P032

1:AP-HP Sorbonne University; 2:Centre National de Référence des Mycobactéries et de la Résistance des Mycobactéries aux Antituberculeux; 3:AP-HP GHU Nord; 4:UPMC - Paris 6

Drug Susceptibility Testing (DST) is crucial for optimizing therapeutic choices in non-tuberculous mycobacterial (NTM) infection. While broth microdilution is the reference method, commercially available SLOMYCO Sensititreᵀᴹ plates have two main drawbacks: inappropriate concentration ranges for some antibiotics and the absence of clinically relevant agents, such as bedaquiline (BDQ) and clofazimine (CFZ). To overcome these limitations, we designed customized Sensititreᵀᴹ plates (FRATMYC1, FRATMYC2) and aimed to (i) test antibiotics missing from standard panels and (ii) evaluate the concordance of first-line antibiotics’ MICs measured using SLOMYCO and FRATMYC plates for Mycobacterium avium complex (MAC) clinical isolates.

We tested 73 MAC strains (31 M. avium, 23 M. chimaera and 19 M. intracellulare), collected between 2018 and 2024, including the reference strain M. avium MAC101 (ATCC700898). Species identification was performed using routine procedures (i.e. line probe assays,GenoType NTM-DR, Bruker, Germany). MICs were determined using all three Sensititreᵀᴹ plates according to CLSI guidelines. Agreement between methods was defined as MICs within ±1 log2 dilution.

BDQ and CFZ exhibited the lowest MIC90 (0.06 mg/L and 0.12 mg/L, respectively), regardless of susceptibility to clarithromycin (CLR) and amikacin, based on 11 CLR-resistant and 6 amikacin-resistant isolates, including 3 resistant to both. Agreement rates between SLOMYCO and FRATMYC were 72.2% for CLR and 77.8% for amikacin, with categorical agreement of 98.6% and 90.3%, respectively.

FRATMYC plates provided comparable results to SLOMYCO while expanding DST to clinically relevant agents. BDQ and CFZ demonstrated strong in vitro activity and should be considered in routine DST for slow-growing NTM.