Utility of mycobacterial dna extract from used Xpert mtb/rif cartridges for second line genotypic Drug susceptibility testing at eastern and western Oromia, Ethiopia

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.