Background

Amikacin is a first-line drug that must be evaluated when performing an antimycobacterial susceptibility test (AST) for Mycobacterium avium complex (MAC). However, the presence of sporadic trailing growth in MAC makes determining the precise point for reading its minimal inhibitory concentration (MIC) challenging.

Methods

Susceptibility was re-tested for 134 MAC clinical isolates using the Sensititre SLOMYCOI panel, the rrs gene was sequenced, and amikacin exposure history was investigated. The MIC₅₀, MIC₉₀, and the epidemiological cut-off value (ECOFF) were calculated using the EUCAST method.

Results

After re-testing and ignoring trailing growth, of the 22 M. intracellulare isolates originally classified as resistant to amikacin according to the CLSI guideline, 10 strains were reclassified as intermediate and four as susceptible. Similarly, from the seven resistant M. avium strains, one was reclassified as intermediate and four as susceptible. No rrs gene mutations were detected in any isolates, including resistant strains. When ignoring trailing growth, the calculated MIC₅₀, MIC₉₀, and ECOFF values closely aligned with the EUCAST MIC distribution.

Conclusion

To maintain the current CLSI breakpoint, trailing growth should be ignored when reading the amikacin MIC of MAC. To read the MIC at complete bacterial inhibition, the CLSI breakpoint needs to be raised.

中文翻译：

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评估鸟分枝杆菌复合体生长过程中阿米卡星最低抑菌浓度

背景

阿米卡星是一线药物，在进行鸟分枝杆菌复合体 (MAC) 的抗分枝杆菌药敏试验 (AST) 时必须对其进行评估。然而，MAC 中零星拖尾生长的存在使得确定读取其最小抑菌浓度 (MIC) 的精确点具有挑战性。

方法

使用 Sensititre SLOMYCOI panel 重新测试了 134 个 MAC 临床分离株的敏感性，对rrs基因进行了测序，并调查了阿米卡星暴露史。使用EUCAST方法计算MIC ₅₀、MIC ₉₀和流行病学临界值(ECOFF)。

结果

经过重新测试并忽略拖尾生长后， 根据 CLSI 指南最初被分类为阿米卡星耐药的22 个胞内分枝杆菌分离株中，10 个菌株被重新分类为中间菌株，4 个菌株被重新分类为敏感菌株。同样，在七种抗性鸟分枝杆菌菌株中，一种被重新分类为中间菌株，四种被重新分类为敏感菌株。在任何分离株（包括耐药株）中均未检测到rrs基因突变。当忽略尾随生长时，计算出的 MIC ₅₀、MIC ₉₀和 ECOFF 值与 EUCAST MIC 分布紧密一致。

结论

为了维持当前的 CLSI 断点，在读取 MAC 的阿米卡星 MIC 时应忽略尾随增长。要读取细菌完全抑制时的 MIC，需要提高 CLSI 断点。