Abstract:
Background: The emergence and spread of multidrug-resistant tuberculosis (MDR-TB) and
extensive drug resistance (XDR-TB) is a threat to tuberculosis (TB) treatment, as only a few of
these patients have access to drug susceptibility testing (DST). Xpert MTB/RIF is a test used for
TB and rifampicin-resistance detection. Second-line genotypic DST, which is recommended by
World Health Organization (WHO), requires additional specimen collection. This study aimed to
determine the utility of mycobacterial genomic DNA extract from used Xpert cartridges for
second-line DST, which may help patients to receive a diagnosis rapidly from a single specimen.
Objectives: To evaluate the Utility of Mycobacterial DNA extract from used Xpert MTB/RIF
cartridges for second-line genotypic DST at eastern and western Oromia, Ethiopia
Methods: A cross-sectional study was conducted on 62 samples collected from two TB referral
units in Ethiopia between June 2020 and May 2021. Collected sputum samples were allocated
into two and processed by Xpert MTB/RIF and culture. Fifty used Xpert rifampicin-resistant (RR)
cartridges were used for the mycobacterial genomic DNA extraction for second-line DST (SLDST)
by line probe assay. Descriptive statistics were performed using frequencies and
percentages to describe the characteristics of the study population. The yield of a method was
compared with DST performed on culture isolates.
Result: Of the 62 collected samples, Xpert detected M. tuberculosis (MTB) and RR-TB in 50
sputum samples. The sensitivity of MTBDRplus for rifampicin-resistant detection on cartridge
extract (CE) was 22% and the assay was not feasible on CE. MTBDRsl had 100 % actionable
results on CE for MTB detection. No resistance was found in any cartridge extract that was
subjected to analysis. From CE and isolates, assay had a concordance of 100% and 90% for FLQ
and SLID resistance detection respectively. All cartridge extract corresponding to CT value
(CT≤22) had interpretable results.
Conclusion: MTBDRsl on CE has a high level of agreement with that from isolates. Our data
showed that at the CT ≤ 22, CE from Xpert can be used for genotypic second-line DST. This
demonstrates further testing of the second-line anti-TB drug resistance can be done directly on
the used Xpert cartridge and minimize the time and resource needed for culture and mitigate
additional sample collection. Further study with a large sample size is recommended.
