretoria, Pretoria, South Africa.
authors.forename: P Bernard
authors.initials: PB
authors.lastname: Fourie
mesh_terms: D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D058889:Molecular Typing / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D013048:Specimen Handling / Q000379:methods*; D013183:Sputum / Q000382:microbiology*; D014376:Tuberculosis / Q000175:diagnosis / Q000382:microbiology
chemical_list: D003470:Culture Media
keywords: DNA stability; Molecular detection; Mycobacterium tuberculosis; Specimen transport medium