Table 1.Assessment of cross-reactivity in RIF resistance detection by Xpert and Xpert Ultra with NTM species at high bacterial load

Ann Clin Microbiol 2025;28(4):21. Impact of nontuberculous mycobacteria on the performance of Xpert MTB/RIF and Xpert MTB/RIF Ultra for the detection of tuberculosis and rifampin resistance: a diagnostic accuracy study

Table 1.Assessment of cross-reactivity in RIF resistance detection by Xpert and Xpert Ultra with NTM species at high bacterial load

NTM strain (1.0 × 10⁶ CFU/mL equivalent)	MTB (5.0 × 10³ CFU/mL equivalent)	Xpert result				Xpert Ultra result
		1^st		2^nd		1^st		2^nd
		MTB	RIF resistance	MTB	RIF resistance	MTB	RIF resistance (Mutant Tm,rpoB3/rpoB4-A)	MTB	RIF resistance (Mutant Tm,rpoB3/rpoB4-A)
M. avium (KMRC 0136-41011)	RS	D, Low	ND	D, Low	ND	D, Very low	ND	D, Low	ND
M. avium (KMRC 0136-41011)	RR	D, Low	D	D, Low	D	D, Low	D (73.7/73.8)	D, Trace	Indeterminate
M. intracellulare (ATCC 13950)	RS	D, Low	ND	D, Low	ND	D, Low	ND	D, Low	ND
M. intracellulare (ATCC 13950)	RR	D, Low	D	D, Low	D	D, Low	D (73.7/73.8)	D, Low	D (73.7/73.8)
M. kansasii (ATCC 12478)	RS	D, Low	ND	D, Low	ND	D, Low	ND	D, Low	ND
M. kansasii (ATCC 12478)	RR	D, Low	D	D, Low	D	D, Low	D (73.7/73.7)	D, Low	D (73.4/73.8)
M. abscessus subsp. abscessus (ATCC 19977)	RS	D, Low	ND	D, Low	ND	D, Low	ND	D, Low	ND
M. abscessus subsp. abscessus (ATCC 19977)	RR	D, Low	D	D, Low	D	D, Low	D (73.4/73.7)	D, Low	D (73.2/73.6)
M. abscessus subsp. massiliense (CCUG 48898)	RS	D, Low	ND	D, Low	ND	D, Low	ND	D, Low	ND
M. abscessus subsp. massiliense (CCUG 48898)	RR	D, Low	D	D, Low	D	D, Low	D (73.5/73.8)	D, Low	D (72.8/73.3)
M. gordonae (ATCC 14470)	RS	D, Low	ND	D, Medium	ND	D, Low	ND	D, Low	ND
M. gordonae (ATCC 14470)	RR	D, Low	D	D, Low	D	D, Low	D (73.6/73.7)	D, Low	D (73.5/73.8)
M. chelonae (ATCC 35752)	RS	D, Low	ND	D, Low	ND	D, Low	ND	D, Low	ND
M. chelonae (ATCC 35752)	RR	D, Low	D	D, Low	D	D, Low	D (73.8/73.8)	D, Low	D (73.5/73.9)
M. fortuitum (KMRC 0136-60004)	RS	D, Low	ND	D, Low	ND	D, Low	ND	D, Very low	ND
M. fortuitum (KMRC 0136-60004)	RR	D, Low	D	D, Low	D	D, Low	D (72.7/73.3)	D, Low	D (73.4/73.7)

Abbreviations: RIF, rifampin; NTM, nontuberculous mycobacteria; CFU, colony-forming unit; MTB, Mycobacterium tuberculosis; KMRC, Korea Mycobacterium Resource Center; ATCC, American Type Culture Collection; CCUG, Culture Collection University of Göteborg; D, detected; ND, not detected; RS, rifampin-susceptible reference strain (H37Rv, ATCC 27294); RR, rifampin-resistant clinical isolate with S450L mutation.