Association Between 16S rRNA Gene Mutations and Susceptibility to Amikacin in Mycobacterium avium Complex and Mycobacterium Abscessus Clinical Isolates
Abstract We evaluated the association between 16S rRNA gene (rrs) mutations and susceptibility in amikacin-resistant nontuberculous mycobacterial (NTM) clinical isolates in NTM- pulmonary disease (PD) patients. Susceptibility was retested for 134 amikacin-resistant isolates (minimum inhibitory concentration [MIC] ≥64 µg/ml) from 86 patients. Amikacin resistance was reconfirmed in 102 NTM isolates from 62 patients with either Mycobacterium avium complex-PD (MAC-PD) (n=54) or M. abscessus-PD (n=8). MIC and rrs mutations were evaluated for 318 single colonies from these isolates. For the 54 MAC-PD patients, rrs mutations were present in all isolates (obtained from 31 patients) with an amikacin MIC ≥128 µg/ml, but only in a few isolates (from three of 23 patients) with an MIC=64 µg/ml. For the eight M. abscessus-PD patients, all amikacin-resistant isolates (MIC ≥64 µg/ml) had rrs mutations. Of amikacin resistance isolates, A1408G mutation (n=29) was most common. Two novel mutations, C1496T and T1498A, were also identified. The culture conversion rate did not differ by amikacin MIC (20% for MIC=64µg/ml vs. 7% for MIC ≥128 µg/ml, p=0.468). In conclusion, all amikacin-resistant M. abscessus isolates had rrs mutations, but in MAC isolates showing relatively low resistance (MIC=64µg/ml), rrs mutations were infrequently identified.