Demonstration of a fast and easy sample-to-answer protocol for tuberculosis screening in point-of-care settings: A proof of concept study

PLoS One. 2020 Dec 14;15(12):e0242408. doi: 10.1371/journal.pone.0242408. eCollection 2020.

Abstract

We sought to develop a smooth and low cost sample preparation and DNA extraction protocol, streamlined with a ready-to-use qPCR in a portable instrument to overcome some of the existing hurdles. Several solutions were evaluated as to their ability to liquefy a mucin-based matrix. Each liquefied matrix, supplemented with either Mycobacterium tuberculosis (MTB) H37Rv strain DNA or intact cells, was aliquoted onto a filter paper embedded with solubilizing agents, and was subsequently dried up. Most of the nucleic acids, including genomic DNA from the bacilli and the host, binds to the filter paper. Next, several protocols were evaluated to elute the DNA from the paper, using qPCR to detect the insertion sequence IS6110, a M. tuberculosis complex genomic marker. The limit of detection (LOD) of the best protocol was then evaluated using parallel seeding and colony counting. The protocol was also evaluated using seventeen sputum samples, previously characterized by the GeneXpert or culture. Two instruments (the ABI7500 Standard and the Q3-Plus system) and two reagents storage formats (frozen or ready-to-use) were evaluated. Solutions containing guanidine isothiocyanate exerted the best liquefying effect on the mucin-based matrix extracted from one 6-mm punches, followed by a brief incubation at 95°C. The resulting DNA contained impurities, but a simple 1:10 dilution elicited the detection of MTB and human genomic targets. The described protocol presented an apparent LOD of 02 CFU/mL of MTB. Challenging the protocol with previously characterized samples showed substantial agreement with GeneXpert MTB/RIF results (sensitivity of 90%, agreement of 88.9%, kappa coefficient of 0.77), and moderate agreement with culture results (sensitivity of 100%, agreement of 78.9%, kappa coefficient of 0.58). This work presents a sensitive proof-of-concept protocol for sputum liquefaction and decontamination followed by a simple DNA extraction procedure, in which the extraction steps are streamlined with a ready-to-use qPCR in a portable instrument that can be employed in low infrastructure settings.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Brazil
  • DNA, Bacterial / isolation & purification
  • Humans
  • Limit of Detection
  • Mass Screening / economics
  • Mass Screening / instrumentation
  • Mass Screening / methods*
  • Mycobacterium tuberculosis / genetics
  • Mycobacterium tuberculosis / isolation & purification*
  • Point-of-Care Systems*
  • Proof of Concept Study
  • Real-Time Polymerase Chain Reaction / economics
  • Real-Time Polymerase Chain Reaction / instrumentation
  • Real-Time Polymerase Chain Reaction / methods
  • Specimen Handling / economics
  • Specimen Handling / methods*
  • Sputum / microbiology
  • Tuberculosis, Pulmonary / diagnosis*
  • Tuberculosis, Pulmonary / microbiology

Substances

  • DNA, Bacterial

Grants and funding

Several authors received grants or fellowships from the Brazilian funding agencies CNPq and CAPES. This work was funded by a grant from the Banco Nacional de Desenvolvimento Econômico e Social (BNDES), contract no. 15.2.0473.1 (Operation #4.816.864), and by a grant from the Fundação de Amparo à Pesquisa do Rio Grande do Sul (FAPERGS grant #17/2551-0001542-8). There was no additional external funding received for this study. IBMP, BNDES, FAPERGS, CAPES or CNPq had no participation in the present study’s design, data collection, analysis or interpretation, or writing of the report and decision to submit for publication.