标题：Extract from used Xpert MTB/RIF Ultra cartridges is useful for accurate second-line drug-resistant tuberculosis diagnosis with minimal rpoB-amplicon cross-contamination risk
摘要：Xpert MTB/RIF Ultra (Ultra) detects Mycobacterium tuberculosis and rifampicin resistance. Follow-on drug susceptibility testing (DST) requires additional sputum. Extract from the diamond-shaped chamber of the cartridge (dCE) of Ultra’s predecessor, Xpert MTB/RIF (Xpert), is useful for MTBDR sl -based DST but this is unexplored with Ultra. Furthermore, whether CE from non-diamond compartments is useful, the performance of FluoroType MTBDR (FT) on CE, and rpoB cross-contamination risk associated with the extraction procedure are unknown. We tested MTBDR sl , MTBDR plus , and FT on CEs from chambers from cartridges (Ultra, Xpert) tested on bacilli dilution series. MTBDR sl on Ultra dCE on TB-positive sputa (n = 40) was also evaluated and, separately, rpoB amplicon cross-contamination risk . MTBDR sl on Ultra dCE from dilutions ≥10 3 CFU/ml (C Tmin “low semi-quantitation”) detected fluoroquinolone (FQ) and second-line injectable (SLID) susceptibility and resistance correctly (some SLIDs-indeterminate). At the same threshold (at which ~85% of Ultra-positives in our setting would be eligible), 35/35 (100%) FQ and 34/35 (97%) SLID results from Ultra dCE were concordant with sputa results. Tests on other chambers were unfeasible. No tubes open during 20 batched extractions had FT-detected rpoB cross-contamination. False-positive Ultra rpoB results was observed when dCE dilutions ≤10 −3 were re-tested. MTBDR sl on Ultra dCE is concordant with isolate results. rpoB amplicon cross-contamination is unlikely. These data mitigate additional specimen collection for second-line DST and cross-contamination concerns.
